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<h2 id="附录-a关键字"><a class="header" href="#附录-a关键字">附录 A：关键字</a></h2>
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<blockquote>
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<p><a href="https://github.com/rust-lang/book/blob/main/src/appendix-01-keywords.md">appendix-01-keywords.md</a>
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<br>
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commit efbafdba3618487fbc9305318fcab9775132ac15</p>
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</blockquote>
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<p>下面的列表包含 Rust 中正在使用或者以后会用到的关键字。因此，这些关键字不能被用作标识符（除了 “<a href="#%E5%8E%9F%E5%A7%8B%E6%A0%87%E8%AF%86%E7%AC%A6">原始标识符</a>” 部分介绍的原始标识符），这包括函数、变量、参数、结构体字段、模块、crate、常量、宏、静态值、属性、类型、trait 或生命周期
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的名字。</p>
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<h3 id="目前正在使用的关键字"><a class="header" href="#目前正在使用的关键字">目前正在使用的关键字</a></h3>
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<p>如下关键字目前有对应其描述的功能。</p>
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<ul>
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<li><code>as</code> - 强制类型转换，消除特定包含项的 trait 的歧义，或者对 <code>use</code> 语句中的项重命名</li>
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<li><code>async</code> - 返回一个 <code>Future</code> 而不是阻塞当前线程</li>
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<li><code>await</code> - 暂停执行直到 <code>Future</code> 的结果就绪</li>
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<li><code>break</code> - 立刻退出循环</li>
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<li><code>const</code> - 定义常量或不变裸指针（constant raw pointer）</li>
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<li><code>continue</code> - 继续进入下一次循环迭代</li>
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<li><code>crate</code> - 在模块路径中，代指 crate root</li>
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<li><code>dyn</code> - 动态分发 trait 对象</li>
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<li><code>else</code> - 作为 <code>if</code> 和 <code>if let</code> 控制流结构的 fallback</li>
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<li><code>enum</code> - 定义一个枚举</li>
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<li><code>extern</code> - 链接一个外部函数或变量</li>
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<li><code>false</code> - 布尔字面值 <code>false</code></li>
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<li><code>fn</code> - 定义一个函数或 <strong>函数指针类型</strong> (<em>function pointer type</em>)</li>
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<li><code>for</code> - 遍历一个迭代器或实现一个 trait 或者指定一个更高级的生命周期</li>
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<li><code>if</code> - 基于条件表达式的结果分支</li>
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<li><code>impl</code> - 实现自有或 trait 功能</li>
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<li><code>in</code> - <code>for</code> 循环语法的一部分</li>
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<li><code>let</code> - 绑定一个变量</li>
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<li><code>loop</code> - 无条件循环</li>
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<li><code>match</code> - 模式匹配</li>
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<li><code>mod</code> - 定义一个模块</li>
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<li><code>move</code> - 使闭包获取其所捕获项的所有权</li>
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<li><code>mut</code> - 表示引用、裸指针或模式绑定的可变性</li>
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<li><code>pub</code> - 表示结构体字段、<code>impl</code> 块或模块的公有可见性</li>
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<li><code>ref</code> - 通过引用绑定</li>
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<li><code>return</code> - 从函数中返回</li>
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<li><code>Self</code> - 定义或实现 trait 的类型的类型别名</li>
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<li><code>self</code> - 表示方法本身或当前模块</li>
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<li><code>static</code> - 表示全局变量或在整个程序执行期间保持其生命周期</li>
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<li><code>struct</code> - 定义一个结构体</li>
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<li><code>super</code> - 表示当前模块的父模块</li>
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<li><code>trait</code> - 定义一个 trait</li>
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<li><code>true</code> - 布尔字面值 <code>true</code></li>
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<li><code>type</code> - 定义一个类型别名或关联类型</li>
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<li><code>union</code> - 定义一个 <a href="https://doc.rust-lang.org/reference/items/unions.html">union</a> 并且是 union 声明中唯一用到的关键字</li>
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<li><code>unsafe</code> - 表示不安全的代码、函数、trait 或实现</li>
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<li><code>use</code> - 引入外部空间的符号</li>
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<li><code>where</code> - 表示一个约束类型的从句</li>
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<li><code>while</code> - 基于一个表达式的结果判断是否进行循环</li>
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</ul>
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<h3 id="保留做将来使用的关键字"><a class="header" href="#保留做将来使用的关键字">保留做将来使用的关键字</a></h3>
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<p>如下关键字没有任何功能，不过由 Rust 保留以备将来的应用。</p>
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<ul>
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<li><code>abstract</code></li>
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<li><code>become</code></li>
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<li><code>box</code></li>
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<li><code>do</code></li>
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<li><code>final</code></li>
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<li><code>macro</code></li>
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<li><code>override</code></li>
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<li><code>priv</code></li>
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<li><code>try</code></li>
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<li><code>typeof</code></li>
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<li><code>unsized</code></li>
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<li><code>virtual</code></li>
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<li><code>yield</code></li>
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</ul>
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<h3 id="原始标识符"><a class="header" href="#原始标识符">原始标识符</a></h3>
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<p>原始标识符（Raw identifiers）允许你使用通常不能使用的关键字，其带有 <code>r#</code> 前缀。</p>
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<p>例如，<code>match</code> 是关键字。如果尝试编译如下使用 <code>match</code> 作为名字的函数：</p>
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<pre><code class="language-rust ignore does_not_compile">fn match(needle: &str, haystack: &str) -> bool {
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haystack.contains(needle)
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}</code></pre>
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|
<p>会得到这个错误：</p>
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<pre><code class="language-text">error: expected identifier, found keyword `match`
|
|
|
--> src/main.rs:4:4
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4 | fn match(needle: &str, haystack: &str) -> bool {
|
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| ^^^^^ expected identifier, found keyword
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</code></pre>
|
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|
<p>该错误表示你不能将关键字 <code>match</code> 用作函数标识符。你可以使用原始标识符将 <code>match</code> 作为函数名称使用：</p>
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<p><span class="filename">文件名：src/main.rs</span></p>
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<pre><pre class="playground"><code class="language-rust edition2021">fn r#match(needle: &str, haystack: &str) -> bool {
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haystack.contains(needle)
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}
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fn main() {
|
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assert!(r#match("foo", "foobar"));
|
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}</code></pre></pre>
|
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<p>此代码编译没有任何错误。注意 <code>r#</code> 前缀需同时用于函数名定义和 <code>main</code> 函数中的调用。</p>
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<p>原始标识符允许使用你选择的任何单词作为标识符，即使该单词恰好是保留关键字。这给予了我们更大的自由来选择名字，这样与其他语言交互式就不用考虑到关键字问题，在要交互的语言中这个名字不是关键字。此外，原始标识符允许你使用以不同于你的 crate 使用的 Rust 版本编写的库。比如，<code>try</code> 在 2015 edition 中不是关键字，而在 2018 edition 则是。所以如果用 2015 edition 编写的库中带有 <code>try</code> 函数，在 2018 edition 中调用时就需要使用原始标识符语法，在这里是 <code>r#try</code>。有关版本的更多信息，请参见<a href="appendix-05-editions.html">附录 E</a>。</p>
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<script src="ferris.js"></script>
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</div>
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</body>
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</html>
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