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<h1 id="rust-新版解读--188--let_chains"><a class="header" href="#rust-新版解读--188--let_chains">Rust 新版解读 | 1.88 | let_chains</a></h1>
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<blockquote>
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<p>Rust 1.88 官方 release doc: <a href="https://blog.rust-lang.org/2025/06/26/Rust-1.88.0/">Announcing Rust 1.88.0 | 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 1.88 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="let-链式表达式"><a class="header" href="#let-链式表达式">let 链式表达式</a></h2>
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<p>该特性允许在 <code>if</code> 和 <code>while</code> 条件中使用 <code>&&</code> 连接的 <code>let</code> 语句，甚至可以与布尔表达式混合使用，从而减少 <code>if</code>/<code>if let</code> 和 <code>while</code>/<code>while let</code> 之间的差异。<code>let</code> 子表达式中的模式可以是不可反驳或可反驳的，绑定变量可以在链式后续部分和代码体中使用。</p>
|
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<p>例如，以下代码片段组合了多个条件，之前需要嵌套 <code>if let</code> 和 <code>if</code> 块才能实现：</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>if let Channel::Stable(v) = release_info()
|
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&& let Semver { major, minor, .. } = v
|
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&& major == 1
|
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&& minor == 88
|
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{
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println!("`let_chains` 在此版本中已稳定");
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}
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<span class="boring">}</span></code></pre>
|
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|
<p>由于一些边界场景难以兼容，let 链式表达式仅在 Rust 2024 版本中可用，因为该特性依赖于 <a href="https://doc.rust-lang.org/edition-guide/rust-2024/temporary-if-let-scope.html"><code>if let</code> 临时作用域</a> 变更以实现更一致的析构顺序。</p>
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<h2 id="裸函数"><a class="header" href="#裸函数">裸函数</a></h2>
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<p>Rust 现在支持编写没有编译器生成的收尾代码和序言的裸函数，允许完全控制特定函数的生成汇编代码。这是在 <code>global_asm!</code> 块中定义函数的更符合人体工程学的替代方案。裸函数使用 <code>#[unsafe(naked)]</code> 属性标记，其函数体由单个 <code>naked_asm!</code> 调用组成。</p>
|
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<p>例如：</p>
|
|
|
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>#[unsafe(naked)]
|
|
|
pub unsafe extern "sysv64" fn wrapping_add(a: u64, b: u64) -> u64 {
|
|
|
// 等同于 `a.wrapping_add(b)`。
|
|
|
core::arch::naked_asm!(
|
|
|
"lea rax, [rdi + rsi]",
|
|
|
"ret"
|
|
|
);
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre>
|
|
|
<p>手写的汇编块定义了整个函数体：与非裸函数不同，编译器不会对参数或返回值添加任何特殊处理。裸函数用于 Rust 的 <a href="https://github.com/rust-lang/compiler-builtins">compiler-builtins</a>、操作系统和嵌入式应用程序等场景。</p>
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<h2 id="布尔配置"><a class="header" href="#布尔配置">布尔配置</a></h2>
|
|
|
<p><code>cfg</code> 谓词现在支持布尔字面量 <code>true</code> 和 <code>false</code>，分别作为始终启用或禁用的配置。这适用于 Rust 的<a href="https://doc.rust-lang.org/reference/conditional-compilation.html">条件编译</a>中的 <code>cfg</code> 和 <code>cfg_attr</code> 属性以及内置的 <code>cfg!</code> 宏，也适用于 Cargo <code>[target]</code> 表中的<a href="https://doc.rust-lang.org/cargo/reference/config.html#target">配置</a>和<a href="https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#platform-specific-dependencies">清单</a>。</p>
|
|
|
<p>此前，空谓词列表可以用于无条件配置，例如 <code>cfg(all())</code> 用于启用，<code>cfg(any())</code> 用于禁用，但这种含义相当隐式且容易搞反。<code>cfg(true)</code> 和 <code>cfg(false)</code> 提供了一种更直接的方式来表达你的意图。</p>
|
|
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<p>具体背景细节可以参考 <a href="https://rust-lang.github.io/rfcs/3695-cfg-boolean-literals.html">RFC-3695</a></p>
|
|
|
<h2 id="cargo-自动缓存清理"><a class="header" href="#cargo-自动缓存清理">Cargo 自动缓存清理</a></h2>
|
|
|
<p>从 1.88.0 开始，Cargo 将自动对其主目录中的缓存运行垃圾回收！</p>
|
|
|
<p>构建时，Cargo 会下载并缓存所需的依赖项。历史上，这些下载的文件永远不会被清理，导致 Cargo 主目录中的磁盘使用量无限增长。在此版本中，Cargo 引入了垃圾回收机制来自动清理旧文件（例如 <code>.crate</code> 文件）。Cargo 将删除从网络下载且 3 个月内未访问的文件，以及从本地系统获取且 1 个月内未访问的文件。请注意，如果在离线状态下运行（使用 <code>--offline</code> 或 <code>--frozen</code>），则不会进行此自动垃圾回收。</p>
|
|
|
<p>Cargo 1.78 以后会跟踪所需的访问信息以进行此垃圾回收。这是在实际清理开始之前引入的，以减少仍使用早期版本的用户的缓存更换。如果你经常使用比 1.78 版本更早的 Cargo 版本，并且希望某些仅由旧版本访问的 crate 不被重新下载，你可以在 Cargo 配置中设置 <code>cache.auto-clean-frequency = "never"</code>，如<a href="https://doc.rust-lang.org/nightly/cargo/reference/config.html#cache">文档</a>所述。</p>
|
|
|
<p>有关更多信息，请参阅此功能的原始<a href="https://blog.rust-lang.org/2023/12/11/cargo-cache-cleaning/">不稳定公告</a>。该设计的某些部分仍不稳定，例如 <a href="https://github.com/rust-lang/cargo/issues/13060">cargo#13060</a> 中跟踪的 <code>gc</code> 子命令，因此仍有更多值得期待的内容！</p>
|
|
|
<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/2025/06/26/Rust-1.88.0/#stabilized-apis">原Blog</a></p>
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