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data-v-4bfbebcc><!--[--><p class="text" data-v-4bfbebcc>深入理解浏览器缓存机制</p><!--]--></a><!----></div><!----></div><div class="VPSidebarItem level-1 is-link" data-v-4bfbebcc data-v-4bfbebcc><div class="item" data-v-4bfbebcc><div class="indicator" data-v-4bfbebcc></div><a class="VPLink link link" href="/article/%E6%B7%B1%E5%85%A5%E7%90%86%E8%A7%A3%E6%B5%8F%E8%A7%88%E5%99%A8%E8%BF%90%E8%A1%8C%E5%8E%9F%E7%90%86.html" data-v-4bfbebcc><!--[--><p class="text" data-v-4bfbebcc>深入理解浏览器运行原理</p><!--]--></a><!----></div><!----></div><!--]--></div></section></div><!--]--><!--[--><!--]--></nav></aside><div class="VPContent has-sidebar" id="VPContent" data-v-aa0dbd16 data-v-e7387019><div class="VPDoc has-sidebar has-aside" data-v-e7387019 data-v-0ef3a6cc><!--[--><!--]--><div class="container" data-v-0ef3a6cc><div class="aside" data-v-0ef3a6cc><div class="aside-curtain" data-v-0ef3a6cc></div><div class="aside-container" data-v-0ef3a6cc><div class="aside-content" data-v-0ef3a6cc><div class="VPDocAside" data-v-0ef3a6cc data-v-dda43dd4><!--[--><!--]--><!--[--><!--]--><div class="VPDocAsideOutline" role="navigation" data-v-dda43dd4 data-v-64ee8e19><div class="content" data-v-64ee8e19><div class="outline-marker" data-v-64ee8e19></div><div class="outline-title" role="heading" aria-level="2" data-v-64ee8e19>On this page</div><nav aria-labelledby="doc-outline-aria-label" data-v-64ee8e19><span class="visually-hidden" id="doc-outline-aria-label" data-v-64ee8e19> Table of Contents for current page </span><ul class="VPDocOutlineItem root" data-v-64ee8e19 data-v-1f630f88><!--[--><!--]--></ul></nav></div></div><!--[--><!--]--><div class="spacer" data-v-dda43dd4></div><!--[--><!--]--><!----><!--[--><!--]--><!--[--><!--]--></div></div></div></div><div class="content" data-v-0ef3a6cc><div class="content-container" data-v-0ef3a6cc><!--[--><!--]--><main class="main" data-v-0ef3a6cc><div style="position:relative;" class="vp-doc _note_Rust" data-v-0ef3a6cc><div><h1 id="rust" tabindex="-1">Rust <a class="header-anchor" href="#rust" aria-label="Permalink to &quot;Rust&quot;">​</a></h1><h2 id="rust-环境搭建" tabindex="-1">Rust 环境搭建 <a class="header-anchor" href="#rust-环境搭建" aria-label="Permalink to &quot;Rust 环境搭建&quot;">​</a></h2><p><code>rustup</code> 是一个用于管理 Rust 版本和相关工具的命令行工具。</p><p>Unix 系统:</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">$</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> curl</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> --proto</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &#39;=https&#39;</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> --tlsv1.2</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> https://sh.rustup.rs</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> -sSf</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> sh</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>Windows 系统:</p><p>下载并安装 <a href="https://static.rust-lang.org/rustup/dist/i686-pc-windows-gnu/rustup-init.exe" target="_blank" rel="noreferrer">rustup-init.exe</a>.</p><p>安装完毕后，在命令行执行：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">rustc</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> --version</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>可以看到输出的版本号信息，则 rust 已安装完毕。</p><h2 id="hello-rust" tabindex="-1">Hello, Rust! <a class="header-anchor" href="#hello-rust" aria-label="Permalink to &quot;Hello, Rust!&quot;">​</a></h2><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">mkdir</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> hello_rust</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>创建并编辑第一个 Rust 程序：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// main.rs</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello, Rust!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>执行 <code>rustc ./hello_rust/main.rs</code></p><p>可以看到在代码同目录下输出了二进制文件 <code>main</code>，在命令行中执行：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">./main</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>可以看到输出：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Hello, Rust</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">!</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>下面我们分析一下这个程序：</p><p>在 Rust 中，函数名为 <code>main</code> 的函数是一个特殊的函数，它总是会被最先执行：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>在函数体中的代码：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello, Rust!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p><code>println!</code> 是一个 Rust 宏（macro），它与函数调用的区别是它以 <code>!</code> 结尾。</p><p><code>&quot;Hello, Rust!&quot;</code> 是一个字符串，传递给了 <code>println!</code> 宏。</p><p><strong>Rust 程序的编译和运行是独立进行的，这意味着你可以将编译产物直接发送给别人，别人不需要安装 Rust 也可以运行</strong></p><p>这与 Ruby Python JavaScript 这类动态语言不同，Rust 是一门<strong>预编译静态语言</strong>（ahead-of-time compiled）</p><p>简单项目可以使用 rustc，但随着项目复杂度增长，我们可以使用 cargo 来管理项目中的三方依赖、管理真实世界中 Rust 程序开发的方方面面。</p><h2 id="cargo" tabindex="-1">Cargo <a class="header-anchor" href="#cargo" aria-label="Permalink to &quot;Cargo&quot;">​</a></h2><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 初始化一个 Cargo 项目</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> new</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> hello_cargo</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>执行 <code>cargo new</code> 后会自动帮你初始化一个 Git 仓库，如果你是在一个现存的 Git 仓库中执行的初始化，那么就不会执行此操作。</p><p>除了帮你创建了一个 HelloWorld 代码，<code>cargo</code> 还创建了一个 <code>cargo.toml</code> 文件：</p><div class="language-toml vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">toml</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">[</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">package</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">]</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">name = </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;hello_cargo&quot;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">version = </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;0.1.0&quot;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">edition = </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;2021&quot;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">[</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">dependencies</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">]</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p><code>[package]</code>、<code>[dependencies]</code> 分别代表是一个片段：</p><ul><li>其中 <code>[package]</code> 下的字段 <code>name</code>、<code>version</code> 和 <code>edition</code> 表示项目的名称、项目的版本和使用的 Rust 版本。</li><li><code>[dependenciese]</code> 中记录着项目的第三方依赖，这些依赖被称为 <em>crates</em></li></ul><p>Cargo 期望所有的源代码都存放在 <code>src/</code> 目录下，项目根目录中保存如 README、LICENSE 这类的文件。</p><h3 id="在-cargo-中构建和运行项目" tabindex="-1">在 Cargo 中构建和运行项目 <a class="header-anchor" href="#在-cargo-中构建和运行项目" aria-label="Permalink to &quot;在 Cargo 中构建和运行项目&quot;">​</a></h3><p>执行 <code>cargo build</code> 可以构建项目：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> build</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>构建产物将输出在 <code>target/debug/</code> 目录下，这是因为 <code>cargo build</code> 是调试构建（debug build）</p><p>执行：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> run</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>即可运行刚刚 build 输出的产物。如果你在 <code>cargo run</code> 之前未构建或修改了代码，<code>cargo</code> 会自动帮你完成 re-build 并执行代码。</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> check</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>这个命令可以帮你完成代码的静态检查且不输出任何文件，由于它不需要准备输出构建产物，所以它比 <code>cargo build</code> 要快得多。</p><h3 id="发布构建" tabindex="-1">发布构建 <a class="header-anchor" href="#发布构建" aria-label="Permalink to &quot;发布构建&quot;">​</a></h3><p>与调试构建不同，可以执行：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> build</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> --release</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>来构建一个用于生产环境的产物，这会在 <code>target/release/</code> 下输出产物而不是 <code>target/debug/</code> 下。</p><p>发布构建的产物往往有针对生产的更多优化，同时构建需要花费的时间也更长，这也是为什么要有调试构建与发布构建的区分：调试构建用于开发时更快的看到最终效果，需要经常快速地执行构建，而发布构建则是为了最终用户使用时构建的。</p><h2 id="gussing-game" tabindex="-1">Gussing Game <a class="header-anchor" href="#gussing-game" aria-label="Permalink to &quot;Gussing Game&quot;">​</a></h2><p>写一个猜数游戏：</p><p>使用 <code>use</code> 标识符来从标准库中引入 <code>io</code> 库，之后就可以在当前作用域中通过 <code>io:stdin()</code> 读取到用户输入：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> std</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">io;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Guess the number!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Please input your guess.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">new</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> io</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">stdin</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">read_line</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">expect</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Failed to read line&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You guessed: {guess}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><p>执行 <code>cargo run</code> 后测试一下：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Guess</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> the</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> number!</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Please</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> input</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> your</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> guess.</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">6</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">You</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> guessed:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 6</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><h3 id="使用变量保存数据" tabindex="-1">使用变量保存数据 <a class="header-anchor" href="#使用变量保存数据" aria-label="Permalink to &quot;使用变量保存数据&quot;">​</a></h3><p>在 Rust 中，使用 <code>let</code> 与 <code>const</code> 声明的变量默认都是不可变的，通过给 <code>let</code> 声明的变量加上 <code>mut</code> 标记，来让 guess 这个变量可变（mutatiable）</p><p><code>::new</code> 中的 <code>::</code> 表明：<code>new</code> 是 <code>String</code> 类型的一个关联函数，在一些语言中它被称之为静态方法（static function）</p><p>总的来说，<code>let mut guess = String::new();</code> 这一行创建了一个可变变量，当前它绑定到一个新的 <code>String</code> 空实例上。</p><h3 id="读取用户输入" tabindex="-1">读取用户输入 <a class="header-anchor" href="#读取用户输入" aria-label="Permalink to &quot;读取用户输入&quot;">​</a></h3><p>如果在程序开头我们没有使用 <code>use</code> 来引入 <code>io</code> 库，在代码中我们也可以这样写：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">std</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">io</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">stdin</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>来动态地引入 <code>io</code> 库，通过 <code>read_line</code> 来从标准输入句柄获取用户输入。</p><p>将 <code>&amp;mut guess</code> 传递给 <code>read_line</code>，其中 <code>&amp;</code> 表明传递的是一个变量的引用，同时由于变量是不可变的，<code>&amp;mut</code> 表示这个引用可以修改。</p><h3 id="使用-result-类型处理潜在错误" tabindex="-1">使用 Result 类型处理潜在错误 <a class="header-anchor" href="#使用-result-类型处理潜在错误" aria-label="Permalink to &quot;使用 Result 类型处理潜在错误&quot;">​</a></h3><p>前文中我们说 <code>read_line</code> 会持续地将用户输入附加到传递给它的字符串中，它也会返回一个 <code>Result</code> 类型的值。</p><p><code>Result</code> 类型是一个枚举类型，包含两种成员类型：</p><ul><li><code>Ok</code>: 表示操作成功，内部包含成功时产生的值；</li><li><code>Err</code>: 表示操作失败，包含失败的前因后果。</li></ul><p>这些 <code>Result</code> 类型的作用是处理错误信息，<code>Result</code> 的实例具有 <code>expect</code> 方法，如果 <code>io:Result</code> 实例的值是 <code>Err</code>，<code>expect</code> 会导致程序崩溃，并显示错误信息。</p><p>如果 <code>read_line</code> 返回 <code>Err</code>，则可能是来源于底层操作系统错误的结果。如果 <code>Result</code> 实例的值是 <code>Ok</code>，<code>expect</code> 会获取 <code>Ok</code> 中的值并原样返回。</p><p>在此例子中，这个值是用户输入到标准输入中的字节数。</p><h3 id="使用-println-占位符打印值" tabindex="-1">使用 println! 占位符打印值 <a class="header-anchor" href="#使用-println-占位符打印值" aria-label="Permalink to &quot;使用 println! 占位符打印值&quot;">​</a></h3><p>下面这两种 <code>println!</code> 是等价的，他们都可以将变量打印到指定位置：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You guessed: {guess}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You guessed: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, guess);</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="生成一个随机数" tabindex="-1">生成一个随机数 <a class="header-anchor" href="#生成一个随机数" aria-label="Permalink to &quot;生成一个随机数&quot;">​</a></h3><p>在 Rust 标准库中不包含随机数功能，我们可以使用 rand crate：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> add</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> rand</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>安装后，我们到 Cargo.toml 中可以看到：</p><div class="language-toml vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">toml</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">[</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">dependencies</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">]</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">rand = </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;0.8.5&quot;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>这里的 <code>&quot;0.8.5&quot;</code> 实际上是 <code>&quot;^0.8.5&quot;</code> 的简写，它表示至少是 <code>0.8.5</code> 但小于 <code>0.9.0</code> 的版本。</p><p>具体可以参看<a href="https://semver.org/" target="_blank" rel="noreferrer">语义化版本（Semantic Versioning）</a></p><p>Cargo 通过 Cargo.lock 文件来保证每一次构建都是可以被重现的，任何人在任何时候重新构建代码都会产生相同的结果，Cargo 只会使用你指定的依赖版本。</p><blockquote><p>如果 rand 库下周发布了 <code>0.8.6</code> 版本，新版本中修复了一个 BUG 但存在破坏性变更，如果你没有显式地在 Cargo.toml 中升级 rand 库，那 Cargo 会按照上一次构建成功时生成的 Cargo.lock 记录的第三方库版本来构建。</p></blockquote><p>如果你确实要升级 crate，可以使用：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> update</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>来忽略 Cargo.lock 文件，并计算所有符合 Cargo.toml 声明的最新版本。</p><p>安装完了 rand crate，我们下面来生成一个随机数：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> std</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">io;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> rand</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Rng</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Guess the number!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> secret_number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> rand</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">thread_rng</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">gen_range</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">..=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">100</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;The secret number is: {secret_number}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Please input your guess.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">new</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> io</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">stdin</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">read_line</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">expect</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Failed to read line&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You guessed: {guess}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br></div></div><p><code>use rand:Rng;</code> 其中，<code>Rng</code> 是一个 trait，它定义了随机数生成器实现的方法的话，此 trait 必须在作用域中。</p><p>我们调用 <code>rand::thread_rng</code> 函数提供实际使用的<strong>随机数生成器</strong>：它位于当前执行线程的本地环境中，从操作系统获取 seed。</p><p>随后调用随机数生成器的 <code>gen_range</code> 方法，它由 <code>Rng</code> trait 定义，获取一个范围表达式（Range expression）作为参数，并生成一个在此范围之间的随机数。</p><p>范围表达式使用 <code>start..=end</code> 这样的形式，如 <code>1..=100</code> 就代表 1 到 100 之间。</p><div class="info custom-block"><p class="custom-block-title">INFO</p><p>你不可能凭空知道应当 use 哪个 trait，以及应当从 crate 中调用哪个方法，因此每个 crate 都有说明文档。 通过调用 <code>cargo doc --open</code> 来构建所有本地依赖提供的文档并在浏览器中打开。</p></div><h3 id="对比两个数字" tabindex="-1">对比两个数字 <a class="header-anchor" href="#对比两个数字" aria-label="Permalink to &quot;对比两个数字&quot;">​</a></h3><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 此代码不可运行</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> rand</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Rng</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> std</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cmp</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Ordering</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> std</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">io;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // --snip--</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You guessed: {guess}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> match</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cmp</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">secret_number) {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Ordering</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Less</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Too small!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Ordering</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Greater</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Too big!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Ordering</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Equal</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You win!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br></div></div><p>我们引入 <code>std::cmp::Ordering</code> 到作用域中。<code>Ordering</code> 也是一个枚举，其成员包含 <code>Less</code>、<code>Greater</code> 和 <code>Equal</code>，这是在两个值进行比较时可能出现的三种结果。</p><p><code>cmp</code> 方法用于比较两个值，并且<strong>可以在任何可比较的值上调用</strong>。它获取一个被比较值的引用：将 <code>guess</code> 与 <code>secret_number</code> 作比较。然后返回一个通过 <code>use</code> 引入作用域的 <code>Ordering</code> 枚举的成员。</p><p>使用 <code>match</code> 表达式，根据对 <code>guess</code> 和 <code>secret_number</code> 调用 <code>cmp</code> 返回的 <code>Ordering</code> 成员，来决定下一步应该要做什么。</p><p><code>match</code> 表达式由众多的分支（arms）构成，每个分支都包含一个 pattern 以及 pattern 被匹配时要执行的代码。</p><p>尝试执行此代码，编译器会抛出错误：不匹配的类型（mismatched types）。Rust 有一个静态强类型系统，同时也有类型推断。</p><p>当我们写出 <code>let guess = String::new();</code> 时，Rust 会帮我们推断出 <code>guess</code> 变量应当是 <code>String</code> 类型。</p><p>而 <code>secret_number</code> 是 1 - 100 之间的数字类型，而符合这个要求（1~100之间）的数字，在 Rust 中有下面几种：</p><ul><li><code>i32</code> 32位数字；</li><li><code>u32</code> 32位无符号数字；</li><li><code>i64</code> 64位数字</li><li>等等 ...</li></ul><p>Rust 默认使用 <code>i32</code>，所以 Rust 默认为 <code>secret_number</code> 推断出的类型是 <code>i32</code>，导致了字符串与数字作对比的情况。</p><p>要将 <code>String</code> 转化为数字类型才能与 <code>secret_number</code> 作比较：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">trim</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">parse</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">expect</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Please type a number!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>上面的代码将重新声明 <code>guess</code> 变量，这个特性叫隐藏（Shadowing），通过 <code>guess.trim()</code> 去除字符串头尾的空白字符（如用户输入 5 并按下空格后，在 Unix 系统中 <code>guess</code> 的值为 <code>5\n</code>，在 Windows 系统中 <code>guess</code> 的值为 <code>5\r\n</code>）</p><p><code>guess.parse()</code> 方法会将字符串转换为其他类型，通过给 <code>guess</code> 显式指定类型来告诉 <code>guess</code> 方法转化的目标类型，这里的目标类型是 <code>u32</code>。</p><p>同时，为了防止字符串中包含特殊字符等原因导致 <code>parse</code> 执行失败，这里用 <code>expect</code> 来对转化是否成功进行提示：</p><ul><li>如果 <code>parse</code> 不能从字符串生成一个数字，返回一个 <code>Result</code> 的 <code>Err</code> 成员时，<code>expect</code> 方法会使程序结束并打印附加的信息。</li><li>如果 <code>parse</code> 成功执行，那么它会返回 <code>Result</code> 的 <code>Ok</code> 成员，然后 <code>expect</code> 会返回 <code>Ok</code> 值中的数字。</li></ul><h3 id="使用循环来允许多次猜测" tabindex="-1">使用循环来允许多次猜测 <a class="header-anchor" href="#使用循环来允许多次猜测" aria-label="Permalink to &quot;使用循环来允许多次猜测&quot;">​</a></h3><p>可以使用 <code>loop</code> 关键字来创建一个无限循环，给用户更多机会来猜数。</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;The secret number is: {secret_number}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> loop</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Please input your guess.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // --snip--</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> match</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">cmp</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">secret_number) {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Ordering</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Less</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Too small!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Ordering</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Greater</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Too big!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Ordering</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Equal</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You win!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> break</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> },</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br></div></div><p>当用户成功猜对后，会执行 <code>break;</code> 退出程序。</p><h3 id="忽略非数字的猜测并继续游戏" tabindex="-1">忽略非数字的猜测并继续游戏 <a class="header-anchor" href="#忽略非数字的猜测并继续游戏" aria-label="Permalink to &quot;忽略非数字的猜测并继续游戏&quot;">​</a></h3><p>目前的代码如果用户输入了非数字，会导致 <code>parse</code> 失败，进而导致程序退出，因此我们需要改写这部分的逻辑，将 <code>expect</code> 调用 改为 <code>match</code>：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // --snip--</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> io</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">stdin</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">read_line</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">expect</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Failed to read line&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> match</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">trim</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">parse</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Ok</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(num) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> num,</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Err</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(_) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=&gt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> continue</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;You guessed: {guess}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // --snip--</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><p>这样当遇到错误时程序不再崩溃，而是进入到 <code>match</code> 的错误分支中处理错误：调用 <code>continue;</code> 继续循环。</p><h3 id="总结" tabindex="-1">总结 <a class="header-anchor" href="#总结" aria-label="Permalink to &quot;总结&quot;">​</a></h3><p>这一章里我们学习了使用 <code>let</code> 声明变量、变量隐藏、类型转化、<code>match</code> 处理多分支任务、<code>loop</code> 循环。</p><p>还学习了外部 crate 的使用、如何指定数据类型等</p><h2 id="常见编程概念" tabindex="-1">常见编程概念 <a class="header-anchor" href="#常见编程概念" aria-label="Permalink to &quot;常见编程概念&quot;">​</a></h2><h3 id="变量和可变性" tabindex="-1">变量和可变性 <a class="header-anchor" href="#变量和可变性" aria-label="Permalink to &quot;变量和可变性&quot;">​</a></h3><p>变量默认是不可变的（Immutable），这是 Rust 提供的众多特性之一：</p><p>下面的代码由于修改了 <code>x</code> 导致编译不通过：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;x is {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, x);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 6</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;x is {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, x);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>编译器抛出的错误信息：cannot assign twice to immutable variable <code>x</code></p><p>要让 <code>x</code> 变得可变，可以在声明 <code>let</code> 后添加 <code>mut</code>：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>这样就可以修改 <code>x</code> 的值了。</p><p>除了 <code>let</code>，还可以通过 <code>const</code> 声明一个常量：</p><ul><li>常量总是不可变，且不允许对常量使用 <code>mut</code></li><li>必须在声明时注明值的类型</li><li>常量只能被设置为常量表达式，而不是任何只能在运行时计算出的值</li></ul><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">const</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> THREE_HOURS_IN_SECONDS</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 60</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> *</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 60</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> *</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>这里的 <code>60 * 60 * 3</code> 会在编译器编译时执行运算，这使我们可以选择更容易理解和验证的方式来写出这个值，而不是直接将常量设置为 <code>10,800</code>。</p><p>在前文中我们介绍了变量隐藏，后声明的同名变量将会屏蔽掉之前声明的变量，直到新的变量也被隐藏或作用域结束：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 5</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 6</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">*</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;x is {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, x); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 12</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;x is {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, x); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 6</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><p>需要注意的是，隐藏与将变量标记为 <code>mut</code> 是有区别的，当对变量进行重新赋值时，如果没有使用 <code>mut</code> 那么会导致编译时错误。通过变量隐藏，我们可以用新的变量进行一些计算，但计算完之后变量依然是不可变的。</p><p><code>mut</code> 与隐藏的另一个区别是：当再次使用 <code>let</code> 声明变量时，隐藏实际上创建了一个新的变量，我们可以改变值的类型，只不过复用这个名字：</p><p>如果没有变量隐藏，代码可能会像这样：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces_str </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot; &quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces_num </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces_str</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">len</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>利用变量隐藏，我们可以简单地复用相同变量名：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot; &quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 文本之间的空格数量</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">len</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 多少个空格</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>然而，如果使用 <code>mut</code>，他不允许修改变量的类型：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot; &quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">spaces </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> spaces</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">len</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 错误：不能改变变量的类型</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="数据类型" tabindex="-1">数据类型 <a class="header-anchor" href="#数据类型" aria-label="Permalink to &quot;数据类型&quot;">​</a></h3><p>在 Rust 中，每一个值都属于某一种数据类型（data type），这告诉 Rust 它被指定为何种数据。</p><p>Rust 是静态类型（statically typed）语言编译时必须知道所有变量的类型，当多种类型均有可能时，例如使用 <code>parse</code> 将 <code>String</code> 转换为数字时，必须增加类型注解，像这样：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> guess</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;42&quot;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">parse</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">expect</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Not a number!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>在 Rust 中有两种数据类型子集：标量和复合</p><h4 id="标量类型-scalar" tabindex="-1">标量类型（scalar） <a class="header-anchor" href="#标量类型-scalar" aria-label="Permalink to &quot;标量类型（scalar）&quot;">​</a></h4><h5 id="整型" tabindex="-1">整型 <a class="header-anchor" href="#整型" aria-label="Permalink to &quot;整型&quot;">​</a></h5><p>整型是一个没有小数部分的数字，例如 <code>u32</code> 代表一个占据 32 bit 的无符号整数。其中<strong>有符号</strong>和<strong>无符号</strong>代表数字能否为负值。</p><table><thead><tr><th>长度</th><th>有符号</th><th>无符号</th></tr></thead><tbody><tr><td>8-bit</td><td>i8</td><td>u8</td></tr><tr><td>16-bit</td><td>i16</td><td>u16</td></tr><tr><td>32-bit</td><td>i32</td><td>u32</td></tr><tr><td>64-bit</td><td>i64</td><td>u64</td></tr><tr><td>128-bit</td><td>i128</td><td>u128</td></tr><tr><td>arch</td><td>isize</td><td>usize</td></tr></tbody></table><p>有符号的整型可以存储从 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.566ex;" xmlns="http://www.w3.org/2000/svg" width="7.844ex" height="2.452ex" role="img" focusable="false" viewBox="0 -833.9 3466.9 1083.9" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mo"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mo" transform="translate(778,0)"><path data-c="28" d="M94 250Q94 319 104 381T127 488T164 576T202 643T244 695T277 729T302 750H315H319Q333 750 333 741Q333 738 316 720T275 667T226 581T184 443T167 250T184 58T225 -81T274 -167T316 -220T333 -241Q333 -250 318 -250H315H302L274 -226Q180 -141 137 -14T94 250Z" style="stroke-width:3;"></path></g><g data-mml-node="msup" transform="translate(1167,0)"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315T301 241Q265 210 201 149L142 93L218 92Q375 92 385 97Q392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19V31Q50 38 56 46T86 81Q115 113 136 137Q145 147 170 174T204 211T233 244T261 278T284 308T305 340T320 369T333 401T340 431T343 464Q343 527 309 573T212 619Q179 619 154 602T119 569T109 550Q109 549 114 549Q132 549 151 535T170 489Q170 464 154 447T109 429Z" style="stroke-width:3;"></path></g><g data-mml-node="TeXAtom" transform="translate(533,363) scale(0.707)" data-mjx-texclass="ORD"><g data-mml-node="mi"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341T56 388T89 425T135 442Q171 442 195 424T225 390T231 369Q231 367 232 367L243 378Q304 442 382 442Q436 442 469 415T503 336T465 179T427 52Q427 26 444 26Q450 26 453 27Q482 32 505 65T540 145Q542 153 560 153Q580 153 580 145Q580 144 576 130Q568 101 554 73T508 17T439 -10Q392 -10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291L189 157Q156 26 151 16Q138 -11 108 -11Q95 -11 87 -5T76 7T74 17Q74 30 112 180T152 343Q153 348 153 366Q153 405 129 405Q91 405 66 305Q60 285 60 284Q58 278 41 278H27Q21 284 21 287Z" style="stroke-width:3;"></path></g><g data-mml-node="mo" transform="translate(600,0)"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(1378,0)"><path data-c="31" d="M213 578L200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641T273 663Q275 666 285 666Q294 666 302 660V361L303 61Q310 54 315 52T339 48T401 46H427V0H416Q395 3 257 3Q121 3 100 0H88V46H114Q136 46 152 46T177 47T193 50T201 52T207 57T213 61V578Z" style="stroke-width:3;"></path></g></g></g><g data-mml-node="mo" transform="translate(3077.9,0)"><path data-c="29" d="M60 749L64 750Q69 750 74 750H86L114 726Q208 641 251 514T294 250Q294 182 284 119T261 12T224 -76T186 -143T145 -194T113 -227T90 -246Q87 -249 86 -250H74Q66 -250 63 -250T58 -247T55 -238Q56 -237 66 -225Q221 -64 221 250T66 725Q56 737 55 738Q55 746 60 749Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>−</mo><mo stretchy="false">(</mo><msup><mn>2</mn><mrow data-mjx-texclass="ORD"><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup><mo stretchy="false">)</mo></math></mjx-assistive-mml></mjx-container> 到 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.186ex;" xmlns="http://www.w3.org/2000/svg" width="8.22ex" height="2.072ex" role="img" focusable="false" viewBox="0 -833.9 3633.4 915.9" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315T301 241Q265 210 201 149L142 93L218 92Q375 92 385 97Q392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19V31Q50 38 56 46T86 81Q115 113 136 137Q145 147 170 174T204 211T233 244T261 278T284 308T305 340T320 369T333 401T340 431T343 464Q343 527 309 573T212 619Q179 619 154 602T119 569T109 550Q109 549 114 549Q132 549 151 535T170 489Q170 464 154 447T109 429Z" style="stroke-width:3;"></path></g><g data-mml-node="TeXAtom" transform="translate(533,363) scale(0.707)" data-mjx-texclass="ORD"><g data-mml-node="mi"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341T56 388T89 425T135 442Q171 442 195 424T225 390T231 369Q231 367 232 367L243 378Q304 442 382 442Q436 442 469 415T503 336T465 179T427 52Q427 26 444 26Q450 26 453 27Q482 32 505 65T540 145Q542 153 560 153Q580 153 580 145Q580 144 576 130Q568 101 554 73T508 17T439 -10Q392 -10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291L189 157Q156 26 151 16Q138 -11 108 -11Q95 -11 87 -5T76 7T74 17Q74 30 112 180T152 343Q153 348 153 366Q153 405 129 405Q91 405 66 305Q60 285 60 284Q58 278 41 278H27Q21 284 21 287Z" style="stroke-width:3;"></path></g><g data-mml-node="mo" transform="translate(600,0)"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(1378,0)"><path data-c="31" d="M213 578L200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641T273 663Q275 666 285 666Q294 666 302 660V361L303 61Q310 54 315 52T339 48T401 46H427V0H416Q395 3 257 3Q121 3 100 0H88V46H114Q136 46 152 46T177 47T193 50T201 52T207 57T213 61V578Z" style="stroke-width:3;"></path></g></g></g><g data-mml-node="mo" transform="translate(2133.2,0)"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(3133.4,0)"><path data-c="31" d="M213 578L200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641T273 663Q275 666 285 666Q294 666 302 660V361L303 61Q310 54 315 52T339 48T401 46H427V0H416Q395 3 257 3Q121 3 100 0H88V46H114Q136 46 152 46T177 47T193 50T201 52T207 57T213 61V578Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mn>2</mn><mrow data-mjx-texclass="ORD"><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msup><mo>−</mo><mn>1</mn></math></mjx-assistive-mml></mjx-container> 在内的数字，这里的 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.025ex;" xmlns="http://www.w3.org/2000/svg" width="1.357ex" height="1.025ex" role="img" focusable="false" viewBox="0 -442 600 453" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mi"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341T56 388T89 425T135 442Q171 442 195 424T225 390T231 369Q231 367 232 367L243 378Q304 442 382 442Q436 442 469 415T503 336T465 179T427 52Q427 26 444 26Q450 26 453 27Q482 32 505 65T540 145Q542 153 560 153Q580 153 580 145Q580 144 576 130Q568 101 554 73T508 17T439 -10Q392 -10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291L189 157Q156 26 151 16Q138 -11 108 -11Q95 -11 87 -5T76 7T74 17Q74 30 112 180T152 343Q153 348 153 366Q153 405 129 405Q91 405 66 305Q60 285 60 284Q58 278 41 278H27Q21 284 21 287Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>n</mi></math></mjx-assistive-mml></mjx-container> 代表位数。</p><p>例如 <code>i8</code> 可以存储 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.566ex;" xmlns="http://www.w3.org/2000/svg" width="5.639ex" height="2.468ex" role="img" focusable="false" viewBox="0 -841 2492.6 1091" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mo"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mo" transform="translate(778,0)"><path data-c="28" d="M94 250Q94 319 104 381T127 488T164 576T202 643T244 695T277 729T302 750H315H319Q333 750 333 741Q333 738 316 720T275 667T226 581T184 443T167 250T184 58T225 -81T274 -167T316 -220T333 -241Q333 -250 318 -250H315H302L274 -226Q180 -141 137 -14T94 250Z" style="stroke-width:3;"></path></g><g data-mml-node="msup" transform="translate(1167,0)"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315T301 241Q265 210 201 149L142 93L218 92Q375 92 385 97Q392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19V31Q50 38 56 46T86 81Q115 113 136 137Q145 147 170 174T204 211T233 244T261 278T284 308T305 340T320 369T333 401T340 431T343 464Q343 527 309 573T212 619Q179 619 154 602T119 569T109 550Q109 549 114 549Q132 549 151 535T170 489Q170 464 154 447T109 429Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="37" d="M55 458Q56 460 72 567L88 674Q88 676 108 676H128V672Q128 662 143 655T195 646T364 644H485V605L417 512Q408 500 387 472T360 435T339 403T319 367T305 330T292 284T284 230T278 162T275 80Q275 66 275 52T274 28V19Q270 2 255 -10T221 -22Q210 -22 200 -19T179 0T168 40Q168 198 265 368Q285 400 349 489L395 552H302Q128 552 119 546Q113 543 108 522T98 479L95 458V455H55V458Z" style="stroke-width:3;"></path></g></g><g data-mml-node="mo" transform="translate(2103.6,0)"><path data-c="29" d="M60 749L64 750Q69 750 74 750H86L114 726Q208 641 251 514T294 250Q294 182 284 119T261 12T224 -76T186 -143T145 -194T113 -227T90 -246Q87 -249 86 -250H74Q66 -250 63 -250T58 -247T55 -238Q56 -237 66 -225Q221 -64 221 250T66 725Q56 737 55 738Q55 746 60 749Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>−</mo><mo stretchy="false">(</mo><msup><mn>2</mn><mn>7</mn></msup><mo stretchy="false">)</mo></math></mjx-assistive-mml></mjx-container> 到 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.186ex;" xmlns="http://www.w3.org/2000/svg" width="6.016ex" height="2.088ex" role="img" focusable="false" viewBox="0 -841 2659 923" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315T301 241Q265 210 201 149L142 93L218 92Q375 92 385 97Q392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19V31Q50 38 56 46T86 81Q115 113 136 137Q145 147 170 174T204 211T233 244T261 278T284 308T305 340T320 369T333 401T340 431T343 464Q343 527 309 573T212 619Q179 619 154 602T119 569T109 550Q109 549 114 549Q132 549 151 535T170 489Q170 464 154 447T109 429Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="37" d="M55 458Q56 460 72 567L88 674Q88 676 108 676H128V672Q128 662 143 655T195 646T364 644H485V605L417 512Q408 500 387 472T360 435T339 403T319 367T305 330T292 284T284 230T278 162T275 80Q275 66 275 52T274 28V19Q270 2 255 -10T221 -22Q210 -22 200 -19T179 0T168 40Q168 198 265 368Q285 400 349 489L395 552H302Q128 552 119 546Q113 543 108 522T98 479L95 458V455H55V458Z" style="stroke-width:3;"></path></g></g><g data-mml-node="mo" transform="translate(1158.8,0)"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(2159,0)"><path data-c="31" d="M213 578L200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641T273 663Q275 666 285 666Q294 666 302 660V361L303 61Q310 54 315 52T339 48T401 46H427V0H416Q395 3 257 3Q121 3 100 0H88V46H114Q136 46 152 46T177 47T193 50T201 52T207 57T213 61V578Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mn>2</mn><mn>7</mn></msup><mo>−</mo><mn>1</mn></math></mjx-assistive-mml></mjx-container> 在内的数字，也就是从 -128 到 127。</p><p>无符号的整型可以存储从 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.05ex;" xmlns="http://www.w3.org/2000/svg" width="1.131ex" height="1.557ex" role="img" focusable="false" viewBox="0 -666 500 688" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mn"><path data-c="30" d="M96 585Q152 666 249 666Q297 666 345 640T423 548Q460 465 460 320Q460 165 417 83Q397 41 362 16T301 -15T250 -22Q224 -22 198 -16T137 16T82 83Q39 165 39 320Q39 494 96 585ZM321 597Q291 629 250 629Q208 629 178 597Q153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16Q290 16 318 46Q347 76 354 130T362 333Q362 478 354 524T321 597Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn></math></mjx-assistive-mml></mjx-container> 到 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.186ex;" xmlns="http://www.w3.org/2000/svg" width="6.176ex" height="1.714ex" role="img" focusable="false" viewBox="0 -675.5 2729.7 757.5" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315T301 241Q265 210 201 149L142 93L218 92Q375 92 385 97Q392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19V31Q50 38 56 46T86 81Q115 113 136 137Q145 147 170 174T204 211T233 244T261 278T284 308T305 340T320 369T333 401T340 431T343 464Q343 527 309 573T212 619Q179 619 154 602T119 569T109 550Q109 549 114 549Q132 549 151 535T170 489Q170 464 154 447T109 429Z" style="stroke-width:3;"></path></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341T56 388T89 425T135 442Q171 442 195 424T225 390T231 369Q231 367 232 367L243 378Q304 442 382 442Q436 442 469 415T503 336T465 179T427 52Q427 26 444 26Q450 26 453 27Q482 32 505 65T540 145Q542 153 560 153Q580 153 580 145Q580 144 576 130Q568 101 554 73T508 17T439 -10Q392 -10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291L189 157Q156 26 151 16Q138 -11 108 -11Q95 -11 87 -5T76 7T74 17Q74 30 112 180T152 343Q153 348 153 366Q153 405 129 405Q91 405 66 305Q60 285 60 284Q58 278 41 278H27Q21 284 21 287Z" style="stroke-width:3;"></path></g></g><g data-mml-node="mo" transform="translate(1229.5,0)"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(2229.7,0)"><path data-c="31" d="M213 578L200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641T273 663Q275 666 285 666Q294 666 302 660V361L303 61Q310 54 315 52T339 48T401 46H427V0H416Q395 3 257 3Q121 3 100 0H88V46H114Q136 46 152 46T177 47T193 50T201 52T207 57T213 61V578Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mn>2</mn><mi>n</mi></msup><mo>−</mo><mn>1</mn></math></mjx-assistive-mml></mjx-container>的数字。</p><p>所以 <code>u8</code> 可以存储 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.05ex;" xmlns="http://www.w3.org/2000/svg" width="1.131ex" height="1.557ex" role="img" focusable="false" viewBox="0 -666 500 688" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mn"><path data-c="30" d="M96 585Q152 666 249 666Q297 666 345 640T423 548Q460 465 460 320Q460 165 417 83Q397 41 362 16T301 -15T250 -22Q224 -22 198 -16T137 16T82 83Q39 165 39 320Q39 494 96 585ZM321 597Q291 629 250 629Q208 629 178 597Q153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16Q290 16 318 46Q347 76 354 130T362 333Q362 478 354 524T321 597Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><mn>0</mn></math></mjx-assistive-mml></mjx-container> 到 <mjx-container class="MathJax" jax="SVG" style="direction:ltr;position:relative;"><svg style="overflow:visible;min-height:1px;min-width:1px;vertical-align:-0.186ex;" xmlns="http://www.w3.org/2000/svg" width="6.016ex" height="2.072ex" role="img" focusable="false" viewBox="0 -833.9 2659 915.9" aria-hidden="true"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315T301 241Q265 210 201 149L142 93L218 92Q375 92 385 97Q392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19V31Q50 38 56 46T86 81Q115 113 136 137Q145 147 170 174T204 211T233 244T261 278T284 308T305 340T320 369T333 401T340 431T343 464Q343 527 309 573T212 619Q179 619 154 602T119 569T109 550Q109 549 114 549Q132 549 151 535T170 489Q170 464 154 447T109 429Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="38" d="M70 417T70 494T124 618T248 666Q319 666 374 624T429 515Q429 485 418 459T392 417T361 389T335 371T324 363L338 354Q352 344 366 334T382 323Q457 264 457 174Q457 95 399 37T249 -22Q159 -22 101 29T43 155Q43 263 172 335L154 348Q133 361 127 368Q70 417 70 494ZM286 386L292 390Q298 394 301 396T311 403T323 413T334 425T345 438T355 454T364 471T369 491T371 513Q371 556 342 586T275 624Q268 625 242 625Q201 625 165 599T128 534Q128 511 141 492T167 463T217 431Q224 426 228 424L286 386ZM250 21Q308 21 350 55T392 137Q392 154 387 169T375 194T353 216T330 234T301 253T274 270Q260 279 244 289T218 306L210 311Q204 311 181 294T133 239T107 157Q107 98 150 60T250 21Z" style="stroke-width:3;"></path></g></g><g data-mml-node="mo" transform="translate(1158.8,0)"><path data-c="2212" d="M84 237T84 250T98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z" style="stroke-width:3;"></path></g><g data-mml-node="mn" transform="translate(2159,0)"><path data-c="31" d="M213 578L200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641T273 663Q275 666 285 666Q294 666 302 660V361L303 61Q310 54 315 52T339 48T401 46H427V0H416Q395 3 257 3Q121 3 100 0H88V46H114Q136 46 152 46T177 47T193 50T201 52T207 57T213 61V578Z" style="stroke-width:3;"></path></g></g></g></svg><mjx-assistive-mml unselectable="on" display="inline" style="top:0px;left:0px;clip:rect(1px, 1px, 1px, 1px);-webkit-touch-callout:none;-webkit-user-select:none;-khtml-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;position:absolute;padding:1px 0px 0px 0px;border:0px;display:block;width:auto;overflow:hidden;"><math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mn>2</mn><mn>8</mn></msup><mo>−</mo><mn>1</mn></math></mjx-assistive-mml></mjx-container> 的数字，也就是 0 到 255。</p><p>另外，<code>isize</code> 与 <code>usize</code> 类型依赖运行程序的计算机架构：在 64 位架构上，它们是 64 位的，在 32 位架构上，它们是 32 位的。分别等价于 <code>i64</code> <code>i32</code> 与 <code>u64</code> 和 <code>u32</code>。</p><p>除了通过类型指定变量的整型类型，还可以以后缀形式使用类型，例如 <code>let x = 57u8;</code>。还可以通过数字字面值来指定类型：</p><p><code>1000</code> 与 <code>1_000</code> 等价，但后者更易读。</p><table><thead><tr><th>数字字面值</th><th>例子</th></tr></thead><tbody><tr><td>Decimal (十进制)</td><td>98_222</td></tr><tr><td>Hex (十六进制)</td><td>0xff</td></tr><tr><td>Octal (八进制)</td><td>0o77</td></tr><tr><td>Binary (二进制)</td><td>0b1111_0000</td></tr><tr><td>Byte (单字节字符)(仅限于u8)</td><td>b&#39;A&#39;</td></tr></tbody></table><h5 id="浮点型" tabindex="-1">浮点型 <a class="header-anchor" href="#浮点型" aria-label="Permalink to &quot;浮点型&quot;">​</a></h5><p>在 Rust 中有两个原生浮点数类型：</p><ul><li><code>f32</code> 单精度浮点数，占 32 位</li><li><code>f64</code> 双精度浮点数，占 64 位，现代 CPU 中，它与 <code>f32</code> 速度几乎一样，不过精度更高</li></ul><p>浮点数都是有符号的。</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 2.0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// f64</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> y</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> f32</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 3.0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// f32</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>Rust 中的所有数字类型都支持基本数学运算：加法、减法、乘法、除法和取余。整数除法会向零舍入到最接近的整数：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // addition</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sum </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> +</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // subtraction</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> difference </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 95.5</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> -</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 4.3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // multiplication</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> product </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 4</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> *</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // division</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> quotient </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 56.7</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> /</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 32.2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> truncated </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> -</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> /</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 结果为 -1</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // remainder</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> remainder </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 43</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> %</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br></div></div><h5 id="布尔型" tabindex="-1">布尔型 <a class="header-anchor" href="#布尔型" aria-label="Permalink to &quot;布尔型&quot;">​</a></h5><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> t </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> f</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> bool</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> false</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h5 id="字符类型" tabindex="-1">字符类型 <a class="header-anchor" href="#字符类型" aria-label="Permalink to &quot;字符类型&quot;">​</a></h5><p>Rust 的 <code>char</code> 类型是语言最原生的字母类型，大小为四个字节：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> c </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &#39;z&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> z</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> char</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &#39;ℤ&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 显式类型声明</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> heart_eye_cat </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &#39;😻&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><h4 id="复合类型-compound" tabindex="-1">复合类型（compound） <a class="header-anchor" href="#复合类型-compound" aria-label="Permalink to &quot;复合类型（compound）&quot;">​</a></h4><p>复合类型（Compound types）可以将多个值组合成一个类型。Rust 有两个原生的复合类型：元组（tuple）和数组（array）。</p><h5 id="元组类型" tabindex="-1">元组类型 <a class="header-anchor" href="#元组类型" aria-label="Permalink to &quot;元组类型&quot;">​</a></h5><p>元组是一个将多个其他类型的值组合进一个复合类型的主要方式。元组长度固定：一旦声明，其长度不会增大或缩小。</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tup</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">f64</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">u8</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">500</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">6.4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>可以使用模式匹配（pattern matching）来解构（destructure）元组值：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tup </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">500</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">6.4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (x, y, z) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tup;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, y); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 6.4</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>也可以直接用 <code>.</code> 跟随值的索引来访问元组中的元素：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tup </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">500</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">6.4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> </span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tup</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> y </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tup</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> z </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> tup</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, x); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 500</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>不带任何值的元组有个特殊的名称，叫做 单元（unit） 元组。这种值以及对应的类型都写作 <code>()</code>，表示<strong>空值或空的返回类型</strong>。如果表达式不返回任何其他值，则会隐式返回单元值。</p><h5 id="数组类型" tabindex="-1">数组类型 <a class="header-anchor" href="#数组类型" aria-label="Permalink to &quot;数组类型&quot;">​</a></h5><p>与元组不同，数组中每个元素的类型必须相同。</p><p><strong>Rust 中的数组长度是固定的。</strong></p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>当你想要在栈（stack）而不是在堆（heap）上为数据分配空间（第四章将讨论栈与堆的更多内容），或者是想要确保总是有固定数量的元素时，数组非常有用。</p><p>但是数组并不如 <code>vector</code> 类型灵活。</p><p><code>vector</code> 类型是标准库提供的一个 允许 增长和缩小长度的类似数组的集合类型。当不确定是应该使用数组还是 vector 的时候，那么很可能应该使用 <code>vector</code>。</p><p>然而，当你<strong>确定元素个数不会改变时，数组会更有用</strong>。</p><p>例如，当你在一个程序中使用月份名字时，你更应趋向于使用数组而不是 <code>vector</code>，因为你确定只会有 12 个元素。</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> months </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;January&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;February&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;March&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;April&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;May&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;June&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;July&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;August&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;September&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;October&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;November&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;December&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>声明数组时，可以像这样编写数组的类型，既能约束数组中元素的类型，还能限制数组的长度：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">] </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>这里的 <code>i32</code> 代表每个元素的类型，分号之后的 <code>5</code> 代表数组的长度为 5，包含五个元素。</p><p>还可以在类型声明中指定初始值：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> b</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>这样变量 <code>b</code> 就是一个长度为 5，初始值全为 3 的数组。</p><p>数组是可以在栈 (stack) 上分配的已知固定大小的单个内存块。可以使用索引来访问数组的元素，像这样：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> c </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> c[</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">]; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 1</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> y </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> c[</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">]; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 2</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>通过索引从数组中取值的操作如果是在运行时进行的，那么代码可以顺利通过编译，但在运行时会出错：</p><p>下面这段代码可以正常通过编译，当你输入 0 1 2 3 4 访问数组时工作正常，但一旦输入了超过数组长度的索引如 10，就会抛出错误。</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">use</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> std</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">io;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Please enter an array index.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> index </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">new</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> io</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">stdin</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">read_line</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> index)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">expect</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Failed to read line&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> index</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> usize</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> index</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">trim</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">parse</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> .</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">expect</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Index entered was not a number&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> element </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a[index];</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;The value of the element at index {index} is: {element}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br></div></div><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">thread</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &#39;main&#39;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> panicked</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> at</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &#39;index out of bounds: the len is 5 but the index is 10&#39;,</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> src/main.rs:19:19</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">note:</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> run</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> with</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> `</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">RUST_BACKTRACE</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">` </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">environment</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> variable to display a backtrace</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="函数" tabindex="-1">函数 <a class="header-anchor" href="#函数" aria-label="Permalink to &quot;函数&quot;">​</a></h3><ul><li>必须显式指定参数的类型</li><li>通过 <code>-&gt;</code> 指定返回值的类型</li><li>函数结尾不包含分号时，隐式返回表达式</li></ul><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> print_labeled_measurement</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">188</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&#39;s&#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> f</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> i32</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> five</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;five: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, f);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> print_labeled_measurement</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(value</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, unit_label</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> char</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;The measurement is: {value}{unit_label}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> five</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 结尾不包含分号 隐式返回表达式</span></span>
<span class="line"><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><h3 id="控制流" tabindex="-1">控制流 <a class="header-anchor" href="#控制流" aria-label="Permalink to &quot;控制流&quot;">​</a></h3><h4 id="if-else-else-if" tabindex="-1">if-else &amp; else-if <a class="header-anchor" href="#if-else-else-if" aria-label="Permalink to &quot;if-else &amp; else-if&quot;">​</a></h4><ul><li>可以省略 if 与条件之间的空格</li><li>不允许隐式转换</li></ul><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&lt;</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Yes.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> } </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;No.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 不允许隐式转换 条件表达式必须返回一个布尔值</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Yes.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">!=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Yes.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p><code>if</code> 可以返回一个值，因此可以在 <code>let</code> 语句中使用 <code>if</code>：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> condition </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // if 与 else 分支的结果都为 i32</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> condition { </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> } </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> { </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">6</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;number: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, number);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>由于类型必须在编译时被确定，编译器会自动识别出不符合这一原则的 if-in-let 声明：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 编译报错 因为 if 与 else 分支的结果类型不同</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> condition { </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> } </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> { </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;six&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><h4 id="循环" tabindex="-1">循环 <a class="header-anchor" href="#循环" aria-label="Permalink to &quot;循环&quot;">​</a></h4><ul><li><code>break;</code> 用于中止循环</li><li><code>continue;</code> 用于跳过当次循环</li><li><code>break;</code> 可以从循环返回表达式</li></ul><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> result </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> loop</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> break</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">*</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;result: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, result); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 20</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>循环标签：在多个循环之间消除歧义</p><p>如果你存在一个嵌套的循环，而 <code>break;</code> 与 <code>continue;</code> 只会应用于此时最内层的循环，可以通过循环标签来让这些关键字应用于已标记的循环：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> &#39;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">counting_up</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> loop</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;count = {count}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> remaining </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> loop</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;remaining = {remaining}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> remaining </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 9</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> break</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> break</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> &#39;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">counting_up</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> remaining </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;End count = {count}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br></div></div><p>上面的代码中，第一个 <code>break;</code> 语句只会退出内层循环，而 <code>break &#39;counting_up&#39;;</code> 语句将直接退出外层循环。</p><p>除了 <code>loop</code>，Rust 还支持通过 <code>while</code> 来控制循环：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> while</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">!=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{number}!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;LIFTOFF!!!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p>当我们要实现遍历集合中的元素时，用 <code>for</code> 会更方便：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">20</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">40</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> for</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> element </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">in</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;value is {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, a);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p><code>for</code> 亦可用于计时：</p><p>这段代码中用到了 <code>.rev()</code> 方法来将 range 反转</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> for</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">in</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">..</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">4</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">rev</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{number}!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;LIFTOFF!!!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><h2 id="所有权" tabindex="-1">所有权 <a class="header-anchor" href="#所有权" aria-label="Permalink to &quot;所有权&quot;">​</a></h2><h3 id="什么是所有权" tabindex="-1">什么是所有权 <a class="header-anchor" href="#什么是所有权" aria-label="Permalink to &quot;什么是所有权&quot;">​</a></h3><p>Rust 的核心功能之一就是<strong>所有权</strong>（ownership）。</p><p>所有程序都必须管理其运行时使用计算机内存的方式：</p><ul><li>一些语言具有垃圾回收机制，在程序运行时有规律地寻找不再使用的内存；</li><li>在另一些语言中，程序员必须亲自分配和释放内存；</li><li>Rust 则选择了第三种方式，通过所有权系统管理内存</li></ul><p>编译器在编译时会根据一系列的规则进行检查，如果违反了任何这些规则，程序都不能编译。</p><ul><li>Rust 中每一个值都有一个所有者（owner）；</li><li>值在任一时刻只有且只有一个所有者；</li><li>当所有者（变量）离开作用域，这个值会被丢弃。</li></ul><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">{</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // s 尚未被声明 无法访问</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">; </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 在此处起 s 是有效的</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 声明后 在作用域内 你可以使用 s</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 作用域外 s 被销毁，使用 s 是不被允许的</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>在上面的代码中有两个重要的时间点：</p><ul><li>s <strong>进入作用域</strong>时，它是有效的</li><li>这一直持续到它<strong>离开作用域</strong>为止</li></ul><p>为了演示所有权的规则，我们需要引入一个存储在堆上的数据类型</p><p>之前由字符串字面量创建字符串时，在编译阶段就知道其内容，这部分内容被硬编码存储在最终的编译结果中。</p><p>但通过 <code>String</code> 创建的字符串，此类型管理被分配到堆上的数据，所以能够存储在编译时未知大小的文本：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>双冒号 <code>::</code> 是一种运算符，它允许将特定的 <code>from</code> 函数置于 <code>String</code> 类型的命名空间（namespace）下，而不需要使用如 <code>string_from</code> 这样的名字。</p><p>可以修改此类字符串：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">push_str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;, World!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 在 s 后追加字面值</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;s: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, s); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// &quot;Hello, World!&quot;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p>不同于通过字符串字面量创建的字符串，此类字符串可以被修改。这是因为两种类型在内存上的处理不同：</p><ul><li>通过字符串字面量创建的字符串：被硬编码进最终的可执行文件中，这使得字符串字面值快速且高效，但代价是它的不可变性。</li><li><code>String</code> 类型为了支持可变、可增长的文本片段，需要在堆上分配一块在编译时未知大小的内存来存放内容</li></ul><ol><li>必须在运行时向内存分配器（memory allocator）请求内存</li><li>需要一个当我们处理完 <code>String</code> 时将内存返回给分配器的方法</li></ol><p>对于 1. 我们已经通过 <code>String::from</code> 完成，然而对于 2. 在 Rust 中则是采用这样的策略：内存在拥有它的变量离开作用域时就被自动释放：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">{</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">} </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 作用域结束</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// 此时 s 不再有效</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>这是一个将 <code>String</code> 需要的内存返回给分配器的很自然的位置：当 <code>s</code> 离开作用域的时候。当变量离开作用域，Rust 为我们调用一个特殊的函数。这个函数叫做 <code>drop</code>，在这里 <code>String</code> 的作者可以放置释放内存的代码。Rust 在结尾的 <code>}</code> 处自动调用 <code>drop</code>。</p><p>以整型数据为例，同一数据可以被不同的变量绑定：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> y </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>将 <code>5</code> 绑定到变量 <code>x</code>，生成一个值 <code>x</code> 的拷贝并绑定到变量 <code>y</code> 上，因为整型是已知固定大小的简单值，所以两个 <code>5</code> 都被放入了栈中。</p><p>再举一个 <code>String</code> 版本的例子：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s2 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s1;</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>虽然做的事情是一样的，但内存分配上完全不同：</p><p><img src="/assets/trpl04-04.DJSrdqKd.svg" alt="s1被标记为无效的内存表现" loading="lazy"></p><ul><li>如果 <code>s1</code> 未被销毁，两个变量指向了同一个内存空间，存在二次释放的风险；</li><li>如果重新开辟新的内存空间被开辟，会带来性能问题；</li></ul><p>因此，当执行 <code>s2 = s1</code> 时，不会有新的内存空间被开辟，<code>s1</code> 被标记为无效，不再允许被使用，<code>s2</code> 是有效的，当其离开自己的作用域就释放自己的内存。</p><p>Rust 永远不会自动创建数据的“深拷贝”，因此任何自动的复制都会被认为是对运行时性能影响较小的。</p><p>如果我们确实需要深度复制 <code>String</code> 中堆上的数据，而不仅仅是栈上的数据，可以显式调用 <code>clone</code> 方法。</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s2 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s1</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">clone</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;s1: {}, s2: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, s1, s2); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// s1 与 s2 都可用</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><p>在 Rust 中有一种 <code>Copy</code> trait 的特殊注解：如果一个类型实现了 <code>Copy</code> trait，那么一个旧的变量在将其赋值给其他变量后仍然可用。</p><p><code>Drop</code> trait 与 <code>Copy</code> trait 是互斥的，一个通用的鉴别类型是不是实现了 Copy trait 的方法是：</p><p>任何一组简单标量值的组合都可以实现 <code>Copy</code>，任何不需要分配内存或某种形式资源的类型都可以实现 <code>Copy</code>，如：</p><p>int、bool、float、char、tuple</p><h3 id="引用与借用" tabindex="-1">引用与借用 <a class="header-anchor" href="#引用与借用" aria-label="Permalink to &quot;引用与借用&quot;">​</a></h3><h3 id="slice-类型" tabindex="-1">Slice 类型 <a class="header-anchor" href="#slice-类型" aria-label="Permalink to &quot;Slice 类型&quot;">​</a></h3><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> takes_ownership</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(s);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // s had been moved</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // println!(&quot;{}&quot;, s);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> makes_copy</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(x);</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, x); </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// x is still avaliable(copied)</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> takes_ownership</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(some_string</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, some_string);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> makes_copy</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(some_integer</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, some_integer);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> gives_ownership</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s2 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s3 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> takes_and_gives_back</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(s2);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // s2 不可访问 因其所有权已经转移给了 s3</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;s1: {}, s3: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, s1, s3);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 向外界授予所有权</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> gives_ownership</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> some_string </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;yours&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> some_string</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 获取所有权并向外授予</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> takes_and_gives_back</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(a_string</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a_string</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (s2, len) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> calculate_length</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(s1);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;length of {} is {}.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, s2, len);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 计算 String 的长度并归还所有权</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> calculate_length</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(some_string</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">usize</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> size </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> some_string</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">len</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (some_string, size)</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> len </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> calculate_length</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s1);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 将 s1 的指针传递给函数</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 所有权不会被转移 在调用函数后 s1 仍然可用</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;length of {} is {}.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, s1, len);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> calculate_length</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> usize</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">len</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> change</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> change</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(some_string</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 此处无法通过编译 因为借用的变量无法被修改</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // some_string.push_str(&quot;SomeStuff&quot;);</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;some_string: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, some_string);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> change</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s);</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 如果已经创建了一个变量的可变引用</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 就不能再创建对该变量的引用 这是为了防止 data race</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;s had been changed to: {}.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, s);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> </span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> change</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(some_string</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;mut</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> some_string</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">push_str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;SomeStuff&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 当然 在不同的作用域中 可以创建不同的可变引用</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> r1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> r1</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">push_str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;SomeStuff&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> r2 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> r2</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">push_str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;SomeStuff&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 但是 不能同时拥有不可变引用与可变引用，或同时拥有多个可变引用</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> _r1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s;</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // let r2 = &amp;mut s;</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // println!(&quot;r1: {}, r2: {}&quot;, r1, r2);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> _r1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s;</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // let r2 = &amp;mut s;</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // println!(&quot;r1: {}, r2: {}&quot;, r1, r2);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 只要保证「不同时」即可</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> r1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s;</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;r1: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, r1);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // r1 借用完毕 r2 可以正常引用并使用 s 的引用</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> r2 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s;</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;r2: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, r2);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 悬垂引用 (Dangling References)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> reference_to_nothing </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> dangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;reference_to_nothing: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, reference_to_nothing);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // fn dangle() -&gt; &amp;String {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // // 创建字符串 s</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // let s = String::from(&quot;&quot;);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // // 返回字符串的引用 &amp;s</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // &amp;s</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // } // 作用域结束 s 被丢弃 占据的内存被释放</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> dangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // 返回 String 后 所有权被移动出函数 因此值不会被释放</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> words </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello World!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> result </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> first_word</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">words);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;result: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, result);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> first_word</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> usize</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> bytes </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">as_bytes</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> for</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(i, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">item) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">in</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> bytes</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">iter</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">enumerate</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> item </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> b&#39; &#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> i;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">len</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello, World!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> hello </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s[</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">..</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> world </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s[</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">6</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">..</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">];</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;{}, {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, hello, world);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> words </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Hello, World!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> result </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> first_word</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">words);</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;result: {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, result);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> first_word</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> bytes </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> s</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">as_bytes</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> for</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (i, </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">item) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">in</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> bytes</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">iter</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">()</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">enumerate</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> item </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> b&#39; &#39;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s[</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">..</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">i];</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">s[</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">..</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">]</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span 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class="line-number">172</span><br><span class="line-number">173</span><br><span class="line-number">174</span><br><span class="line-number">175</span><br><span class="line-number">176</span><br><span class="line-number">177</span><br><span class="line-number">178</span><br><span class="line-number">179</span><br><span class="line-number">180</span><br><span class="line-number">181</span><br><span class="line-number">182</span><br><span class="line-number">183</span><br><span class="line-number">184</span><br><span class="line-number">185</span><br><span class="line-number">186</span><br><span class="line-number">187</span><br><span class="line-number">188</span><br><span class="line-number">189</span><br><span class="line-number">190</span><br></div></div><h2 id="结构体" tabindex="-1">结构体 <a class="header-anchor" href="#结构体" aria-label="Permalink to &quot;结构体&quot;">​</a></h2><p><code>struct</code> 是一个自定义数据类型，允许你包装和命名多个相关的值，从而形成一个有意义的组合。</p><h3 id="结构体的定义与初始化" tabindex="-1">结构体的定义与初始化 <a class="header-anchor" href="#结构体的定义与初始化" aria-label="Permalink to &quot;结构体的定义与初始化&quot;">​</a></h3><p>下面的代码定义了一个用于存储用户账号信息的结构体：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> active</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> bool</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> username</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> email</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sign_in_count</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u64</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>要使用它，需要将其实例化：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> user1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> active</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> username</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Ziu&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> email</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;ziu@email.com&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sign_in_count</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p>默认情况下结构体中的值是不可变的，如果要修改某个字段，需要将<strong>结构体实例标记为可变的</strong>（Rust 不允许将某一个字段标记为可变的），那么可以通过 <code>.</code> 语法对实例中的值做修改：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> mut</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> user1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> active</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> username</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Ziu&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> email</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;ziu@email.com&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sign_in_count</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> user1</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">sign_in_count </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p>可以通过字段初始化简写语法来创建实例：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> build_user</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(email</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, username</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> active</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> email,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> username,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sign_in_count</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p>用结构更新语法使用更少的代码来创建新 <code>User</code> 实例：</p><p>创建一个新的 <code>User</code> 实例 <code>user2</code>，其中 <code>email</code> 字段是新的值，其余字段来自 <code>user1</code>。</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> user2 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> email</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> String</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">::</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">from</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;user2@email.com&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">),</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> ..</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">user1</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><div class="warning custom-block"><p class="custom-block-title">WARNING</p><p>结构更新语法就像 <code>=</code> 赋值一样遵循所有权转移规则，在这个例子中，<code>user2</code> 被创建后我们就不能再使用 <code>user1</code> 了，这是因为 <code>user1</code> 的 <code>username</code> 字段中的 <code>String</code> 值被转移到了 <code>user2</code> 中。</p><p>如果我们给 <code>user2</code> 的 <code>username</code> 与 <code>email</code> 都赋新值，只有 <code>active</code> 和 <code>sign_in_count</code> 被复用，那么 <code>user1</code> 仍可用。</p></div><p>元组结构体（tuple structs）中可以通过 <code>struct</code> 关键字定义，但没有具体的字段名，只有字段的类型</p><p>当你想给元组取一个名字，并使元组成为与其他元组不同的类型时，元组结构体是很有用的：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Color</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Point</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">i32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> black </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Color</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> origin </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Point</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>没有任何字段的类单元结构体，类似于 <code>()</code> 即元祖类型中的 unit 类型。</p><p>常用语你想要在某个类型上实现 trait 但不需要在类型中存储数据时发挥作用。</p><p>声明并实例化一个名为 <code>AlwaysEqual</code> 的 unit 结构的例子：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> AlwaysEqual</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> subject </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> AlwaysEqual</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><div class="info custom-block"><p class="custom-block-title">INFO</p><p>结构体数据的所有权</p><p>前面 <code>User</code> 的例子中，<code>username</code> 与 <code>email</code> 字段都持有 <code>String</code> 类型的数据而不是其引用。</p><p>同时，结构体也可以存储被其他对象拥有的数据的引用，不过要这样做的话就必须引入<strong>生命周期</strong>这个概念。</p><p>生命周期确保结构体引用的数据有效性和结构体本身保持一致。如果你尝试在结构体中存储一个引用而不指定生命周期将是无效的：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> active</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> bool</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> username</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> email</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sign_in_count</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u64</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> user1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> User</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> active</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> username</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;someusername123&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> email</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;someone@example.com&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sign_in_count</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><p>执行编译时，编译器将会抛出错误：需要生命周期标识符</p></div><h3 id="示例" tabindex="-1">示例 <a class="header-anchor" href="#示例" aria-label="Permalink to &quot;示例&quot;">​</a></h3><p>下面写一个计算长方形面积的程序来理解何时需要使用结构体：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span></span>
<span class="line"><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;The area of the rectangle is {} square pixels.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> area</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(width, height)</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> );</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> area</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">*</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>通过元组给函数入参建立关联：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> rect1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span></span>
<span class="line"><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;The area of the rectangle is {} square pixels.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> area</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(rect1)</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> );</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> area</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(dimensions</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> dimensions</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> *</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> dimensions</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><p>用结构体给参数赋予更多意义，给参数添加语义化的标签：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> rect1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span></span>
<span class="line"><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;The area of the rectangle is {} square pixels.&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> area</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">rect1)</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> );</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> area</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(rectangle</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">-&gt;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> rectangle</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">width </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">*</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> rectangle</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">.</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">height</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br></div></div><p>借用结构体的所用权，将 <code>rect1</code> 的不可变引用传入 <code>area</code> 函数，通过 <code>.</code> 语法访问结构体字段不会移动字段的所有权。</p><p>在调试的过程中，如果你尝试将结构体通过 <code>println!</code> 宏打印，运行代码时会抛出错误：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> rect1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;rect1 is {}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, rect1);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">error[E0277]:</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> `</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Rectangle</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">`</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> doesn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">&#39;t implement `std::fmt::Display`</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p><code>println!</code> 宏能处理很多类型的格式，但当你使用 <code>{}</code> 占位符时，默认告诉 <code>println!</code> 使用被称为 <code>Display</code> 的格式：直接给终端用户查看的输出。</p><p>基本类型都默认实现了 <code>Display</code>，因为值很简单，Rust 可以帮我们完成这部分实现。然而对于结构体的展示存在很多细节：</p><ul><li>是否需要结尾的逗号？</li><li>需要打印出外层大括号吗？</li><li>所有字段都应该显示吗？</li></ul><p>因此 Rust 并没有在结构体上提供 <code>Display</code> 实现来使用 <code>println!</code> 与 <code>{}</code> 占位符。</p><p>你可以通过 <code>Debug</code> trait 输出格式打印结构体，将 <code>{}</code> 占位符替换为 <code>{:?}</code>：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;rect1 is {:?}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, rect1);</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>同时，我们必须显式地为结构体开启这个调试功能：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line highlighted"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">#[derive(</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Debug</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)]</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> rect1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 30</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;rect1 is {:?}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, rect1);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><p>这会默认展示所有的结构体中的字段：</p><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">rect1</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> is</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> Rectangle</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> {</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> width:</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> 30,</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> height:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 50</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> }</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>当结构体变得更大，有一种更易读的占位符可以使用：<code>{:#?}</code></p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> println!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;rect1 is {:#?}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, rect1);</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br></div></div><p>这包含了更漂亮的换行与缩进，输出的调试信息更易读。</p><p>另一种使用 <code>Debug</code> 格式打印数值的方法是 <code>dbg!</code> 宏，它接收一个表达式的所有权（与 <code>println!</code> 宏相反，后者接收的是引用）</p><p>打印出代码中调用 <code>dbg!</code> 宏时所在的文件和行号以及该表达式的结果值，并返回该值得所有权。</p><div class="warning custom-block"><p class="custom-block-title">WARNING</p><p>注意：调用 <code>dbg!</code> 宏会打印到标准错误控制台流（<code>stderr</code>），与 <code>println!</code> 不同，后者会打印到标准输出控制台流（<code>stdout</code>）。</p></div><p>下面是使用 <code>dbg!</code> 宏的例子：</p><div class="language-rs vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">rs</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">#[derive(</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">Debug</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)]</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">struct</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> u32</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">fn</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> main</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> scale </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> let</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> rect1 </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Rectangle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> width</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> dbg!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">30</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> *</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> scale),</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> height</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 50</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> };</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> dbg!</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&amp;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">rect1);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><div class="language-sh vp-adaptive-theme line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">sh</span><pre class="shiki shiki-themes github-light github-dark vp-code"><code><span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">$</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> cargo</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> run</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Compiling</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> rectangles</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> v0.1.0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (file:///projects/rectangles)</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Finished</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> dev</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> [unoptimized </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">+</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> debuginfo]</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> target</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">s</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">in</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> 0.61s</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> Running</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> `</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">target/debug/rectangles</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">`</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">[src/main.rs:10] </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">30</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> *</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> scale</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> =</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 60</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">[src/main.rs:14] &amp;</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">rect1</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> =</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> Rectangle</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> {</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> width:</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> 60,</span></span>
<span class="line"><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> height:</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> 50,</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><h3 id="方法语法" tabindex="-1">方法语法 <a class="header-anchor" href="#方法语法" aria-label="Permalink to &quot;方法语法&quot;">​</a></h3><p>在前面的代码中，<code>area</code> 函数是单独实现的，但实际上 <code>area</code> 函数与结构体 <code>Rectangle</code> 是强相关的。</p><p>这里涉及到 函数（function） 与 方法（method） 的不同：</p><p>与函数不同的是，方法是在结构体的上下文被定义的（或者是枚举或 trait 对象的上下文）</p><h2 id="枚举和模式匹配" tabindex="-1">枚举和模式匹配 <a class="header-anchor" href="#枚举和模式匹配" aria-label="Permalink to &quot;枚举和模式匹配&quot;">​</a></h2><h3 id="枚举的定义" tabindex="-1">枚举的定义 <a class="header-anchor" href="#枚举的定义" aria-label="Permalink to &quot;枚举的定义&quot;">​</a></h3><h3 id="match-控制流结构" tabindex="-1">match 控制流结构 <a class="header-anchor" href="#match-控制流结构" aria-label="Permalink to &quot;match 控制流结构&quot;">​</a></h3><h3 id="if-let-简洁控制流" tabindex="-1">if let 简洁控制流 <a class="header-anchor" href="#if-let-简洁控制流" aria-label="Permalink to &quot;if let 简洁控制流&quot;">​</a></h3></div></div></main><footer class="VPDocFooter" data-v-0ef3a6cc data-v-48e5664a><!--[--><!--]--><div class="edit-info" data-v-48e5664a><div class="edit-link" data-v-48e5664a><a class="VPLink link vp-external-link-icon no-icon edit-link-button" href="https://github.com/ZiuChen/ZiuChen.github.io/edit/main/docs/note/Rust.md" target="_blank" rel="noreferrer" data-v-48e5664a><!--[--><span class="vpi-square-pen edit-link-icon" data-v-48e5664a></span> Edit this page on GitHub<!--]--></a></div><div class="last-updated" data-v-48e5664a><p class="VPLastUpdated" data-v-48e5664a data-v-838bf1ba>Updated Date: <time datetime="2024-04-07T13:28:58.000Z" data-v-838bf1ba></time></p></div></div><nav class="prev-next" data-v-48e5664a><div class="pager" data-v-48e5664a><!----></div><div class="pager" data-v-48e5664a><a class="VPLink link pager-link next" href="/project/ClipboardManager/" data-v-48e5664a><!--[--><span class="desc" data-v-48e5664a>Next page</span><span class="title" data-v-48e5664a>超级剪贴板</span><!--]--></a></div></nav></footer><!--[--><!--]--></div></div></div><!--[--><!--]--></div></div><footer class="VPFooter has-sidebar" data-v-aa0dbd16 data-v-2e4bef11><div class="container" data-v-2e4bef11><p class="message" data-v-2e4bef11>Released under the MIT License.</p><p class="copyright" data-v-2e4bef11>Copyright © 2022-PRESENT ZiuChen</p></div></footer><!--[--><!--]--></div></div>
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