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<h1 id="rust-新版解读--170--oncecell--isterminal"><a class="header" href="#rust-新版解读--170--oncecell--isterminal">Rust 新版解读 | 1.70 | <code>OnceCell</code> &amp;&amp; <code>IsTerminal</code></a></h1>
<blockquote>
<p>Rust 1.70 官方 release doc: <a href="https://blog.rust-lang.org/2023/06/01/Rust-1.70.0.html">Announcing Rust 1.70.0 | Rust Blog</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 1.70 版本:</p>
<pre><code class="language-shell">$ rustup update stable
</code></pre>
<h2 id="cratesio-默认使用稀疏注册协议-sparse-protocol"><a class="header" href="#cratesio-默认使用稀疏注册协议-sparse-protocol">crates.io 默认使用稀疏注册协议 sparse protocol</a></h2>
<p>在 Rust 1.68.0 版本里稳定但需要手动配置来启用的特性,在这个版本中作为默认值了。如今在拉取 crates.io 索引信息时,应该能够观察到大幅性能提升。</p>
<p>注意当用户处在有防火墙限制的网络环境下时,需要确保能够访问 <code>https://index.crates.io</code> 来使用该协议。如果因为某些原因需要继续使用原先由 Github 托管的 git 索引,可以配置 <code>registries.crates-io.protocol</code> 来实现。</p>
<p>需要注意,两种访问方式依赖的本地缓存路径是不同的,所以更换访问方式会导致依赖被重新下载。当完全切换到稀疏注册协议后,或许你想要清理存储在 <code>$CARGO_HOME/registry/*/github.com-*</code> 的旧依赖项</p>
<h2 id="oncecell-和-oncelock"><a class="header" href="#oncecell-和-oncelock"><code>OnceCell</code><code>OnceLock</code></a></h2>
<p>稳定了 <code>OnceCell</code> 和多线程安全版本 <code>OnceLock</code> 两种共享数据类型,它们都能让数据不需要立刻初始化的同时保证仅初始化一次。</p>
<pre class="playground"><code class="language-rust edition2021">use std::sync::OnceLock;
static WINNER: OnceLock&lt;&amp;str&gt; = OnceLock::new();
fn main() {
let winner = std::thread::scope(|s| {
s.spawn(|| WINNER.set("thread"));
std::thread::yield_now(); // give them a chance...
WINNER.get_or_init(|| "main")
});
println!("{winner} wins!");
}</code></pre>
<p>在之前需要使用 <code>lazy_static</code> 或者 <code>once_cell</code> 来实现这种效果,如今标准库里从 <code>once_cell</code><code>unsync</code><code>sync</code> 模块吸收了这些基础组件。未来可能还会有更多方法被稳定下来,比如存储初始化函数的 <code>LazyCell</code><code>LazyLock</code> 类型。不过当前这第一步应该能够覆盖许多使用场景了。</p>
<h2 id="isterminal"><a class="header" href="#isterminal"><code>IsTerminal</code></a></h2>
<p>新稳定的 Trait包含 <code>is_terminal</code> 一个方法,判断给定的文件描述符或者句柄是否代表一个终端/TTY。标准化了之前第三方crates如 <code>atty</code> <code>is-terminal</code> 实现的功能。一个常见的使用场景是判断程序是通过脚本执行的还是交互模式执行的以此在交互模式下实现一些诸如彩色输出、完整TUI的功能。</p>
<pre class="playground"><code class="language-rust edition2021">use std::io::{stdout, IsTerminal};
fn main() {
let use_color = stdout().is_terminal();
// if so, add color codes to program output...
}</code></pre>
<h2 id="调试信息级别的文本化"><a class="header" href="#调试信息级别的文本化">调试信息级别的文本化</a></h2>
<p>之前 <code>-Cdebuginfo</code> 编译选项仅支持数字 0,1,2 来表示逐渐增多的 debug 调试信息。Cargo 默认在dev和test配置里是 2在release和bench配置里是 0</p>
<p>如今这些级别可以被文本代表“none” (0), “limited” (1), and “full” (2), 还有两个新级别“line-directives-only” and “line-tables-only”</p>
<p>之前 Cargo 和 rustc 的文档都把级别 1 叫做 “line-tables-only”但是级别 1 实际上比这种场景包含的调试信息更多。新的 “line-tables-only” 仅保留的文件名和行号信息的最少调试信息量,或许会在未来成为 <code>-Cdebuginfo=1</code> 。另外一个 “line-directives-only” 是为 NVPTX 场景准备的,不推荐使用。</p>
<p>注意这些文本化的选项还无法在 <code>Cargo.toml</code> 里使用,预计会在下一个 1.71版本里实现。</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/2023/06/01/Rust-1.70.0.html#stabilized-apis">原Blog</a></p>
<p>注:可以看到常用的 <code>Option</code> <code>Result</code> 新增了一些方法:</p>
<ul>
<li><code>Option::is_some_and</code>
<ul>
<li><code>pub fn is_some_and(self, f: impl FnOnce(T) -&gt; bool) -&gt; bool</code></li>
</ul>
</li>
<li><code>Result::is_ok_and</code>
<ul>
<li><code>pub fn is_ok_and(self, f: impl FnOnce(T) -&gt; bool) -&gt; bool</code></li>
</ul>
</li>
<li><code>Result::is_err_and</code>
<ul>
<li><code>pub fn is_err_and(self, f: impl FnOnce(E) -&gt; bool) -&gt; bool</code></li>
</ul>
</li>
</ul>
<p>平时使用时可以试试。</p>
</main>
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