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<h1 id="rust-新版解读--162--重点-cargo-adddefault-枚举变量linux-上更薄更快的-mutex裸机-x86_64-构架"><a class="header" href="#rust-新版解读--162--重点-cargo-adddefault-枚举变量linux-上更薄更快的-mutex裸机-x86_64-构架">Rust 新版解读 | 1.62 | 重点: Cargo add#[default] 枚举变量Linux 上更薄更快的 Mutex裸机 x86_64 构架</a></h1>
<blockquote>
<p>原文链接: https://blog.rust-lang.org/2022/06/30/Rust-1.62.0.html
翻译 by <a href="https://github.com/AllanDowney">AllanDowney</a></p>
</blockquote>
<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 1.62 版本:</p>
<pre><code class="language-shell">$ rustup update stable
</code></pre>
<h2 id="cargo-add"><a class="header" href="#cargo-add">Cargo add</a></h2>
<p>现在可以使用 <code>cargo add</code> 直接从命令行添加新的依赖项。此命令支持指定功能和版本。它还可以用来修改现有的依赖关系。</p>
<p>例如:</p>
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>$ cargo add log
$ cargo add serde --features derive
$ cargo add nom@5
<span class="boring">}</span></code></pre>
<p>有关更多信息,请参阅 <a href="https://doc.rust-lang.org/nightly/cargo/commands/cargo-add.html">cargo 文档</a></p>
<h2 id="default-枚举变量"><a class="header" href="#default-枚举变量"><code>#[default]</code> 枚举变量</a></h2>
<p>如果指定枚举默认变量,现在可以使用 <code>#[derive(Default)]</code>。例如,到目前为止,您必须手动为此枚举写入 <code>Default</code> </p>
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>#[derive(Default)]
enum Maybe&lt;T&gt; {
#[default]
Nothing,
Something(T),
}
<span class="boring">}</span></code></pre>
<p>到目前为止,只允许将“单元”变量(没有字段的变量)标记为#[default]。<a href="https://rust-lang.github.io/rfcs/3107-derive-default-enum.html">RFC</a> 中提供了有关此功能的更多信息。</p>
<h2 id="linux-上更薄更快的-mutex"><a class="header" href="#linux-上更薄更快的-mutex">Linux 上更薄更快的 Mutex</a></h2>
<p>以前Linux 上的 <code>pthreads</code> 库支持 <code>Mutex</code><code>Condvar</code><code>RwLock</code><code>pthreads 锁</code> 支持比 Rust API 本身更多的功能,包括运行时配置,并且设计用于比 Rust 提供的静态保证更少的语言中。</p>
<p>例如,<code>Mutex</code> 实现是 40 个字节,不能被移动(move)。这迫使标准库在后台为使用 <code>pthreads</code> 的平台的每个新 <code>Mutex</code> 分配一个 <code>Box</code></p>
<p>现在 Rust 的标准库在 Linux 上提供了这些锁的原始 futex 实现,它非常轻量级,不需要额外分配。在 1.62.0 中,<code>Mutex</code> 在 Linux 上的内部状态只需要 5 个字节,尽管在未来的版本中可能会发生变化。</p>
<p>这是提高 Rust 的锁类型效率的长期努力的一部分,包括以前在 Windows 上的改进,如取消绑定其原语。您可以在<a href="https://github.com/rust-lang/rust/issues/93740">跟踪问题</a>中了解更多有关这方面的信息。</p>
<h2 id="裸机-x86_64-构架"><a class="header" href="#裸机-x86_64-构架">裸机 <code>x86_64</code> 构架</a></h2>
<p>现在更容易为 <code>x86_64</code> 构建无操作系统的二进制文件,例如在编写内核时。<code>x86_64-unknown-none</code> 构架已升级到第 2 层,可以用 <code>rustup</code> 安装。</p>
<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>$ rustup target add x86_64-unknown-none
$ rustc --target x86_64-unknown-none my_no_std_program.rs
<span class="boring">}</span></code></pre>
<p>您可以在 <a href="https://docs.rust-embedded.org/book/intro/no-std.html">Embedded Rust book</a> 中阅读更多关于使用 <code>no_std</code> 进行开发的信息。</p>
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