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<h1 id="元组"><a class="header" href="#元组">元组</a></h1>
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<p>元组是由多种类型组合到一起形成的，因此它是复合类型，元组的长度是固定的，元组中元素的顺序也是固定的。</p>
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<p>可以通过以下语法创建一个元组：</p>
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<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
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let tup: (i32, f64, u8) = (500, 6.4, 1);
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}</code></pre></pre>
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<p>变量 <code>tup</code> 被绑定了一个元组值 <code>(500, 6.4, 1)</code>，该元组的类型是 <code>(i32, f64, u8)</code>，看到没？元组是用括号将多个类型组合到一起，简单吧？</p>
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<p>可以使用模式匹配或者 <code>.</code> 操作符来获取元组中的值。</p>
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<h3 id="用模式匹配解构元组"><a class="header" href="#用模式匹配解构元组">用模式匹配解构元组</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
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let tup = (500, 6.4, 1);
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let (x, y, z) = tup;
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println!("The value of y is: {}", y);
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}</code></pre></pre>
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<p>上述代码首先创建一个元组，然后将其绑定到 <code>tup</code> 上，接着使用 <code>let (x, y, z) = tup;</code> 来完成一次模式匹配，因为元组是 <code>(n1, n2, n3)</code> 形式的，因此我们用一模一样的 <code>(x, y, z)</code> 形式来进行匹配，元组中对应的值会绑定到变量 <code>x</code>， <code>y</code>， <code>z</code>上。这就是解构：用同样的形式把一个复杂对象中的值匹配出来。</p>
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<h3 id="用--来访问元组"><a class="header" href="#用--来访问元组">用 <code>.</code> 来访问元组</a></h3>
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<p>模式匹配可以让我们一次性把元组中的值全部或者部分获取出来，如果只想要访问某个特定元素，那模式匹配就略显繁琐，对此，Rust 提供了 <code>.</code> 的访问方式：</p>
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<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
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let x: (i32, f64, u8) = (500, 6.4, 1);
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let five_hundred = x.0;
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let six_point_four = x.1;
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let one = x.2;
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}</code></pre></pre>
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<p>和其它语言的数组、字符串一样，元组的索引从 0 开始。</p>
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<h3 id="元组的使用示例"><a class="header" href="#元组的使用示例">元组的使用示例</a></h3>
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<p>元组在函数返回值场景很常用，例如下面的代码，可以使用元组返回多个值：</p>
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<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
|
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let s1 = String::from("hello");
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let (s2, len) = calculate_length(s1);
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println!("The length of '{}' is {}.", s2, len);
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}
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fn calculate_length(s: String) -> (String, usize) {
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let length = s.len(); // len() 返回字符串的长度
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(s, length)
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}</code></pre></pre>
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<p><code>calculate_length</code> 函数接收 <code>s1</code> 字符串的所有权，然后计算字符串的长度，接着把字符串所有权和字符串长度再返回给 <code>s2</code> 和 <code>len</code> 变量。</p>
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<p>在其他语言中，可以用结构体来声明一个三维空间中的点，例如 <code>Point(10, 20, 30)</code>，虽然使用 Rust 元组也可以做到：<code>(10, 20, 30)</code>，但是这样写有个非常重大的缺陷：</p>
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<p><strong>不具备任何清晰的含义</strong>，在下一章节中，会提到一种与元组类似的结构体，<code>元组结构体</code>，可以解决这个问题。</p>
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|
<h2 id="课后练习"><a class="header" href="#课后练习">课后练习</a></h2>
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<blockquote>
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|
<p><a href="https://practice-zh.course.rs/compound-types/tuple.html">Rust By Practice</a>，支持代码在线编辑和运行，并提供详细的<a href="https://github.com/sunface/rust-by-practice/blob/master/solutions/compound-types/tuple.md">习题解答</a>。</p>
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</blockquote>
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