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<main>
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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> && <code>IsTerminal</code></a></h1>
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<blockquote>
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<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>
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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 1.70 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="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>
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<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>
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<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>
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<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>
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<h2 id="oncecell-和-oncelock"><a class="header" href="#oncecell-和-oncelock"><code>OnceCell</code> 和 <code>OnceLock</code></a></h2>
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<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>
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<pre><pre class="playground"><code class="language-rust edition2021">use std::sync::OnceLock;
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static WINNER: OnceLock<&str> = OnceLock::new();
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fn main() {
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let winner = std::thread::scope(|s| {
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s.spawn(|| WINNER.set("thread"));
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std::thread::yield_now(); // give them a chance...
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WINNER.get_or_init(|| "main")
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});
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println!("{winner} wins!");
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}</code></pre></pre>
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<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> 的 <code>unsync</code> 和 <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> 和 <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>
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<h2 id="isterminal"><a class="header" href="#isterminal"><code>IsTerminal</code></a></h2>
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<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>
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<pre><pre class="playground"><code class="language-rust edition2021">use std::io::{stdout, IsTerminal};
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fn main() {
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let use_color = stdout().is_terminal();
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// if so, add color codes to program output...
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}</code></pre></pre>
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<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>
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<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>
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<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>
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<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>
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<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>
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<h2 id="others"><a class="header" href="#others">Others</a></h2>
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<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>
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<p>注：可以看到常用的 <code>Option</code> <code>Result</code> 新增了一些方法：</p>
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<ul>
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<li><code>Option::is_some_and</code>
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<ul>
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<li><code>pub fn is_some_and(self, f: impl FnOnce(T) -> bool) -> bool</code></li>
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</ul>
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</li>
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<li><code>Result::is_ok_and</code>
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<ul>
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<li><code>pub fn is_ok_and(self, f: impl FnOnce(T) -> bool) -> bool</code></li>
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</ul>
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</li>
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<li><code>Result::is_err_and</code>
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<ul>
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<li><code>pub fn is_err_and(self, f: impl FnOnce(E) -> bool) -> bool</code></li>
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</ul>
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</li>
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</ul>
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<p>平时使用时可以试试。</p>
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