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<main>
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<h1 id="rust-新版解读--165--重点-泛型关联类型新绑定语法"><a class="header" href="#rust-新版解读--165--重点-泛型关联类型新绑定语法">Rust 新版解读 | 1.65 | 重点: 泛型关联类型，新绑定语法！</a></h1>
|
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<blockquote>
|
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<p>Rust 1.65 官方 release doc: <a href="https://blog.rust-lang.org/2022/11/03/Rust-1.65.0.html">Announcing Rust 1.65.0 | Rust Blog</a></p>
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</blockquote>
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<p>通过 <a href="https://www.rust-lang.org/tools/install">rustup</a> 安装的同学可以使用以下命令升级到 1.65 版本:</p>
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<pre><code class="language-shell">$ rustup update stable
|
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</code></pre>
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<h2 id="泛型关联类型-generic-associated-types-gats"><a class="header" href="#泛型关联类型-generic-associated-types-gats">泛型关联类型 Generic associated types (GATs)</a></h2>
|
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<p>关联类型（associated types）里现在可以加上生命周期、类型、const泛型了，类似于：</p>
|
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|
<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>trait Foo {
|
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|
type Bar<'x>;
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}
|
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<span class="boring">}</span></code></pre>
|
|
|
<p>三言两语说不清这个变化的好处，看几个例子来感受一下：</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>/// 一个类似于 `Iterator` 的 trait ，可以借用 `Self`。
|
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|
trait LendingIterator {
|
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|
type Item<'a> where Self: 'a;
|
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|
fn next<'a>(&'a mut self) -> Option<Self::Item<'a>>;
|
|
|
}
|
|
|
|
|
|
/// 可以给智能指针类型，比如 `Rc` 和 `Arc` 实现的 trait，来实现指针类型的泛用性
|
|
|
trait PointerFamily {
|
|
|
type Pointer<T>: Deref<Target = T>;
|
|
|
|
|
|
fn new<T>(value: T) -> Self::Pointer<T>;
|
|
|
}
|
|
|
|
|
|
/// 允许借用数组对象，对不需要连续存储数据的固定长度数组类型很有用
|
|
|
trait BorrowArray<T> {
|
|
|
type Array<'x, const N: usize> where Self: 'x;
|
|
|
|
|
|
fn borrow_array<'a, const N: usize>(&'a self) -> Self::Array<'a, N>;
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p>泛型关联类型十分通用，能够写出许多之前无法实现的模式。更多的信息可以参考下面的链接：</p>
|
|
|
<ul>
|
|
|
<li><a href="https://blog.rust-lang.org/2021/08/03/GATs-stabilization-push.html">2021/08/03/GAT稳定版本推进</a></li>
|
|
|
<li><a href="https://blog.rust-lang.org/2022/10/28/gats-stabilization.html">2022/10/28/GAT稳定版本发布公告</a></li>
|
|
|
</ul>
|
|
|
<p>第一个对上面的例子进行了更深入的讨论，第二个讨论了一些已知的局限性。</p>
|
|
|
<p>更深入的阅读可以在关联类型的 <a href="https://doc.rust-lang.org/nightly/reference/items/associated-items.html#associated-types">nightly reference</a> 和 <a href="https://rust-lang.github.io/rfcs/1598-generic_associated_types.html">原始 RFC</a>（已经过去6.5年了！） 里找到。</p>
|
|
|
<h2 id="let---else-语法"><a class="header" href="#let---else-语法"><code>let</code> - <code>else</code> 语法</a></h2>
|
|
|
<p>新的 <code>let</code> 语法，尝试模式匹配，找不到匹配的情况下执行发散的 <code>else</code> 块。</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>let PATTERN: TYPE = EXPRESSION else {
|
|
|
DIVERGING_CODE;
|
|
|
};
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p>常规的 <code>let</code> 语法仅能使用 <code>irrefutable patterns</code>，直译为不可反驳的模式，也就是一定要匹配上。一般情况下都是单个变量绑定，也用在解开结构体，元组，数组等复合类型上。原先并不适用条件匹配，比如从枚举里确定枚举值。直到现在我们有了 <code>let</code> - <code>else</code>。这是 <code>refutable pattern</code>，直译为可反驳的模式，能够像常规 <code>let</code> 一样匹配并绑定变量到周围范围内，在模式不匹配的时候执行发送的 <code>else</code> （可以是 <code>break</code>, <code>return</code>, <code>panic!</code>）。</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>fn get_count_item(s: &str) -> (u64, &str) {
|
|
|
let mut it = s.split(' ');
|
|
|
let (Some(count_str), Some(item)) = (it.next(), it.next()) else {
|
|
|
panic!("Can't segment count item pair: '{s}'");
|
|
|
};
|
|
|
let Ok(count) = u64::from_str(count_str) else {
|
|
|
panic!("Can't parse integer: '{count_str}'");
|
|
|
};
|
|
|
(count, item)
|
|
|
}
|
|
|
assert_eq!(get_count_item("3 chairs"), (3, "chairs"));
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p><code>if</code> - <code>else</code> 和 <code>match</code> 或者 <code>if let</code> 最大不一样的地方是变量绑定的范围，在此之前你需要多写一点重复的代码和一次外层的 <code>let</code> 绑定来完成：</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span> let (count_str, item) = match (it.next(), it.next()) {
|
|
|
(Some(count_str), Some(item)) => (count_str, item),
|
|
|
_ => panic!("Can't segment count item pair: '{s}'"),
|
|
|
};
|
|
|
let count = if let Ok(count) = u64::from_str(count_str) {
|
|
|
count
|
|
|
} else {
|
|
|
panic!("Can't parse integer: '{count_str}'");
|
|
|
};
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<h2 id="break-跳出标记过的代码块"><a class="header" href="#break-跳出标记过的代码块"><code>break</code> 跳出标记过的代码块</a></h2>
|
|
|
<p>块表达式现在可以标记为 <code>break</code> 的目标，来达到提前终止块的目的。这听起来有点像 <code>goto</code> 语法，不过这并不是随意的跳转，只能从块里跳转到块末尾。这在之前已经可以用 <code>loop</code> 块来实现了，你可能大概率见过这种总是只执行一次的 <code>loop</code>。</p>
|
|
|
<p>1.65 可以直接给块语句添加标记来提前退出了，还可以携带返回值：</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>let result = 'block: {
|
|
|
do_thing();
|
|
|
if condition_not_met() {
|
|
|
break 'block 1;
|
|
|
}
|
|
|
do_next_thing();
|
|
|
if condition_not_met() {
|
|
|
break 'block 2;
|
|
|
}
|
|
|
do_last_thing();
|
|
|
3
|
|
|
};
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<h2 id="others"><a class="header" href="#others">Others</a></h2>
|
|
|
<p>其它更新细节，和稳定的API列表，参考<a href="https://blog.rust-lang.org/2022/11/03/Rust-1.65.0.html">原Blog</a></p>
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