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<ol class="chapter"><li class="chapter-item affix "><a href="../../about-book.html">关于本书</a></li><li class="chapter-item affix "><a href="../../into-rust.html">进入 Rust 编程世界</a></li><li class="chapter-item affix "><a href="../../first-try/sth-you-should-not-do.html">避免从入门到放弃</a></li><li class="chapter-item affix "><a href="../../community.html">社区和锈书</a></li><li class="spacer"></li><li class="chapter-item affix "><a href="../../some-thoughts.html">Datav: 可编程的数据可视化平台和可观测性平台</a></li><li class="chapter-item affix "><li class="part-title">Rust 语言基础学习</li><li class="spacer"></li><li class="chapter-item "><a href="../../first-try/intro.html"><strong aria-hidden="true">1.</strong> 寻找牛刀，以便小试</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../first-try/installation.html"><strong aria-hidden="true">1.1.</strong> 安装 Rust 环境</a></li><li class="chapter-item "><a href="../../first-try/editor.html"><strong aria-hidden="true">1.2.</strong> 墙推 VSCode!</a></li><li class="chapter-item "><a href="../../first-try/cargo.html"><strong aria-hidden="true">1.3.</strong> 认识 Cargo</a></li><li class="chapter-item "><a href="../../first-try/hello-world.html"><strong aria-hidden="true">1.4.</strong> 不仅仅是 Hello world</a></li><li class="chapter-item "><a href="../../first-try/slowly-downloading.html"><strong aria-hidden="true">1.5.</strong> 下载依赖太慢了？</a></li></ol></li><li class="chapter-item expanded "><a href="../../basic/intro.html"><strong aria-hidden="true">2.</strong> Rust 基础入门</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/variable.html"><strong aria-hidden="true">2.1.</strong> 变量绑定与解构</a></li><li class="chapter-item "><a href="../../basic/base-type/index.html"><strong aria-hidden="true">2.2.</strong> 基本类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/base-type/numbers.html"><strong aria-hidden="true">2.2.1.</strong> 数值类型</a></li><li class="chapter-item "><a href="../../basic/base-type/char-bool.html"><strong aria-hidden="true">2.2.2.</strong> 字符、布尔、单元类型</a></li><li class="chapter-item "><a href="../../basic/base-type/statement-expression.html"><strong aria-hidden="true">2.2.3.</strong> 语句与表达式</a></li><li class="chapter-item "><a href="../../basic/base-type/function.html"><strong aria-hidden="true">2.2.4.</strong> 函数</a></li></ol></li><li class="chapter-item "><a href="../../basic/ownership/index.html"><strong aria-hidden="true">2.3.</strong> 所有权和借用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/ownership/ownership.html"><strong aria-hidden="true">2.3.1.</strong> 所有权</a></li><li class="chapter-item "><a href="../../basic/ownership/borrowing.html"><strong aria-hidden="true">2.3.2.</strong> 引用与借用</a></li></ol></li><li class="chapter-item expanded "><a href="../../basic/compound-type/intro.html"><strong aria-hidden="true">2.4.</strong> 复合类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/compound-type/string-slice.html"><strong aria-hidden="true">2.4.1.</strong> 字符串与切片</a></li><li class="chapter-item "><a href="../../basic/compound-type/tuple.html"><strong aria-hidden="true">2.4.2.</strong> 元组</a></li><li class="chapter-item "><a href="../../basic/compound-type/struct.html"><strong aria-hidden="true">2.4.3.</strong> 结构体</a></li><li class="chapter-item "><a href="../../basic/compound-type/enum.html"><strong aria-hidden="true">2.4.4.</strong> 枚举</a></li><li class="chapter-item expanded "><a href="../../basic/compound-type/array.html" class="active"><strong aria-hidden="true">2.4.5.</strong> 数组</a></li></ol></li><li class="chapt
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<main>
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<h1 id="数组"><a class="header" href="#数组">数组</a></h1>
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<p>在日常开发中，使用最广的数据结构之一就是数组，在 Rust 中，最常用的数组有两种，第一种是速度很快但是长度固定的 <code>array</code>，第二种是可动态增长的但是有性能损耗的 <code>Vector</code>，在本书中，我们称 <code>array</code> 为数组，<code>Vector</code> 为动态数组。</p>
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<p>不知道你们发现没，这两个数组的关系跟 <code>&str</code> 与 <code>String</code> 的关系很像，前者是长度固定的字符串切片，后者是可动态增长的字符串。其实，在 Rust 中无论是 <code>String</code> 还是 <code>Vector</code>，它们都是 Rust 的高级类型：集合类型，在后面章节会有详细介绍。</p>
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<p>对于本章节，我们的重点还是放在数组 <code>array</code> 上。数组的具体定义很简单：将多个类型相同的元素依次组合在一起，就是一个数组。结合上面的内容，可以得出数组的三要素：</p>
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<ul>
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<li>长度固定</li>
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<li>元素必须有相同的类型</li>
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<li>依次线性排列</li>
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</ul>
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<p>这里再啰嗦一句，<strong>我们这里说的数组是 Rust 的基本类型，是固定长度的，这点与其他编程语言不同，其它编程语言的数组往往是可变长度的，与 Rust 中的动态数组 <code>Vector</code> 类似</strong>，希望读者大大牢记此点。</p>
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<h3 id="创建数组"><a class="header" href="#创建数组">创建数组</a></h3>
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<p>在 Rust 中，数组是这样定义的：</p>
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<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
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let a = [1, 2, 3, 4, 5];
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}</code></pre></pre>
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<p>数组语法跟 JavaScript 很像，也跟大多数编程语言很像。由于它的元素类型大小固定，且长度也是固定，因此<strong>数组 <code>array</code> 是存储在栈上</strong>，性能也会非常优秀。与此对应，<strong>动态数组 <code>Vector</code> 是存储在堆上</strong>，因此长度可以动态改变。当你不确定是使用数组还是动态数组时，那就应该使用后者，具体见<a href="https://course.rs/basic/collections/vector.html">动态数组 Vector</a>。</p>
|
|
|
|
|
|
<p>举个例子，在需要知道一年中各个月份名称的程序中，你很可能希望使用的是数组而不是动态数组。因为月份是固定的，它总是只包含 12 个元素：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>let months = ["January", "February", "March", "April", "May", "June", "July",
|
|
|
|
|
|
"August", "September", "October", "November", "December"];
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>在一些时候，还需要为<strong>数组声明类型</strong>，如下所示：</p>
|
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|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>let a: [i32; 5] = [1, 2, 3, 4, 5];
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>这里，数组类型是通过方括号语法声明，<code>i32</code> 是元素类型，分号后面的数字 <code>5</code> 是数组长度，数组类型也从侧面说明了<strong>数组的元素类型要统一，长度要固定</strong>。</p>
|
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|
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<p>还可以使用下面的语法初始化一个<strong>某个值重复出现 N 次的数组</strong>：</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() {
|
|
|
|
|
|
</span>let a = [3; 5];
|
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|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p><code>a</code> 数组包含 <code>5</code> 个元素，这些元素的初始化值为 <code>3</code>，聪明的读者已经发现，这种语法跟数组类型的声明语法其实是保持一致的：<code>[3; 5]</code> 和 <code>[类型; 长度]</code>。</p>
|
|
|
|
|
|
<p>在元素重复的场景，这种写法要简单的多，否则你就得疯狂敲击键盘：<code>let a = [3, 3, 3, 3, 3];</code>，不过老板可能很喜欢你的这种疯狂编程的状态。</p>
|
|
|
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|
|
<h3 id="访问数组元素"><a class="header" href="#访问数组元素">访问数组元素</a></h3>
|
|
|
|
|
|
<p>因为数组是连续存放元素的，因此可以通过索引的方式来访问存放其中的元素：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
|
|
|
|
|
|
let a = [9, 8, 7, 6, 5];
|
|
|
|
|
|
|
|
|
|
|
|
let first = a[0]; // 获取a数组第一个元素
|
|
|
|
|
|
let second = a[1]; // 获取第二个元素
|
|
|
|
|
|
}</code></pre></pre>
|
|
|
|
|
|
<p>与许多语言类似，数组的索引下标是从 0 开始的。此处，<code>first</code> 获取到的值是 <code>9</code>，<code>second</code> 是 <code>8</code>。</p>
|
|
|
|
|
|
<h4 id="越界访问"><a class="header" href="#越界访问">越界访问</a></h4>
|
|
|
|
|
|
<p>如果使用超出数组范围的索引访问数组元素，会怎么样？下面是一个接收用户的控制台输入，然后将其作为索引访问数组元素的例子：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::io;
|
|
|
|
|
|
|
|
|
|
|
|
fn main() {
|
|
|
|
|
|
let a = [1, 2, 3, 4, 5];
|
|
|
|
|
|
|
|
|
|
|
|
println!("Please enter an array index.");
|
|
|
|
|
|
|
|
|
|
|
|
let mut index = String::new();
|
|
|
|
|
|
// 读取控制台的输出
|
|
|
|
|
|
io::stdin()
|
|
|
|
|
|
.read_line(&mut index)
|
|
|
|
|
|
.expect("Failed to read line");
|
|
|
|
|
|
|
|
|
|
|
|
let index: usize = index
|
|
|
|
|
|
.trim()
|
|
|
|
|
|
.parse()
|
|
|
|
|
|
.expect("Index entered was not a number");
|
|
|
|
|
|
|
|
|
|
|
|
let element = a[index];
|
|
|
|
|
|
|
|
|
|
|
|
println!(
|
|
|
|
|
|
"The value of the element at index {} is: {}",
|
|
|
|
|
|
index, element
|
|
|
|
|
|
);
|
|
|
|
|
|
}</code></pre></pre>
|
|
|
|
|
|
<p>使用 <code>cargo run</code> 来运行代码，因为数组只有 5 个元素，如果我们试图输入 <code>5</code> 去访问第 6 个元素，则会访问到不存在的数组元素，最终程序会崩溃退出：</p>
|
|
|
|
|
|
<pre><code class="language-console">Please enter an array index.
|
|
|
|
|
|
5
|
|
|
|
|
|
thread 'main' panicked at 'index out of bounds: the len is 5 but the index is 5', src/main.rs:19:19
|
|
|
|
|
|
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>这就是数组访问越界，访问了数组中不存在的元素，导致 Rust 运行时错误。程序因此退出并显示错误消息，未执行最后的 <code>println!</code> 语句。</p>
|
|
|
|
|
|
<p>当你尝试使用索引访问元素时，Rust 将检查你指定的索引是否小于数组长度。如果索引大于或等于数组长度，Rust 会出现 <strong><em>panic</em></strong>。这种检查只能在运行时进行，比如在上面这种情况下，编译器无法在编译期知道用户运行代码时将输入什么值。</p>
|
|
|
|
|
|
<p>这种就是 Rust 的安全特性之一。在很多系统编程语言中，并不会检查数组越界问题，你会访问到无效的内存地址获取到一个风马牛不相及的值，最终导致在程序逻辑上出现大问题，而且这种问题会非常难以检查。</p>
|
|
|
|
|
|
<h4 id="数组元素为非基础类型"><a class="header" href="#数组元素为非基础类型">数组元素为非基础类型</a></h4>
|
|
|
|
|
|
<p>学习了上面的知识，很多朋友肯定觉得已经学会了Rust的数组类型，但现实会给我们一记重锤，实际开发中还会碰到一种情况，就是<strong>数组元素是非基本类型</strong>的，这时候大家一定会这样写。</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>let array = [String::from("rust is good!"); 8];
|
|
|
|
|
|
|
|
|
|
|
|
println!("{:#?}", array);
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>然后你会惊喜的得到编译错误。</p>
|
|
|
|
|
|
<pre><code class="language-console">error[E0277]: the trait bound `String: std::marker::Copy` is not satisfied
|
|
|
|
|
|
--> src/main.rs:7:18
|
|
|
|
|
|
|
|
|
|
|
|
|
7 | let array = [String::from("rust is good!"); 8];
|
|
|
|
|
|
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `String`
|
|
|
|
|
|
|
|
|
|
|
|
|
= note: the `Copy` trait is required because this value will be copied for each element of the array
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>有些还没有看过特征的小伙伴，有可能不太明白这个报错，不过这个目前可以不提，我们就拿之前所学的<a href="https://course.rs/basic/ownership/ownership.html">所有权</a>知识，就可以思考明白，前面几个例子都是Rust的基本类型，而<strong>基本类型在Rust中赋值是以Copy的形式</strong>，这时候你就懂了吧，<code>let array=[3;5]</code>底层就是不断的Copy出来的，但很可惜复杂类型都没有深拷贝，只能一个个创建。</p>
|
|
|
|
|
|
<p>接着就有小伙伴会这样写。</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>let array = [String::from("rust is good!"),String::from("rust is good!"),String::from("rust is good!")];
|
|
|
|
|
|
|
|
|
|
|
|
println!("{:#?}", array);
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>作为一个追求极致完美的Rust开发者，怎么能容忍上面这么难看的代码存在！</p>
|
|
|
|
|
|
<p><strong>正确的写法</strong>，应该调用<code>std::array::from_fn</code></p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>let array: [String; 8] = std::array::from_fn(|_i| String::from("rust is good!"));
|
|
|
|
|
|
|
|
|
|
|
|
println!("{:#?}", array);
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<h2 id="数组切片"><a class="header" href="#数组切片">数组切片</a></h2>
|
|
|
|
|
|
<p>在之前的<a href="https://course.rs/basic/compound-type/string-slice.html#%E5%88%87%E7%89%87slice">章节</a>，我们有讲到 <code>切片</code> 这个概念，它允许你引用集合中的部分连续片段，而不是整个集合，对于数组也是，数组切片允许我们引用数组的一部分：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>let a: [i32; 5] = [1, 2, 3, 4, 5];
|
|
|
|
|
|
|
|
|
|
|
|
let slice: &[i32] = &a[1..3];
|
|
|
|
|
|
|
|
|
|
|
|
assert_eq!(slice, &[2, 3]);
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>上面的数组切片 <code>slice</code> 的类型是<code>&[i32]</code>，与之对比，数组的类型是<code>[i32;5]</code>，简单总结下切片的特点：</p>
|
|
|
|
|
|
<ul>
|
|
|
|
|
|
<li>切片的长度可以与数组不同，并不是固定的，而是取决于你使用时指定的起始和结束位置</li>
|
|
|
|
|
|
<li>创建切片的代价非常小，因为切片只是针对底层数组的一个引用</li>
|
|
|
|
|
|
<li>切片类型[T]拥有不固定的大小，而切片引用类型&[T]则具有固定的大小，因为 Rust 很多时候都需要固定大小数据类型，因此&[T]更有用,<code>&str</code>字符串切片也同理</li>
|
|
|
|
|
|
</ul>
|
|
|
|
|
|
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
|
|
|
|
|
|
<p>最后，让我们以一个综合性使用数组的例子，来结束本章节的学习：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
|
|
|
|
|
|
// 编译器自动推导出one的类型
|
|
|
|
|
|
let one = [1, 2, 3];
|
|
|
|
|
|
// 显式类型标注
|
|
|
|
|
|
let two: [u8; 3] = [1, 2, 3];
|
|
|
|
|
|
let blank1 = [0; 3];
|
|
|
|
|
|
let blank2: [u8; 3] = [0; 3];
|
|
|
|
|
|
|
|
|
|
|
|
// arrays是一个二维数组，其中每一个元素都是一个数组，元素类型是[u8; 3]
|
|
|
|
|
|
let arrays: [[u8; 3]; 4] = [one, two, blank1, blank2];
|
|
|
|
|
|
|
|
|
|
|
|
// 借用arrays的元素用作循环中
|
|
|
|
|
|
for a in &arrays {
|
|
|
|
|
|
print!("{:?}: ", a);
|
|
|
|
|
|
// 将a变成一个迭代器，用于循环
|
|
|
|
|
|
// 你也可以直接用for n in a {}来进行循环
|
|
|
|
|
|
for n in a.iter() {
|
|
|
|
|
|
print!("\t{} + 10 = {}", n, n+10);
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
let mut sum = 0;
|
|
|
|
|
|
// 0..a.len,是一个 Rust 的语法糖，其实就等于一个数组，元素是从0,1,2一直增加到到a.len-1
|
|
|
|
|
|
for i in 0..a.len() {
|
|
|
|
|
|
sum += a[i];
|
|
|
|
|
|
}
|
|
|
|
|
|
println!("\t({:?} = {})", a, sum);
|
|
|
|
|
|
}
|
|
|
|
|
|
}</code></pre></pre>
|
|
|
|
|
|
<p>做个总结，数组虽然很简单，但是其实还是存在几个要注意的点：</p>
|
|
|
|
|
|
<ul>
|
|
|
|
|
|
<li><strong>数组类型容易跟数组切片混淆</strong>，[T;n]描述了一个数组的类型，而[T]描述了切片的类型， 因为切片是运行期的数据结构，它的长度无法在编译期得知，因此不能用[T;n]的形式去描述</li>
|
|
|
|
|
|
<li><code>[u8; 3]</code>和<code>[u8; 4]</code>是不同的类型，数组的长度也是类型的一部分</li>
|
|
|
|
|
|
<li><strong>在实际开发中，使用最多的是数组切片[T]</strong>，我们往往通过引用的方式去使用<code>&[T]</code>，因为后者有固定的类型大小</li>
|
|
|
|
|
|
</ul>
|
|
|
|
|
|
<p>至此，关于数据类型部分，我们已经全部学完了，对于 Rust 学习而言，我们也迈出了坚定的第一步，后面将开始更高级特性的学习。未来如果大家有疑惑需要检索知识，一样可以继续回顾过往的章节，因为本书不仅仅是一门 Rust 的教程，还是一本厚重的 Rust 工具书。</p>
|
|
|
|
|
|
<h2 id="课后练习"><a class="header" href="#课后练习">课后练习</a></h2>
|
|
|
|
|
|
<blockquote>
|
|
|
|
|
|
<p><a href="https://practice-zh.course.rs/compound-types/array.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/array.md">习题解答</a>。</p>
|
|
|
|
|
|
</blockquote>
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