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<main>
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<h1 id="疯狂字符串"><a class="header" href="#疯狂字符串">疯狂字符串</a></h1>
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<p>字符串让人疯狂,这句话用在 Rust 中一点都不夸张,不信?那你能否清晰的说出 <code>String</code>、<code>str</code>、<code>&str</code>、<code>&String</code>、<code>Box<str></code> 或 <code>Box<&str></code> 的区别?</p>
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<p>Rust 语言的类型可以大致分为两种:基本类型和标准库类型,前者是由语言特性直接提供的,而后者是在标准库中定义。即将登场的 <code>str</code> 类型就是唯一定义在语言特性中的字符串。</p>
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<blockquote>
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<p>在继续之前,大家需要先了解字符串的<a href="https://course.rs/basic/compound-type/string-slice.html">基本知识</a>,本文主要在于概念对比,而不是字符串讲解</p>
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</blockquote>
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<h2 id="str"><a class="header" href="#str">str</a></h2>
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<p>如上所述,<code>str</code> 是唯一定义在 Rust 语言特性中的字符串,但是也是我们几乎不会用到的字符串类型,为何?</p>
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<p>原因在于 <code>str</code> 字符串它是 <a href="https://course.rs/advance/into-types/sized.html#%E5%8A%A8%E6%80%81%E5%A4%A7%E5%B0%8F%E7%B1%BB%E5%9E%8B-dst"><code>DST</code> 动态大小类型</a>,这意味着编译器无法在编译期知道 <code>str</code> 类型的大小,只有到了运行期才能动态获知,这对于强类型、强安全的 Rust 语言来说是不可接受的。</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>let string: str = "banana";
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<span class="boring">}</span></code></pre></pre>
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<p>上面代码创建一个 <code>str</code> 类型的字符串,看起来很正常,但是编译就会报错:</p>
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<pre><code class="language-shell">error[E0277]: the size for values of type `str` cannot be known at compilation time
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--> src/main.rs:4:9
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4 | let string: str = "banana";
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| ^^^^^^ doesn't have a size known at compile-time
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</code></pre>
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<p>如果追求更深层的原因,我们可以总结如下:<strong>所有的切片都是动态类型,它们都无法直接被使用,而 <code>str</code> 就是字符串切片,<code>[u8]</code> 是数组切片。</strong></p>
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<p>同时还是 String 和 &str 的底层数据类型。 由于 str 是动态</p>
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<p><code>str</code> 类型是硬编码进可执行文件,也无法被修改,但是 <code>String</code> 则是一个可增长、可改变且具有所有权的 UTF-8 编码字符串,<strong>当 Rust 用户提到字符串时,往往指的就是 <code>String</code> 类型和 <code>&str</code> 字符串切片类型,这两个类型都是 UTF-8 编码</strong>。</p>
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<p>除了 <code>String</code> 类型的字符串,Rust 的标准库还提供了其他类型的字符串,例如 <code>OsString</code>, <code>OsStr</code>, <code>CsString</code> 和<code> CsStr</code> 等,注意到这些名字都以 <code>String</code> 或者 <code>Str</code> 结尾了吗?它们分别对应的是具有所有权和被借用的变量。</p>
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<p><strong>未完待续</strong></p>
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<p>https://pic1.zhimg.com/80/v2-177bce575bfaf289ae12d677689a26f4_1440w.png
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https://pic2.zhimg.com/80/v2-697ad53cb502ccec4b2e98c40975344f_1440w.png</p>
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<p>https://medium.com/@alisomay/strings-in-rust-28c08a2d3130</p>
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