|
|
<!DOCTYPE HTML>
|
|
|
<html lang="zh-CN" class="light" dir="ltr">
|
|
|
<head>
|
|
|
<!-- Book generated using mdBook -->
|
|
|
<meta charset="UTF-8">
|
|
|
<title>返回值 Result 和? - Rust语言圣经(Rust Course)</title>
|
|
|
|
|
|
|
|
|
<!-- Custom HTML head -->
|
|
|
|
|
|
<meta name="description" content="">
|
|
|
<meta name="viewport" content="width=device-width, initial-scale=1">
|
|
|
<meta name="theme-color" content="#ffffff">
|
|
|
|
|
|
<link rel="icon" href="../../favicon.svg">
|
|
|
<link rel="shortcut icon" href="../../favicon.png">
|
|
|
<link rel="stylesheet" href="../../css/variables.css">
|
|
|
<link rel="stylesheet" href="../../css/general.css">
|
|
|
<link rel="stylesheet" href="../../css/chrome.css">
|
|
|
<link rel="stylesheet" href="../../css/print.css" media="print">
|
|
|
|
|
|
<!-- Fonts -->
|
|
|
<link rel="stylesheet" href="../../FontAwesome/css/font-awesome.css">
|
|
|
<link rel="stylesheet" href="../../fonts/fonts.css">
|
|
|
|
|
|
<!-- Highlight.js Stylesheets -->
|
|
|
<link rel="stylesheet" href="../../highlight.css">
|
|
|
<link rel="stylesheet" href="../../tomorrow-night.css">
|
|
|
<link rel="stylesheet" href="../../ayu-highlight.css">
|
|
|
|
|
|
<!-- Custom theme stylesheets -->
|
|
|
<link rel="stylesheet" href="../../theme/style.css">
|
|
|
|
|
|
</head>
|
|
|
<body class="sidebar-visible no-js">
|
|
|
<div id="body-container">
|
|
|
<!-- Provide site root to javascript -->
|
|
|
<script>
|
|
|
var path_to_root = "../../";
|
|
|
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
|
|
</script>
|
|
|
|
|
|
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
|
|
<script>
|
|
|
try {
|
|
|
var theme = localStorage.getItem('mdbook-theme');
|
|
|
var sidebar = localStorage.getItem('mdbook-sidebar');
|
|
|
|
|
|
if (theme.startsWith('"') && theme.endsWith('"')) {
|
|
|
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
|
|
|
}
|
|
|
|
|
|
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
|
|
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
|
|
}
|
|
|
} catch (e) { }
|
|
|
</script>
|
|
|
|
|
|
<!-- Set the theme before any content is loaded, prevents flash -->
|
|
|
<script>
|
|
|
var theme;
|
|
|
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
|
|
if (theme === null || theme === undefined) { theme = default_theme; }
|
|
|
var html = document.querySelector('html');
|
|
|
html.classList.remove('light')
|
|
|
html.classList.add(theme);
|
|
|
var body = document.querySelector('body');
|
|
|
body.classList.remove('no-js')
|
|
|
body.classList.add('js');
|
|
|
</script>
|
|
|
|
|
|
<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
|
|
|
|
|
|
<!-- Hide / unhide sidebar before it is displayed -->
|
|
|
<script>
|
|
|
var body = document.querySelector('body');
|
|
|
var sidebar = null;
|
|
|
var sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
|
|
|
if (document.body.clientWidth >= 1080) {
|
|
|
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
|
|
sidebar = sidebar || 'visible';
|
|
|
} else {
|
|
|
sidebar = 'hidden';
|
|
|
}
|
|
|
sidebar_toggle.checked = sidebar === 'visible';
|
|
|
body.classList.remove('sidebar-visible');
|
|
|
body.classList.add("sidebar-" + sidebar);
|
|
|
</script>
|
|
|
|
|
|
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
|
|
|
<div class="sidebar-scrollbox">
|
|
|
<ol class="chapter"><li class="chapter-item affix "><a href="../../about-book.html">关于本书</a></li><li class="chapter-item affix "><a href="../../into-rust.html">进入 Rust 编程世界</a></li><li class="chapter-item affix "><a href="../../first-try/sth-you-should-not-do.html">避免从入门到放弃</a></li><li class="chapter-item affix "><a href="../../community.html">社区和锈书</a></li><li class="spacer"></li><li class="chapter-item affix "><a href="../../some-thoughts.html">Xobserve: 一切皆可观测</a></li><li class="chapter-item affix "><a href="../../beat-ai.html">BeatAI: 工程师 AI 入门圣经</a></li><li class="chapter-item affix "><li class="part-title">Rust 语言基础学习</li><li class="spacer"></li><li class="chapter-item "><a href="../../first-try/intro.html"><strong aria-hidden="true">1.</strong> 寻找牛刀，以便小试</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../first-try/installation.html"><strong aria-hidden="true">1.1.</strong> 安装 Rust 环境</a></li><li class="chapter-item "><a href="../../first-try/editor.html"><strong aria-hidden="true">1.2.</strong> 墙推 VSCode!</a></li><li class="chapter-item "><a href="../../first-try/cargo.html"><strong aria-hidden="true">1.3.</strong> 认识 Cargo</a></li><li class="chapter-item "><a href="../../first-try/hello-world.html"><strong aria-hidden="true">1.4.</strong> 不仅仅是 Hello world</a></li><li class="chapter-item "><a href="../../first-try/slowly-downloading.html"><strong aria-hidden="true">1.5.</strong> 下载依赖太慢了？</a></li></ol></li><li class="chapter-item expanded "><a href="../../basic/intro.html"><strong aria-hidden="true">2.</strong> Rust 基础入门</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/variable.html"><strong aria-hidden="true">2.1.</strong> 变量绑定与解构</a></li><li class="chapter-item "><a href="../../basic/base-type/index.html"><strong aria-hidden="true">2.2.</strong> 基本类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/base-type/numbers.html"><strong aria-hidden="true">2.2.1.</strong> 数值类型</a></li><li class="chapter-item "><a href="../../basic/base-type/char-bool.html"><strong aria-hidden="true">2.2.2.</strong> 字符、布尔、单元类型</a></li><li class="chapter-item "><a href="../../basic/base-type/statement-expression.html"><strong aria-hidden="true">2.2.3.</strong> 语句与表达式</a></li><li class="chapter-item "><a href="../../basic/base-type/function.html"><strong aria-hidden="true">2.2.4.</strong> 函数</a></li></ol></li><li class="chapter-item "><a href="../../basic/ownership/index.html"><strong aria-hidden="true">2.3.</strong> 所有权和借用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/ownership/ownership.html"><strong aria-hidden="true">2.3.1.</strong> 所有权</a></li><li class="chapter-item "><a href="../../basic/ownership/borrowing.html"><strong aria-hidden="true">2.3.2.</strong> 引用与借用</a></li></ol></li><li class="chapter-item "><a href="../../basic/compound-type/intro.html"><strong aria-hidden="true">2.4.</strong> 复合类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/compound-type/string-slice.html"><strong aria-hidden="true">2.4.1.</strong> 字符串与切片</a></li><li class="chapter-item "><a href="../../basic/compound-type/tuple.html"><strong aria-hidden="true">2.4.2.</strong> 元组</a></li><li class="chapter-item "><a href="../../basic/compound-type/struct.html"><strong aria-hidden="true">2.4.3.</strong> 结构体</a></li><li class="chapter-item "><a href="../../basic/compound-type/enum.html"><strong aria-hidden="true">2.4.4.</strong> 枚举</a></li><li class="chapter-item "><a href="../../basic/compound-type/array.html"><strong aria-hidden="true">2.4.5.</strong> 数组</a></li></ol></li><li class="chapter-item "><a href="../../basic/flow-control.html"><strong aria-hidden="true">2.5.</strong> 流程控制</a></li><li class="chapter-item "><a href="../../basic/match-pattern/intro.html"><strong aria-hidden="true">2.6.</strong> 模式匹配</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/match-pattern/match-if-let.html"><strong aria-hidden="true">2.6.1.</strong> match 和 if let</a></li><li class="chapter-item "><a href="../../basic/match-pattern/option.html"><strong aria-hidden="true">2.6.2.</strong> 解构 Option</a></li><li class="chapter-item "><a href="../../basic/match-pattern/pattern-match.html"><strong aria-hidden="true">2.6.3.</strong> 模式适用场景</a></li><li class="chapter-item "><a href="../../basic/match-pattern/all-patterns.html"><strong aria-hidden="true">2.6.4.</strong> 全模式列表</a></li></ol></li><li class="chapter-item "><a href="../../basic/method.html"><strong aria-hidden="true">2.7.</strong> 方法 Method</a></li><li class="chapter-item "><a href="../../basic/trait/intro.html"><strong aria-hidden="true">2.8.</strong> 泛型和特征</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/trait/generic.html"><strong aria-hidden="true">2.8.1.</strong> 泛型 Generics</a></li><li class="chapter-item "><a href="../../basic/trait/trait.html"><strong aria-hidden="true">2.8.2.</strong> 特征 Trait</a></li><li class="chapter-item "><a href="../../basic/trait/trait-object.html"><strong aria-hidden="true">2.8.3.</strong> 特征对象</a></li><li class="chapter-item "><a href="../../basic/trait/advance-trait.html"><strong aria-hidden="true">2.8.4.</strong> 进一步深入特征</a></li></ol></li><li class="chapter-item "><a href="../../basic/collections/intro.html"><strong aria-hidden="true">2.9.</strong> 集合类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/collections/vector.html"><strong aria-hidden="true">2.9.1.</strong> 动态数组 Vector</a></li><li class="chapter-item "><a href="../../basic/collections/hashmap.html"><strong aria-hidden="true">2.9.2.</strong> KV 存储 HashMap</a></li></ol></li><li class="chapter-item "><a href="../../basic/lifetime.html"><strong aria-hidden="true">2.10.</strong> 认识生命周期</a></li><li class="chapter-item expanded "><a href="../../basic/result-error/intro.html"><strong aria-hidden="true">2.11.</strong> 返回值和错误处理</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/result-error/panic.html"><strong aria-hidden="true">2.11.1.</strong> panic! 深入剖析</a></li><li class="chapter-item expanded "><a href="../../basic/result-error/result.html" class="active"><strong aria-hidden="true">2.11.2.</strong> 返回值 Result 和?</a></li></ol></li><li class="chapter-item "><a href="../../basic/crate-module/intro.html"><strong aria-hidden="true">2.12.</strong> 包和模块</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/crate-module/crate.html"><strong aria-hidden="true">2.12.1.</strong> 包 Crate</a></li><li class="chapter-item "><a href="../../basic/crate-module/module.html"><strong aria-hidden="true">2.12.2.</strong> 模块 Module</a></li><li class="chapter-item "><a href="../../basic/crate-module/use.html"><strong aria-hidden="true">2.12.3.</strong> 使用 use 引入模块及受限可见性</a></li></ol></li><li class="chapter-item "><a href="../../basic/comment.html"><strong aria-hidden="true">2.13.</strong> 注释和文档</a></li><li class="chapter-item "><a href="../../basic/formatted-output.html"><strong aria-hidden="true">2.14.</strong> 格式化输出</a></li></ol></li><li class="chapter-item "><a href="../../basic-practice/intro.html"><strong aria-hidden="true">3.</strong> 入门实战：文件搜索工具</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic-practice/base-features.html"><strong aria-hidden="true">3.1.</strong> 基本功能</a></li><li class="chapter-item "><a href="../../basic-practice/refactoring.html"><strong aria-hidden="true">3.2.</strong> 增加模块化和错误处理</a></li><li class="chapter-item "><a href="../../basic-practice/tests.html"><strong aria-hidden="true">3.3.</strong> 测试驱动开发</a></li><li class="chapter-item "><a href="../../basic-practice/envs.html"><strong aria-hidden="true">3.4.</strong> 使用环境变量</a></li><li class="chapter-item "><a href="../../basic-practice/stderr.html"><strong aria-hidden="true">3.5.</strong> 重定向错误信息的输出</a></li><li class="chapter-item "><a href="../../basic-practice/iterators.html"><strong aria-hidden="true">3.6.</strong> 使用迭代器来改进程序(可选)</a></li></ol></li><li class="chapter-item "><li class="part-title">Rust 语言进阶学习</li><li class="spacer"></li><li class="chapter-item "><a href="../../advance/intro.html"><strong aria-hidden="true">4.</strong> Rust 高级进阶</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/lifetime/intro.html"><strong aria-hidden="true">4.1.</strong> 生命周期</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/lifetime/advance.html"><strong aria-hidden="true">4.1.1.</strong> 深入生命周期</a></li><li class="chapter-item "><a href="../../advance/lifetime/static.html"><strong aria-hidden="true">4.1.2.</strong> &'static 和 T: 'static</a></li></ol></li><li class="chapter-item "><a href="../../advance/functional-programing/intro.html"><strong aria-hidden="true">4.2.</strong> 函数式编程: 闭包、迭代器</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/functional-programing/closure.html"><strong aria-hidden="true">4.2.1.</strong> 闭包 Closure</a></li><li class="chapter-item "><a href="../../advance/functional-programing/iterator.html"><strong aria-hidden="true">4.2.2.</strong> 迭代器 Iterator</a></li></ol></li><li class="chapter-item "><a href="../../advance/into-types/intro.html"><strong aria-hidden="true">4.3.</strong> 深入类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/into-types/converse.html"><strong aria-hidden="true">4.3.1.</strong> 类型转换</a></li><li class="chapter-item "><a href="../../advance/into-types/custom-type.html"><strong aria-hidden="true">4.3.2.</strong> newtype 和 类型别名</a></li><li class="chapter-item "><a href="../../advance/into-types/sized.html"><strong aria-hidden="true">4.3.3.</strong> Sized 和不定长类型 DST</a></li><li class="chapter-item "><a href="../../advance/into-types/enum-int.html"><strong aria-hidden="true">4.3.4.</strong> 枚举和整数</a></li></ol></li><li class="chapter-item "><a href="../../advance/smart-pointer/intro.html"><strong aria-hidden="true">4.4.</strong> 智能指针</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/smart-pointer/box.html"><strong aria-hidden="true">4.4.1.</strong> Box堆对象分配</a></li><li class="chapter-item "><a href="../../advance/smart-pointer/deref.html"><strong aria-hidden="true">4.4.2.</strong> Deref 解引用</a></li><li class="chapter-item "><a href="../../advance/smart-pointer/drop.html"><strong aria-hidden="true">4.4.3.</strong> Drop 释放资源</a></li><li class="chapter-item "><a href="../../advance/smart-pointer/rc-arc.html"><strong aria-hidden="true">4.4.4.</strong> Rc 与 Arc 实现 1vN 所有权机制</a></li><li class="chapter-item "><a href="../../advance/smart-pointer/cell-refcell.html"><strong aria-hidden="true">4.4.5.</strong> Cell 与 RefCell 内部可变性</a></li></ol></li><li class="chapter-item "><a href="../../advance/circle-self-ref/intro.html"><strong aria-hidden="true">4.5.</strong> 循环引用与自引用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/circle-self-ref/circle-reference.html"><strong aria-hidden="true">4.5.1.</strong> Weak 与循环引用</a></li><li class="chapter-item "><a href="../../advance/circle-self-ref/self-referential.html"><strong aria-hidden="true">4.5.2.</strong> 结构体中的自引用</a></li></ol></li><li class="chapter-item "><a href="../../advance/concurrency-with-threads/intro.html"><strong aria-hidden="true">4.6.</strong> 多线程并发编程</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/concurrency-with-threads/concurrency-parallelism.html"><strong aria-hidden="true">4.6.1.</strong> 并发和并行</a></li><li class="chapter-item "><a href="../../advance/concurrency-with-threads/thread.html"><strong aria-hidden="true">4.6.2.</strong> 使用多线程</a></li><li class="chapter-item "><a href="../../advance/concurrency-with-threads/message-passing.html"><strong aria-hidden="true">4.6.3.</strong> 线程同步：消息传递</a></li><li class="chapter-item "><a href="../../advance/concurrency-with-threads/sync1.html"><strong aria-hidden="true">4.6.4.</strong> 线程同步：锁、Condvar 和信号量</a></li><li class="chapter-item "><a href="../../advance/concurrency-with-threads/sync2.html"><strong aria-hidden="true">4.6.5.</strong> 线程同步：Atomic 原子操作与内存顺序</a></li><li class="chapter-item "><a href="../../advance/concurrency-with-threads/send-sync.html"><strong aria-hidden="true">4.6.6.</strong> 基于 Send 和 Sync 的线程安全</a></li></ol></li><li class="chapter-item "><a href="../../advance/global-variable.html"><strong aria-hidden="true">4.7.</strong> 全局变量</a></li><li class="chapter-item "><a href="../../advance/errors.html"><strong aria-hidden="true">4.8.</strong> 错误处理</a></li><li class="chapter-item "><a href="../../advance/unsafe/intro.html"><strong aria-hidden="true">4.9.</strong> Unsafe Rust</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/unsafe/superpowers.html"><strong aria-hidden="true">4.9.1.</strong> 五种兵器</a></li><li class="chapter-item "><a href="../../advance/unsafe/inline-asm.html"><strong aria-hidden="true">4.9.2.</strong> 内联汇编</a></li></ol></li><li class="chapter-item "><a href="../../advance/macro.html"><strong aria-hidden="true">4.10.</strong> Macro 宏编程</a></li><li class="chapter-item "><a href="../../advance/async/intro.html"><strong aria-hidden="true">4.11.</strong> async/await 异步编程</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance/async/getting-started.html"><strong aria-hidden="true">4.11.1.</strong> async 编程入门</a></li><li class="chapter-item "><a href="../../advance/async/future-excuting.html"><strong aria-hidden="true">4.11.2.</strong> 底层探秘: Future 执行与任务调度</a></li><li class="chapter-item "><a href="../../advance/async/pin-unpin.html"><strong aria-hidden="true">4.11.3.</strong> 定海神针 Pin 和 Unpin</a></li><li class="chapter-item "><a href="../../advance/async/async-await.html"><strong aria-hidden="true">4.11.4.</strong> async/await 和 Stream 流处理</a></li><li class="chapter-item "><a href="../../advance/async/multi-futures-simultaneous.html"><strong aria-hidden="true">4.11.5.</strong> 同时运行多个 Future</a></li><li class="chapter-item "><a href="../../advance/async/pain-points-and-workarounds.html"><strong aria-hidden="true">4.11.6.</strong> 一些疑难问题的解决办法</a></li><li class="chapter-item "><a href="../../advance/async/web-server.html"><strong aria-hidden="true">4.11.7.</strong> 实践应用：Async Web 服务器</a></li></ol></li></ol></li><li class="chapter-item "><a href="../../advance-practice1/intro.html"><strong aria-hidden="true">5.</strong> 进阶实战1: 实现一个 web 服务器</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance-practice1/web-server.html"><strong aria-hidden="true">5.1.</strong> 单线程版本</a></li><li class="chapter-item "><a href="../../advance-practice1/multi-threads.html"><strong aria-hidden="true">5.2.</strong> 多线程版本</a></li><li class="chapter-item "><a href="../../advance-practice1/graceful-shutdown.html"><strong aria-hidden="true">5.3.</strong> 优雅关闭和资源清理</a></li></ol></li><li class="chapter-item "><a href="../../advance-practice/intro.html"><strong aria-hidden="true">6.</strong> 进阶实战2: 实现一个简单 Redis</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../advance-practice/overview.html"><strong aria-hidden="true">6.1.</strong> tokio 概览</a></li><li class="chapter-item "><a href="../../advance-practice/getting-startted.html"><strong aria-hidden="true">6.2.</strong> 使用初印象</a></li><li class="chapter-item "><a href="../../advance-practice/spawning.html"><strong aria-hidden="true">6.3.</strong> 创建异步任务</a></li><li class="chapter-item "><a href="../../advance-practice/shared-state.html"><strong aria-hidden="true">6.4.</strong> 共享状态</a></li><li class="chapter-item "><a href="../../advance-practice/channels.html"><strong aria-hidden="true">6.5.</strong> 消息传递</a></li><li class="chapter-item "><a href="../../advance-practice/io.html"><strong aria-hidden="true">6.6.</strong> I/O</a></li><li class="chapter-item "><a href="../../advance-practice/frame.html"><strong aria-hidden="true">6.7.</strong> 解析数据帧</a></li><li class="chapter-item "><a href="../../advance-practice/async.html"><strong aria-hidden="true">6.8.</strong> 深入 async</a></li><li class="chapter-item "><a href="../../advance-practice/select.html"><strong aria-hidden="true">6.9.</strong> select</a></li><li class="chapter-item "><a href="../../advance-practice/stream.html"><strong aria-hidden="true">6.10.</strong> 类似迭代器的 Stream</a></li><li class="chapter-item "><a href="../../advance-practice/graceful-shutdown.html"><strong aria-hidden="true">6.11.</strong> 优雅的关闭</a></li><li class="chapter-item "><a href="../../advance-practice/bridging-with-sync.html"><strong aria-hidden="true">6.12.</strong> 异步跟同步共存</a></li></ol></li><li class="chapter-item "><a href="../../difficulties/intro.html"><strong aria-hidden="true">7.</strong> Rust 难点攻关</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../difficulties/slice.html"><strong aria-hidden="true">7.1.</strong> 切片和切片引用</a></li><li class="chapter-item "><a href="../../difficulties/eq.html"><strong aria-hidden="true">7.2.</strong> Eq 和 PartialEq</a></li><li class="chapter-item "><a href="../../difficulties/string.html"><strong aria-hidden="true">7.3.</strong> String、&str 和 str TODO</a></li><li class="chapter-item "><a href="../../difficulties/lifetime.html"><strong aria-hidden="true">7.4.</strong> 作用域、生命周期和 NLL TODO</a></li><li class="chapter-item "><a href="../../difficulties/move-copy.html"><strong aria-hidden="true">7.5.</strong> move、Copy 和 Clone TODO</a></li><li class="chapter-item "><a href="../../advance/difficulties/pointer.html"><strong aria-hidden="true">7.6.</strong> 裸指针、引用和智能指针 TODO</a></li></ol></li><li class="chapter-item "><li class="part-title">常用工具链</li><li class="spacer"></li><li class="chapter-item "><a href="../../test/intro.html"><strong aria-hidden="true">8.</strong> 自动化测试</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../test/write-tests.html"><strong aria-hidden="true">8.1.</strong> 编写测试及控制执行</a></li><li class="chapter-item "><a href="../../test/unit-integration-test.html"><strong aria-hidden="true">8.2.</strong> 单元测试和集成测试</a></li><li class="chapter-item "><a href="../../test/assertion.html"><strong aria-hidden="true">8.3.</strong> 断言 assertion</a></li><li class="chapter-item "><a href="../../test/ci.html"><strong aria-hidden="true">8.4.</strong> 用 GitHub Actions 进行持续集成</a></li><li class="chapter-item "><a href="../../test/benchmark.html"><strong aria-hidden="true">8.5.</strong> 基准测试 benchmark</a></li></ol></li><li class="chapter-item "><a href="../../cargo/intro.html"><strong aria-hidden="true">9.</strong> Cargo 使用指南</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cargo/getting-started.html"><strong aria-hidden="true">9.1.</strong> 上手使用</a></li><li class="chapter-item "><a href="../../cargo/guide/intro.html"><strong aria-hidden="true">9.2.</strong> 基础指南</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cargo/guide/why-exist.html"><strong aria-hidden="true">9.2.1.</strong> 为何会有 Cargo</a></li><li class="chapter-item "><a href="../../cargo/guide/download-package.html"><strong aria-hidden="true">9.2.2.</strong> 下载并构建 Package</a></li><li class="chapter-item "><a href="../../cargo/guide/dependencies.html"><strong aria-hidden="true">9.2.3.</strong> 添加依赖</a></li><li class="chapter-item "><a href="../../cargo/guide/package-layout.html"><strong aria-hidden="true">9.2.4.</strong> Package 目录结构</a></li><li class="chapter-item "><a href="../../cargo/guide/cargo-toml-lock.html"><strong aria-hidden="true">9.2.5.</strong> Cargo.toml vs Cargo.lock</a></li><li class="chapter-item "><a href="../../cargo/guide/tests-ci.html"><strong aria-hidden="true">9.2.6.</strong> 测试和 CI</a></li><li class="chapter-item "><a href="../../cargo/guide/cargo-cache.html"><strong aria-hidden="true">9.2.7.</strong> Cargo 缓存</a></li><li class="chapter-item "><a href="../../cargo/guide/build-cache.html"><strong aria-hidden="true">9.2.8.</strong> Build 缓存</a></li></ol></li><li class="chapter-item "><a href="../../cargo/reference/intro.html"><strong aria-hidden="true">9.3.</strong> 进阶指南</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cargo/reference/specify-deps.html"><strong aria-hidden="true">9.3.1.</strong> 指定依赖项</a></li><li class="chapter-item "><a href="../../cargo/reference/deps-overriding.html"><strong aria-hidden="true">9.3.2.</strong> 依赖覆盖</a></li><li class="chapter-item "><a href="../../cargo/reference/manifest.html"><strong aria-hidden="true">9.3.3.</strong> Cargo.toml 清单详解</a></li><li class="chapter-item "><a href="../../cargo/reference/cargo-target.html"><strong aria-hidden="true">9.3.4.</strong> Cargo Target</a></li><li class="chapter-item "><a href="../../cargo/reference/workspaces.html"><strong aria-hidden="true">9.3.5.</strong> 工作空间 Workspace</a></li><li class="chapter-item "><a href="../../cargo/reference/features/intro.html"><strong aria-hidden="true">9.3.6.</strong> 条件编译 Features</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cargo/reference/features/examples.html"><strong aria-hidden="true">9.3.6.1.</strong> Features 示例</a></li></ol></li><li class="chapter-item "><a href="../../cargo/reference/profiles.html"><strong aria-hidden="true">9.3.7.</strong> 发布配置 Profile</a></li><li class="chapter-item "><a href="../../cargo/reference/configuration.html"><strong aria-hidden="true">9.3.8.</strong> 通过 config.toml 对 Cargo 进行配置</a></li><li class="chapter-item "><a href="../../cargo/reference/publishing-on-crates.io.html"><strong aria-hidden="true">9.3.9.</strong> 发布到 crates.io</a></li><li class="chapter-item "><a href="../../cargo/reference/build-script/intro.html"><strong aria-hidden="true">9.3.10.</strong> 构建脚本 build.rs</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cargo/reference/build-script/examples.html"><strong aria-hidden="true">9.3.10.1.</strong> 构建脚本示例</a></li></ol></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">开发实践</li><li class="spacer"></li><li class="chapter-item "><a href="../../usecases/intro.html"><strong aria-hidden="true">10.</strong> 企业落地实践</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usecases/aws-rust.html"><strong aria-hidden="true">10.1.</strong> AWS 为何这么喜欢 Rust?</a></li></ol></li><li class="chapter-item "><a href="../../logs/intro.html"><strong aria-hidden="true">11.</strong> 日志和监控</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../logs/about-log.html"><strong aria-hidden="true">11.1.</strong> 日志详解</a></li><li class="chapter-item "><a href="../../logs/log.html"><strong aria-hidden="true">11.2.</strong> 日志门面 log</a></li><li class="chapter-item "><a href="../../logs/tracing.html"><strong aria-hidden="true">11.3.</strong> 使用 tracing 记录日志</a></li><li class="chapter-item "><a href="../../logs/tracing-logger.html"><strong aria-hidden="true">11.4.</strong> 自定义 tracing 的输出格式</a></li><li class="chapter-item "><a href="../../logs/observe/intro.html"><strong aria-hidden="true">11.5.</strong> 监控</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../logs/observe/about-observe.html"><strong aria-hidden="true">11.5.1.</strong> 可观测性</a></li><li class="chapter-item "><a href="../../logs/observe/trace.html"><strong aria-hidden="true">11.5.2.</strong> 分布式追踪</a></li></ol></li></ol></li><li class="chapter-item "><a href="../../practice/intro.html"><strong aria-hidden="true">12.</strong> Rust 最佳实践</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../practice/third-party-libs.html"><strong aria-hidden="true">12.1.</strong> 日常开发三方库精选</a></li><li class="chapter-item "><a href="../../practice/naming.html"><strong aria-hidden="true">12.2.</strong> 命名规范</a></li><li class="chapter-item "><a href="../../practice/interview.html"><strong aria-hidden="true">12.3.</strong> 面试经验</a></li><li class="chapter-item "><a href="../../practice/best-pratice.html"><strong aria-hidden="true">12.4.</strong> 代码开发实践 todo</a></li></ol></li><li class="chapter-item "><a href="../../too-many-lists/intro.html"><strong aria-hidden="true">13.</strong> 手把手带你实现链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/do-we-need-it.html"><strong aria-hidden="true">13.1.</strong> 我们到底需不需要链表</a></li><li class="chapter-item "><a href="../../too-many-lists/bad-stack/intro.html"><strong aria-hidden="true">13.2.</strong> 不太优秀的单向链表：栈</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/bad-stack/layout.html"><strong aria-hidden="true">13.2.1.</strong> 数据布局</a></li><li class="chapter-item "><a href="../../too-many-lists/bad-stack/basic-operations.html"><strong aria-hidden="true">13.2.2.</strong> 基本操作</a></li><li class="chapter-item "><a href="../../too-many-lists/bad-stack/final-code.html"><strong aria-hidden="true">13.2.3.</strong> 最后实现</a></li></ol></li><li class="chapter-item "><a href="../../too-many-lists/ok-stack/intro.html"><strong aria-hidden="true">13.3.</strong> 还可以的单向链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/ok-stack/type-optimizing.html"><strong aria-hidden="true">13.3.1.</strong> 优化类型定义</a></li><li class="chapter-item "><a href="../../too-many-lists/ok-stack/peek.html"><strong aria-hidden="true">13.3.2.</strong> 定义 Peek 函数</a></li><li class="chapter-item "><a href="../../too-many-lists/ok-stack/iter.html"><strong aria-hidden="true">13.3.3.</strong> IntoIter 和 Iter</a></li><li class="chapter-item "><a href="../../too-many-lists/ok-stack/itermut.html"><strong aria-hidden="true">13.3.4.</strong> IterMut 以及完整代码</a></li></ol></li><li class="chapter-item "><a href="../../too-many-lists/persistent-stack/intro.html"><strong aria-hidden="true">13.4.</strong> 持久化单向链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/persistent-stack/layout.html"><strong aria-hidden="true">13.4.1.</strong> 数据布局和基本操作</a></li><li class="chapter-item "><a href="../../too-many-lists/persistent-stack/drop-arc.html"><strong aria-hidden="true">13.4.2.</strong> Drop、Arc 及完整代码</a></li></ol></li><li class="chapter-item "><a href="../../too-many-lists/deque/intro.html"><strong aria-hidden="true">13.5.</strong> 不咋样的双端队列</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/deque/layout.html"><strong aria-hidden="true">13.5.1.</strong> 数据布局和基本操作</a></li><li class="chapter-item "><a href="../../too-many-lists/deque/peek.html"><strong aria-hidden="true">13.5.2.</strong> Peek</a></li><li class="chapter-item "><a href="../../too-many-lists/deque/symmetric.html"><strong aria-hidden="true">13.5.3.</strong> 基本操作的对称镜像</a></li><li class="chapter-item "><a href="../../too-many-lists/deque/iterator.html"><strong aria-hidden="true">13.5.4.</strong> 迭代器</a></li><li class="chapter-item "><a href="../../too-many-lists/deque/final-code.html"><strong aria-hidden="true">13.5.5.</strong> 最终代码</a></li></ol></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/intro.html"><strong aria-hidden="true">13.6.</strong> 不错的 unsafe 队列</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/layout.html"><strong aria-hidden="true">13.6.1.</strong> 数据布局</a></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/basics.html"><strong aria-hidden="true">13.6.2.</strong> 基本操作</a></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/miri.html"><strong aria-hidden="true">13.6.3.</strong> Miri</a></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/stacked-borrow.html"><strong aria-hidden="true">13.6.4.</strong> 栈借用</a></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/testing-stacked-borrow.html"><strong aria-hidden="true">13.6.5.</strong> 测试栈借用</a></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/layout2.html"><strong aria-hidden="true">13.6.6.</strong> 数据布局 2</a></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/extra-junk.html"><strong aria-hidden="true">13.6.7.</strong> 额外的操作</a></li><li class="chapter-item "><a href="../../too-many-lists/unsafe-queue/final-code.html"><strong aria-hidden="true">13.6.8.</strong> 最终代码</a></li></ol></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/intro.html"><strong aria-hidden="true">13.7.</strong> 生产级的双向 unsafe 队列</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/layout.html"><strong aria-hidden="true">13.7.1.</strong> 数据布局</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/variance-and-phantomData.html"><strong aria-hidden="true">13.7.2.</strong> 型变与子类型</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/basics.html"><strong aria-hidden="true">13.7.3.</strong> 基础结构</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/drop-and-panic-safety.html"><strong aria-hidden="true">13.7.4.</strong> 恐慌与安全</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/boring-combinatorics.html"><strong aria-hidden="true">13.7.5.</strong> 无聊的组合</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/filling-in-random-bits.html"><strong aria-hidden="true">13.7.6.</strong> 其它特征</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/testing.html"><strong aria-hidden="true">13.7.7.</strong> 测试</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/send-sync-and-compile-tests.html"><strong aria-hidden="true">13.7.8.</strong> Send,Sync和编译测试</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/implementing-cursors.html"><strong aria-hidden="true">13.7.9.</strong> 实现游标</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/testing-cursors.html"><strong aria-hidden="true">13.7.10.</strong> 测试游标</a></li><li class="chapter-item "><a href="../../too-many-lists/production-unsafe-deque/final-code.html"><strong aria-hidden="true">13.7.11.</strong> 最终代码</a></li></ol></li><li class="chapter-item "><a href="../../too-many-lists/advanced-lists/intro.html"><strong aria-hidden="true">13.8.</strong> 使用高级技巧实现链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../too-many-lists/advanced-lists/double-singly.html"><strong aria-hidden="true">13.8.1.</strong> 双单向链表</a></li><li class="chapter-item "><a href="../../too-many-lists/advanced-lists/stack-allocated.html"><strong aria-hidden="true">13.8.2.</strong> 栈上的链表</a></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">攻克编译错误</li><li class="spacer"></li><li class="chapter-item "><a href="../../compiler/intro.html"><strong aria-hidden="true">14.</strong> 征服编译错误</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../compiler/fight-with-compiler/intro.html"><strong aria-hidden="true">14.1.</strong> 对抗编译检查</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../compiler/fight-with-compiler/lifetime/intro.html"><strong aria-hidden="true">14.1.1.</strong> 生命周期</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../compiler/fight-with-compiler/lifetime/too-long1.html"><strong aria-hidden="true">14.1.1.1.</strong> 生命周期过大-01</a></li><li class="chapter-item "><a href="../../compiler/fight-with-compiler/lifetime/too-long2.html"><strong aria-hidden="true">14.1.1.2.</strong> 生命周期过大-02</a></li><li class="chapter-item "><a href="../../compiler/fight-with-compiler/lifetime/loop.html"><strong aria-hidden="true">14.1.1.3.</strong> 循环中的生命周期</a></li><li class="chapter-item "><a href="../../compiler/fight-with-compiler/lifetime/closure-with-static.html"><strong aria-hidden="true">14.1.1.4.</strong> 闭包碰到特征对象-01</a></li></ol></li><li class="chapter-item "><a href="../../compiler/fight-with-compiler/borrowing/intro.html"><strong aria-hidden="true">14.1.2.</strong> 重复借用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../compiler/fight-with-compiler/borrowing/ref-exist-in-out-fn.html"><strong aria-hidden="true">14.1.2.1.</strong> 同时在函数内外使用引用</a></li><li class="chapter-item "><a href="../../compiler/fight-with-compiler/borrowing/borrow-distinct-fields-of-struct.html"><strong aria-hidden="true">14.1.2.2.</strong> 智能指针引起的重复借用错误</a></li></ol></li><li class="chapter-item "><a href="../../compiler/fight-with-compiler/unconstrained.html"><strong aria-hidden="true">14.1.3.</strong> 类型未限制(todo)</a></li><li class="chapter-item "><a href="../../compiler/fight-with-compiler/phantom-data.html"><strong aria-hidden="true">14.1.4.</strong> 幽灵数据(todo)</a></li></ol></li><li class="chapter-item "><a href="../../compiler/pitfalls/index.html"><strong aria-hidden="true">14.2.</strong> Rust 常见陷阱</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../compiler/pitfalls/use-vec-in-for.html"><strong aria-hidden="true">14.2.1.</strong> for 循环中使用外部数组</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/stack-overflow.html"><strong aria-hidden="true">14.2.2.</strong> 线程类型导致的栈溢出</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/arithmetic-overflow.html"><strong aria-hidden="true">14.2.3.</strong> 算术溢出导致的 panic</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/closure-with-lifetime.html"><strong aria-hidden="true">14.2.4.</strong> 闭包中奇怪的生命周期</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/the-disabled-mutability.html"><strong aria-hidden="true">14.2.5.</strong> 可变变量不可变？</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/multiple-mutable-references.html"><strong aria-hidden="true">14.2.6.</strong> 可变借用失败引发的深入思考</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/lazy-iterators.html"><strong aria-hidden="true">14.2.7.</strong> 不太勤快的迭代器</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/weird-ranges.html"><strong aria-hidden="true">14.2.8.</strong> 奇怪的序列 x..y</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/iterator-everywhere.html"><strong aria-hidden="true">14.2.9.</strong> 无处不在的迭代器</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/main-with-channel-blocked.html"><strong aria-hidden="true">14.2.10.</strong> 线程间传递消息导致主线程无法结束</a></li><li class="chapter-item "><a href="../../compiler/pitfalls/utf8-performance.html"><strong aria-hidden="true">14.2.11.</strong> 警惕 UTF-8 引发的性能隐患</a></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">性能优化</li><li class="spacer"></li><li class="chapter-item "><a href="../../profiling/intro.html"><strong aria-hidden="true">15.</strong> Rust 性能优化 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../profiling/memory/intro.html"><strong aria-hidden="true">15.1.</strong> 深入内存 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../profiling/memory/pointer-ref.html"><strong aria-hidden="true">15.1.1.</strong> 指针和引用 todo</a></li><li class="chapter-item "><a href="../../profiling/memory/uninit.html"><strong aria-hidden="true">15.1.2.</strong> 未初始化内存 todo</a></li><li class="chapter-item "><a href="../../profiling/memory/allocation.html"><strong aria-hidden="true">15.1.3.</strong> 内存分配 todo</a></li><li class="chapter-item "><a href="../../profiling/memory/layout.html"><strong aria-hidden="true">15.1.4.</strong> 内存布局 todo</a></li><li class="chapter-item "><a href="../../profiling/memory/virtual.html"><strong aria-hidden="true">15.1.5.</strong> 虚拟内存 todo</a></li></ol></li><li class="chapter-item "><a href="../../profiling/performance/intro.html"><strong aria-hidden="true">15.2.</strong> 性能调优 doing</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../profiling/performance/string.html"><strong aria-hidden="true">15.2.1.</strong> 字符串操作性能</a></li><li class="chapter-item "><a href="../../profiling/performance/deep-into-move.html"><strong aria-hidden="true">15.2.2.</strong> 深入理解 move</a></li><li class="chapter-item "><a href="../../profiling/performance/early-optimise.html"><strong aria-hidden="true">15.2.3.</strong> 糟糕的提前优化 todo</a></li><li class="chapter-item "><a href="../../profiling/performance/clone-copy.html"><strong aria-hidden="true">15.2.4.</strong> Clone 和 Copy todo</a></li><li class="chapter-item "><a href="../../profiling/performance/runtime-check.html"><strong aria-hidden="true">15.2.5.</strong> 减少 Runtime check(todo)</a></li><li class="chapter-item "><a href="../../profiling/performance/cpu-cache.html"><strong aria-hidden="true">15.2.6.</strong> CPU 缓存性能优化 todo</a></li><li class="chapter-item "><a href="../../profiling/performance/calculate.html"><strong aria-hidden="true">15.2.7.</strong> 计算性能优化 todo</a></li><li class="chapter-item "><a href="../../profiling/performance/heap-stack.html"><strong aria-hidden="true">15.2.8.</strong> 堆和栈 todo</a></li><li class="chapter-item "><a href="../../profiling/performance/allocator.html"><strong aria-hidden="true">15.2.9.</strong> 内存 allocator todo</a></li><li class="chapter-item "><a href="../../profiling/performance/tools.html"><strong aria-hidden="true">15.2.10.</strong> 常用性能测试工具 todo</a></li><li class="chapter-item "><a href="../../profiling/performance/enum.html"><strong aria-hidden="true">15.2.11.</strong> Enum 内存优化 todo</a></li></ol></li><li class="chapter-item "><a href="../../profiling/compiler/intro.html"><strong aria-hidden="true">15.3.</strong> 编译优化 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../profiling/compiler/llvm.html"><strong aria-hidden="true">15.3.1.</strong> LLVM todo</a></li><li class="chapter-item "><a href="../../profiling/compiler/attributes.html"><strong aria-hidden="true">15.3.2.</strong> 常见属性标记 todo</a></li><li class="chapter-item "><a href="../../profiling/compiler/speed-up.html"><strong aria-hidden="true">15.3.3.</strong> 提升编译速度 todo</a></li><li class="chapter-item "><a href="../../profiling/compiler/optimization/intro.html"><strong aria-hidden="true">15.3.4.</strong> 编译器优化 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../profiling/compiler/optimization/option.html"><strong aria-hidden="true">15.3.4.1.</strong> Option 枚举 todo</a></li></ol></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">附录</li><li class="spacer"></li><li class="chapter-item "><div><strong aria-hidden="true">16.</strong> Appendix</div><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../appendix/keywords.html"><strong aria-hidden="true">16.1.</strong> 关键字</a></li><li class="chapter-item "><a href="../../appendix/operators.html"><strong aria-hidden="true">16.2.</strong> 运算符与符号</a></li><li class="chapter-item "><a href="../../appendix/expressions.html"><strong aria-hidden="true">16.3.</strong> 表达式</a></li><li class="chapter-item "><a href="../../appendix/derive.html"><strong aria-hidden="true">16.4.</strong> 派生特征 trait</a></li><li class="chapter-item "><a href="../../appendix/prelude.html"><strong aria-hidden="true">16.5.</strong> prelude 模块 todo</a></li><li class="chapter-item "><a href="../../appendix/rust-version.html"><strong aria-hidden="true">16.6.</strong> Rust 版本说明</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/intro.html"><strong aria-hidden="true">16.7.</strong> Rust 历次版本更新解读</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../appendix/rust-versions/1.58.html"><strong aria-hidden="true">16.7.1.</strong> 1.58</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.59.html"><strong aria-hidden="true">16.7.2.</strong> 1.59</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.60.html"><strong aria-hidden="true">16.7.3.</strong> 1.60</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.61.html"><strong aria-hidden="true">16.7.4.</strong> 1.61</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.62.html"><strong aria-hidden="true">16.7.5.</strong> 1.62</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.63.html"><strong aria-hidden="true">16.7.6.</strong> 1.63</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.64.html"><strong aria-hidden="true">16.7.7.</strong> 1.64</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.65.html"><strong aria-hidden="true">16.7.8.</strong> 1.65</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.66.html"><strong aria-hidden="true">16.7.9.</strong> 1.66</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.67.html"><strong aria-hidden="true">16.7.10.</strong> 1.67</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.68.html"><strong aria-hidden="true">16.7.11.</strong> 1.68</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.69.html"><strong aria-hidden="true">16.7.12.</strong> 1.69</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.70.html"><strong aria-hidden="true">16.7.13.</strong> 1.70</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.71.html"><strong aria-hidden="true">16.7.14.</strong> 1.71</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.72.html"><strong aria-hidden="true">16.7.15.</strong> 1.72</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.73.html"><strong aria-hidden="true">16.7.16.</strong> 1.73</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.74.html"><strong aria-hidden="true">16.7.17.</strong> 1.74</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.75.html"><strong aria-hidden="true">16.7.18.</strong> 1.75</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.76.html"><strong aria-hidden="true">16.7.19.</strong> 1.76</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.77.html"><strong aria-hidden="true">16.7.20.</strong> 1.77</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.78.html"><strong aria-hidden="true">16.7.21.</strong> 1.78</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.79.html"><strong aria-hidden="true">16.7.22.</strong> 1.79</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.80.html"><strong aria-hidden="true">16.7.23.</strong> 1.80</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.81.html"><strong aria-hidden="true">16.7.24.</strong> 1.81</a></li><li class="chapter-item "><a href="../../appendix/rust-versions/1.82.html"><strong aria-hidden="true">16.7.25.</strong> 1.82</a></li></ol></li></ol></li></ol>
|
|
|
</div>
|
|
|
<div id="sidebar-resize-handle" class="sidebar-resize-handle">
|
|
|
<div class="sidebar-resize-indicator"></div>
|
|
|
</div>
|
|
|
</nav>
|
|
|
|
|
|
<!-- Track and set sidebar scroll position -->
|
|
|
<script>
|
|
|
var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
|
|
|
sidebarScrollbox.addEventListener('click', function(e) {
|
|
|
if (e.target.tagName === 'A') {
|
|
|
sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
|
|
|
}
|
|
|
}, { passive: true });
|
|
|
var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
|
|
|
sessionStorage.removeItem('sidebar-scroll');
|
|
|
if (sidebarScrollTop) {
|
|
|
// preserve sidebar scroll position when navigating via links within sidebar
|
|
|
sidebarScrollbox.scrollTop = sidebarScrollTop;
|
|
|
} else {
|
|
|
// scroll sidebar to current active section when navigating via "next/previous chapter" buttons
|
|
|
var activeSection = document.querySelector('#sidebar .active');
|
|
|
if (activeSection) {
|
|
|
activeSection.scrollIntoView({ block: 'center' });
|
|
|
}
|
|
|
}
|
|
|
</script>
|
|
|
|
|
|
<div id="page-wrapper" class="page-wrapper">
|
|
|
|
|
|
<div class="page">
|
|
|
<div id="menu-bar-hover-placeholder"></div>
|
|
|
<div id="menu-bar" class="menu-bar sticky">
|
|
|
<div class="left-buttons">
|
|
|
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
|
|
<i class="fa fa-bars"></i>
|
|
|
</label>
|
|
|
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
|
|
<i class="fa fa-paint-brush"></i>
|
|
|
</button>
|
|
|
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
|
|
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
|
|
|
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
|
|
|
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
|
|
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
|
|
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
|
|
</ul>
|
|
|
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
|
|
|
<i class="fa fa-search"></i>
|
|
|
</button>
|
|
|
</div>
|
|
|
|
|
|
<h1 class="menu-title">Rust语言圣经(Rust Course)</h1>
|
|
|
|
|
|
<div class="right-buttons">
|
|
|
<a href="../../print.html" title="Print this book" aria-label="Print this book">
|
|
|
<i id="print-button" class="fa fa-print"></i>
|
|
|
</a>
|
|
|
<a href="https://github.com/sunface/rust-course" title="Git repository" aria-label="Git repository">
|
|
|
<i id="git-repository-button" class="fa fa-github"></i>
|
|
|
</a>
|
|
|
<a href="https://github.com/sunface/rust-course/edit/main/src/basic/result-error/result.md" title="Suggest an edit" aria-label="Suggest an edit">
|
|
|
<i id="git-edit-button" class="fa fa-edit"></i>
|
|
|
</a>
|
|
|
|
|
|
</div>
|
|
|
</div>
|
|
|
|
|
|
<div id="search-wrapper" class="hidden">
|
|
|
<form id="searchbar-outer" class="searchbar-outer">
|
|
|
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
|
|
|
</form>
|
|
|
<div id="searchresults-outer" class="searchresults-outer hidden">
|
|
|
<div id="searchresults-header" class="searchresults-header"></div>
|
|
|
<ul id="searchresults">
|
|
|
</ul>
|
|
|
</div>
|
|
|
</div>
|
|
|
|
|
|
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
|
|
<script>
|
|
|
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
|
|
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
|
|
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
|
|
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
|
|
});
|
|
|
</script>
|
|
|
|
|
|
<div id="content" class="content">
|
|
|
<!-- Page table of contents -->
|
|
|
<div class="sidetoc"><nav class="pagetoc"></nav></div>
|
|
|
<main>
|
|
|
<h1 id="可恢复的错误-result"><a class="header" href="#可恢复的错误-result">可恢复的错误 Result</a></h1>
|
|
|
<p>还记得上一节中，提到的关于文件读取的思考题吧？当时我们解决了读取文件时遇到不可恢复错误该怎么处理的问题，现在来看看，读取过程中，正常返回和遇到可以恢复的错误时该如何处理。</p>
|
|
|
<p>假设，我们有一台消息服务器，每个用户都通过 websocket 连接到该服务器来接收和发送消息，该过程就涉及到 socket 文件的读写，那么此时，如果一个用户的读写发生了错误，显然不能直接 <code>panic</code>，否则服务器会直接崩溃，所有用户都会断开连接，因此我们需要一种更温和的错误处理方式：<code>Result<T, E></code>。</p>
|
|
|
<p>之前章节有提到过，<code>Result<T, E></code> 是一个枚举类型，定义如下：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>enum Result<T, E> {
|
|
|
Ok(T),
|
|
|
Err(E),
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>泛型参数 <code>T</code> 代表成功时存入的正确值的类型，存放方式是 <code>Ok(T)</code>，<code>E</code> 代表错误时存入的错误值，存放方式是 <code>Err(E)</code>，枯燥的讲解永远不及代码生动准确，因此先来看下打开文件的例子：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::fs::File;
|
|
|
|
|
|
fn main() {
|
|
|
let f = File::open("hello.txt");
|
|
|
}</code></pre></pre>
|
|
|
<p>以上 <code>File::open</code> 返回一个 <code>Result</code> 类型，那么问题来了：</p>
|
|
|
<blockquote>
|
|
|
<h4 id="如何获知变量类型或者函数的返回类型"><a class="header" href="#如何获知变量类型或者函数的返回类型">如何获知变量类型或者函数的返回类型</a></h4>
|
|
|
<p>有几种常用的方式，此处更推荐第二种方法：</p>
|
|
|
<ul>
|
|
|
<li>第一种是查询标准库或者三方库文档，搜索 <code>File</code>，然后找到它的 <code>open</code> 方法</li>
|
|
|
<li>在 <a href="https://course.rs/first-try/editor.html">Rust IDE</a> 章节，我们推荐了 <code>VSCode</code> IDE 和 <code>rust-analyzer</code> 插件，如果你成功安装的话，那么就可以在 <code>VSCode</code> 中很方便的通过代码跳转的方式查看代码，同时 <code>rust-analyzer</code> 插件还会对代码中的类型进行标注，非常方便好用！</li>
|
|
|
<li>你还可以尝试故意标记一个错误的类型，然后让编译器告诉你：</li>
|
|
|
</ul>
|
|
|
</blockquote>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>let f: u32 = File::open("hello.txt");
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>错误提示如下：</p>
|
|
|
<pre><code class="language-console">error[E0308]: mismatched types
|
|
|
--> src/main.rs:4:18
|
|
|
|
|
|
|
4 | let f: u32 = File::open("hello.txt");
|
|
|
| ^^^^^^^^^^^^^^^^^^^^^^^ expected u32, found enum
|
|
|
`std::result::Result`
|
|
|
|
|
|
|
= note: expected type `u32`
|
|
|
found type `std::result::Result<std::fs::File, std::io::Error>`
|
|
|
</code></pre>
|
|
|
<p>上面代码，故意将 <code>f</code> 类型标记成整形，编译器立刻不乐意了，你是在忽悠我吗？打开文件操作返回一个整形？来，大哥来告诉你返回什么：<code>std::result::Result<std::fs::File, std::io::Error></code>，我的天呐，怎么这么长的类型！</p>
|
|
|
<p>别慌，其实很简单，首先 <code>Result</code> 本身是定义在 <code>std::result</code> 中的，但是因为 <code>Result</code> 很常用，所以就被包含在了 <a href="https://course.rs/appendix/prelude.html"><code>prelude</code></a> 中（将常用的东东提前引入到当前作用域内），因此无需手动引入 <code>std::result::Result</code>，那么返回类型可以简化为 <code>Result<std::fs::File,std::io::Error></code>，你看看是不是很像标准的 <code>Result<T, E></code> 枚举定义？只不过 <code>T</code> 被替换成了具体的类型 <code>std::fs::File</code>，是一个文件句柄类型，<code>E</code> 被替换成 <code>std::io::Error</code>，是一个 IO 错误类型。</p>
|
|
|
<p>这个返回值类型说明 <code>File::open</code> 调用如果成功则返回一个可以进行读写的文件句柄，如果失败，则返回一个 IO 错误：文件不存在或者没有访问文件的权限等。总之 <code>File::open</code> 需要一个方式告知调用者是成功还是失败，并同时返回具体的文件句柄（成功）或错误信息（失败），万幸的是，这些信息可以通过 <code>Result</code> 枚举提供：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::fs::File;
|
|
|
|
|
|
fn main() {
|
|
|
let f = File::open("hello.txt");
|
|
|
|
|
|
let f = match f {
|
|
|
Ok(file) => file,
|
|
|
Err(error) => {
|
|
|
panic!("Problem opening the file: {:?}", error)
|
|
|
},
|
|
|
};
|
|
|
}</code></pre></pre>
|
|
|
<p>代码很清晰，对打开文件后的 <code>Result<T, E></code> 类型进行匹配取值，如果是成功，则将 <code>Ok(file)</code> 中存放的的文件句柄 <code>file</code> 赋值给 <code>f</code>，如果失败，则将 <code>Err(error)</code> 中存放的错误信息 <code>error</code> 使用 <code>panic</code> 抛出来，进而结束程序，这非常符合上文提到过的 <code>panic</code> 使用场景。</p>
|
|
|
<p>好吧，也没有那么合理 :)</p>
|
|
|
<h2 id="对返回的错误进行处理"><a class="header" href="#对返回的错误进行处理">对返回的错误进行处理</a></h2>
|
|
|
<p>直接 <code>panic</code> 还是过于粗暴，因为实际上 IO 的错误有很多种，我们需要对部分错误进行特殊处理，而不是所有错误都直接崩溃：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::fs::File;
|
|
|
use std::io::ErrorKind;
|
|
|
|
|
|
fn main() {
|
|
|
let f = File::open("hello.txt");
|
|
|
|
|
|
let f = match f {
|
|
|
Ok(file) => file,
|
|
|
Err(error) => match error.kind() {
|
|
|
ErrorKind::NotFound => match File::create("hello.txt") {
|
|
|
Ok(fc) => fc,
|
|
|
Err(e) => panic!("Problem creating the file: {:?}", e),
|
|
|
},
|
|
|
other_error => panic!("Problem opening the file: {:?}", other_error),
|
|
|
},
|
|
|
};
|
|
|
}</code></pre></pre>
|
|
|
<p>上面代码在匹配出 <code>error</code> 后，又对 <code>error</code> 进行了详细的匹配解析，最终结果：</p>
|
|
|
<ul>
|
|
|
<li>如果是文件不存在错误 <code>ErrorKind::NotFound</code>，就创建文件，这里创建文件<code>File::create</code> 也是返回 <code>Result</code>，因此继续用 <code>match</code> 对其结果进行处理：创建成功，将新的文件句柄赋值给 <code>f</code>，如果失败，则 <code>panic</code></li>
|
|
|
<li>剩下的错误，一律 <code>panic</code></li>
|
|
|
</ul>
|
|
|
<p>虽然很清晰，但是代码还是有些啰嗦，我们会在<a href="https://course.rs/advance/errors.html">简化错误处理</a>一章重点讲述如何写出更优雅的错误。</p>
|
|
|
<h2 id="失败就-panic-unwrap-和-expect"><a class="header" href="#失败就-panic-unwrap-和-expect">失败就 panic: unwrap 和 expect</a></h2>
|
|
|
<p>上一节中，已经看到过这两兄弟的简单介绍，这里再来回顾下。</p>
|
|
|
<p>在不需要处理错误的场景，例如写原型、示例时，我们不想使用 <code>match</code> 去匹配 <code>Result<T, E> </code> 以获取其中的 <code>T</code> 值，因为 <code>match</code> 的穷尽匹配特性，你总要去处理下 <code>Err</code> 分支。那么有没有办法简化这个过程？有，答案就是 <code>unwrap</code> 和 <code>expect</code>。</p>
|
|
|
<p>它们的作用就是，如果返回成功，就将 <code>Ok(T)</code> 中的值取出来，如果失败，就直接 <code>panic</code>，真的勇士绝不多 BB，直接崩溃。</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::fs::File;
|
|
|
|
|
|
fn main() {
|
|
|
let f = File::open("hello.txt").unwrap();
|
|
|
}</code></pre></pre>
|
|
|
<p>如果调用这段代码时 <em>hello.txt</em> 文件不存在，那么 <code>unwrap</code> 就将直接 <code>panic</code>：</p>
|
|
|
<pre><code class="language-console">thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }', src/main.rs:4:37
|
|
|
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
|
|
|
</code></pre>
|
|
|
<p><code>expect</code> 跟 <code>unwrap</code> 很像，也是遇到错误直接 <code>panic</code>, 但是会带上自定义的错误提示信息，相当于重载了错误打印的函数：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::fs::File;
|
|
|
|
|
|
fn main() {
|
|
|
let f = File::open("hello.txt").expect("Failed to open hello.txt");
|
|
|
}</code></pre></pre>
|
|
|
<p>报错如下：</p>
|
|
|
<pre><code class="language-console">thread 'main' panicked at 'Failed to open hello.txt: Os { code: 2, kind: NotFound, message: "No such file or directory" }', src/main.rs:4:37
|
|
|
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
|
|
|
</code></pre>
|
|
|
<p>可以看出，<code>expect</code> 相比 <code>unwrap</code> 能提供更精确的错误信息，在有些场景也会更加实用。</p>
|
|
|
<h2 id="传播错误"><a class="header" href="#传播错误">传播错误</a></h2>
|
|
|
<p>咱们的程序几乎不太可能只有 <code>A->B</code> 形式的函数调用，一个设计良好的程序，一个功能涉及十几层的函数调用都有可能。而错误处理也往往不是哪里调用出错，就在哪里处理，实际应用中，大概率会把错误层层上传然后交给调用链的上游函数进行处理，错误传播将极为常见。</p>
|
|
|
<p>例如以下函数从文件中读取用户名，然后将结果进行返回：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>use std::fs::File;
|
|
|
use std::io::{self, Read};
|
|
|
|
|
|
fn read_username_from_file() -> Result<String, io::Error> {
|
|
|
// 打开文件，f是`Result<文件句柄,io::Error>`
|
|
|
let f = File::open("hello.txt");
|
|
|
|
|
|
let mut f = match f {
|
|
|
// 打开文件成功，将file句柄赋值给f
|
|
|
Ok(file) => file,
|
|
|
// 打开文件失败，将错误返回(向上传播)
|
|
|
Err(e) => return Err(e),
|
|
|
};
|
|
|
// 创建动态字符串s
|
|
|
let mut s = String::new();
|
|
|
// 从f文件句柄读取数据并写入s中
|
|
|
match f.read_to_string(&mut s) {
|
|
|
// 读取成功，返回Ok封装的字符串
|
|
|
Ok(_) => Ok(s),
|
|
|
// 将错误向上传播
|
|
|
Err(e) => Err(e),
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>有几点值得注意：</p>
|
|
|
<ul>
|
|
|
<li>该函数返回一个 <code>Result<String, io::Error></code> 类型，当读取用户名成功时，返回 <code>Ok(String)</code>，失败时，返回 <code>Err(io:Error)</code></li>
|
|
|
<li><code>File::open</code> 和 <code>f.read_to_string</code> 返回的 <code>Result<T, E></code> 中的 <code>E</code> 就是 <code>io::Error</code></li>
|
|
|
</ul>
|
|
|
<p>由此可见，该函数将 <code>io::Error</code> 的错误往上进行传播，该函数的调用者最终会对 <code>Result<String,io::Error></code> 进行再处理，至于怎么处理就是调用者的事，如果是错误，它可以选择继续向上传播错误，也可以直接 <code>panic</code>，亦或将具体的错误原因包装后写入 socket 中呈现给终端用户。</p>
|
|
|
<p>但是上面的代码也有自己的问题，那就是太长了（优秀的程序员身上的优点极多，其中最大的优点就是<em>懒</em>），我自认为也有那么一点点优秀，因此见不得这么啰嗦的代码，下面咱们来讲讲如何简化它。</p>
|
|
|
<h3 id="传播界的大明星-"><a class="header" href="#传播界的大明星-">传播界的大明星: ?</a></h3>
|
|
|
<p>大明星出场，必须得有排面，来看看 <code>?</code> 的排面：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>use std::fs::File;
|
|
|
use std::io;
|
|
|
use std::io::Read;
|
|
|
|
|
|
fn read_username_from_file() -> Result<String, io::Error> {
|
|
|
let mut f = File::open("hello.txt")?;
|
|
|
let mut s = String::new();
|
|
|
f.read_to_string(&mut s)?;
|
|
|
Ok(s)
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>看到没，这就是排面，相比前面的 <code>match</code> 处理错误的函数，代码直接减少了一半不止，但是，一山更比一山难，看不懂啊！</p>
|
|
|
<p>其实 <code>?</code> 就是一个宏，它的作用跟上面的 <code>match</code> 几乎一模一样：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>let mut f = match f {
|
|
|
// 打开文件成功，将file句柄赋值给f
|
|
|
Ok(file) => file,
|
|
|
// 打开文件失败，将错误返回(向上传播)
|
|
|
Err(e) => return Err(e),
|
|
|
};
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>如果结果是 <code>Ok(T)</code>，则把 <code>T</code> 赋值给 <code>f</code>，如果结果是 <code>Err(E)</code>，则返回该错误，所以 <code>?</code> 特别适合用来传播错误。</p>
|
|
|
<p>虽然 <code>?</code> 和 <code>match</code> 功能一致，但是事实上 <code>?</code> 会更胜一筹。何解？</p>
|
|
|
<p>想象一下，一个设计良好的系统中，肯定有自定义的错误特征，错误之间很可能会存在上下级关系，例如标准库中的 <code>std::io::Error </code>和 <code>std::error::Error</code>，前者是 IO 相关的错误结构体，后者是一个最最通用的标准错误特征，同时前者实现了后者，因此 <code>std::io::Error</code> 可以转换为 <code>std:error::Error</code>。</p>
|
|
|
<p>明白了以上的错误转换，<code>?</code> 的更胜一筹就很好理解了，它可以自动进行类型提升（转换）：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>fn open_file() -> Result<File, Box<dyn std::error::Error>> {
|
|
|
let mut f = File::open("hello.txt")?;
|
|
|
Ok(f)
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>上面代码中 <code>File::open</code> 报错时返回的错误是 <code>std::io::Error</code> 类型，但是 <code>open_file</code> 函数返回的错误类型是 <code>std::error::Error</code> 的特征对象，可以看到一个错误类型通过 <code>?</code> 返回后，变成了另一个错误类型，这就是 <code>?</code> 的神奇之处。</p>
|
|
|
<p>根本原因是在于标准库中定义的 <code>From</code> 特征，该特征有一个方法 <code>from</code>，用于把一个类型转成另外一个类型，<code>?</code> 可以自动调用该方法，然后进行隐式类型转换。因此只要函数返回的错误 <code>ReturnError</code> 实现了 <code>From<OtherError></code> 特征，那么 <code>?</code> 就会自动把 <code>OtherError</code> 转换为 <code>ReturnError</code>。</p>
|
|
|
<p>这种转换非常好用，意味着你可以用一个大而全的 <code>ReturnError</code> 来覆盖所有错误类型，只需要为各种子错误类型实现这种转换即可。</p>
|
|
|
<p>强中自有强中手，一码更比一码短：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>use std::fs::File;
|
|
|
use std::io;
|
|
|
use std::io::Read;
|
|
|
|
|
|
fn read_username_from_file() -> Result<String, io::Error> {
|
|
|
let mut s = String::new();
|
|
|
|
|
|
File::open("hello.txt")?.read_to_string(&mut s)?;
|
|
|
|
|
|
Ok(s)
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>瞧见没？ <code>?</code> 还能实现链式调用，<code>File::open</code> 遇到错误就返回，没有错误就将 <code>Ok</code> 中的值取出来用于下一个方法调用，简直太精妙了，从 Go 语言过来的我，内心狂喜（其实学 Rust 的苦和痛我才不会告诉你们）。</p>
|
|
|
<p>不仅有更强，还要有最强，我不信还有人比我更短(不要误解)：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>use std::fs;
|
|
|
use std::io;
|
|
|
|
|
|
fn read_username_from_file() -> Result<String, io::Error> {
|
|
|
// read_to_string是定义在std::io中的方法，因此需要在上面进行引用
|
|
|
fs::read_to_string("hello.txt")
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>从文件读取数据到字符串中，是比较常见的操作，因此 Rust 标准库为我们提供了 <code>fs::read_to_string</code> 函数，该函数内部会打开一个文件、创建 <code>String</code>、读取文件内容最后写入字符串并返回，因为该函数其实与本章讲的内容关系不大，因此放在最后来讲，其实只是我想震你们一下 :)</p>
|
|
|
<h4 id="-用于-option-的返回"><a class="header" href="#-用于-option-的返回">? 用于 Option 的返回</a></h4>
|
|
|
<p><code>?</code> 不仅仅可以用于 <code>Result</code> 的传播，还能用于 <code>Option</code> 的传播，再来回忆下 <code>Option</code> 的定义：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>pub enum Option<T> {
|
|
|
Some(T),
|
|
|
None
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p><code>Result</code> 通过 <code>?</code> 返回错误，那么 <code>Option</code> 就通过 <code>?</code> 返回 <code>None</code>：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>fn first(arr: &[i32]) -> Option<&i32> {
|
|
|
let v = arr.get(0)?;
|
|
|
Some(v)
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>上面的函数中，<code>arr.get</code> 返回一个 <code>Option<&i32></code> 类型，因为 <code>?</code> 的使用，如果 <code>get</code> 的结果是 <code>None</code>，则直接返回 <code>None</code>，如果是 <code>Some(&i32)</code>，则把里面的值赋给 <code>v</code>。</p>
|
|
|
<p>其实这个函数有些画蛇添足，我们完全可以写出更简单的版本：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>fn first(arr: &[i32]) -> Option<&i32> {
|
|
|
arr.get(0)
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>有一句话怎么说？没有需求，制造需求也要上……大家别跟我学习，这是软件开发大忌。只能用代码洗洗眼了：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>fn last_char_of_first_line(text: &str) -> Option<char> {
|
|
|
text.lines().next()?.chars().last()
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>上面代码展示了在链式调用中使用 <code>?</code> 提前返回 <code>None</code> 的用法， <code>.next</code> 方法返回的是 <code>Option</code> 类型：如果返回 <code>Some(&str)</code>，那么继续调用 <code>chars</code> 方法，如果返回 <code>None</code>，则直接从整个函数中返回 <code>None</code>，不再继续进行链式调用。</p>
|
|
|
<h4 id="新手用--常会犯的错误"><a class="header" href="#新手用--常会犯的错误">新手用 ? 常会犯的错误</a></h4>
|
|
|
<p>初学者在用 <code>?</code> 时，老是会犯错，例如写出这样的代码：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>fn first(arr: &[i32]) -> Option<&i32> {
|
|
|
arr.get(0)?
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>这段代码无法通过编译，切记：<code>?</code> 操作符需要一个变量来承载正确的值，这个函数只会返回 <code>Some(&i32)</code> 或者 <code>None</code>，只有错误值能直接返回，正确的值不行，所以如果数组中存在 0 号元素，那么函数第二行使用 <code>?</code> 后的返回类型为 <code>&i32</code> 而不是 <code>Some(&i32)</code>。因此 <code>?</code> 只能用于以下形式：</p>
|
|
|
<ul>
|
|
|
<li><code>let v = xxx()?;</code></li>
|
|
|
<li><code>xxx()?.yyy()?;</code></li>
|
|
|
</ul>
|
|
|
<h4 id="带返回值的-main-函数"><a class="header" href="#带返回值的-main-函数">带返回值的 main 函数</a></h4>
|
|
|
<p>在了解了 <code>?</code> 的使用限制后，这段代码你很容易看出它无法编译：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::fs::File;
|
|
|
|
|
|
fn main() {
|
|
|
let f = File::open("hello.txt")?;
|
|
|
}</code></pre></pre>
|
|
|
<p>运行后会报错:</p>
|
|
|
<pre><code class="language-shell">$ cargo run
|
|
|
...
|
|
|
the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
|
|
|
--> src/main.rs:4:48
|
|
|
|
|
|
|
3 | fn main() {
|
|
|
| --------- this function should return `Result` or `Option` to accept `?`
|
|
|
4 | let greeting_file = File::open("hello.txt")?;
|
|
|
| ^ cannot use the `?` operator in a function that returns `()`
|
|
|
|
|
|
|
= help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
|
|
|
</code></pre>
|
|
|
<p>因为 <code>?</code> 要求 <code>Result<T, E></code> 形式的返回值，而 <code>main</code> 函数的返回是 <code>()</code>，因此无法满足，那是不是就无解了呢？</p>
|
|
|
<p>实际上 Rust 还支持另外一种形式的 <code>main</code> 函数：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">use std::error::Error;
|
|
|
use std::fs::File;
|
|
|
|
|
|
fn main() -> Result<(), Box<dyn Error>> {
|
|
|
let f = File::open("hello.txt")?;
|
|
|
|
|
|
Ok(())
|
|
|
}</code></pre></pre>
|
|
|
<p>这样就能使用 <code>?</code> 提前返回了，同时我们又一次看到了<code>Box<dyn Error></code> 特征对象，因为 <code>std::error:Error</code> 是 Rust 中抽象层次最高的错误，其它标准库中的错误都实现了该特征，因此我们可以用该特征对象代表一切错误，就算 <code>main</code> 函数中调用任何标准库函数发生错误，都可以通过 <code>Box<dyn Error></code> 这个特征对象进行返回。</p>
|
|
|
<p>至于 <code>main</code> 函数可以有多种返回值，那是因为实现了 <a href="https://doc.rust-lang.org/std/process/trait.Termination.html">std::process::Termination</a> 特征，目前为止该特征还没进入稳定版 Rust 中，也许未来你可以为自己的类型实现该特征！</p>
|
|
|
<h4 id="try"><a class="header" href="#try">try!</a></h4>
|
|
|
<p>在 <code>?</code> 横空出世之前( Rust 1.13 )，Rust 开发者还可以使用 <code>try!</code> 来处理错误，该宏的大致定义如下：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>macro_rules! try {
|
|
|
($e:expr) => (match $e {
|
|
|
Ok(val) => val,
|
|
|
Err(err) => return Err(::std::convert::From::from(err)),
|
|
|
});
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>简单看一下与 <code>?</code> 的对比:</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>// `?`
|
|
|
let x = function_with_error()?; // 若返回 Err, 则立刻返回；若返回 Ok(255)，则将 x 的值设置为 255
|
|
|
|
|
|
// `try!()`
|
|
|
let x = try!(function_with_error());
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>可以看出 <code>?</code> 的优势非常明显，何况 <code>?</code> 还能做链式调用。</p>
|
|
|
<p>总之，<code>try!</code> 作为前浪已经死在了沙滩上，<strong>在当前版本中，我们要尽量避免使用 try!</strong>。</p>
|
|
|
<h2 id="课后练习"><a class="header" href="#课后练习">课后练习</a></h2>
|
|
|
<blockquote>
|
|
|
<p><a href="https://practice-zh.course.rs/result-panic/result.html">Rust By Practice</a>，支持代码在线编辑和运行，并提供详细的<a href="https://github.com/sunface/rust-by-practice/blob/master/solutions/result-panic/result.md">习题解答</a>。</p>
|
|
|
</blockquote>
|
|
|
|
|
|
<div id="giscus-container"></div>
|
|
|
</main>
|
|
|
|
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
|
|
<!-- Mobile navigation buttons -->
|
|
|
<a rel="prev" href="../../basic/result-error/panic.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
|
<i class="fa fa-angle-left"></i>
|
|
|
</a>
|
|
|
|
|
|
<a rel="next prefetch" href="../../basic/crate-module/intro.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
|
<i class="fa fa-angle-right"></i>
|
|
|
</a>
|
|
|
|
|
|
<div style="clear: both"></div>
|
|
|
</nav>
|
|
|
</div>
|
|
|
</div>
|
|
|
|
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
|
|
<a rel="prev" href="../../basic/result-error/panic.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
|
<i class="fa fa-angle-left"></i>
|
|
|
</a>
|
|
|
|
|
|
<a rel="next prefetch" href="../../basic/crate-module/intro.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
|
<i class="fa fa-angle-right"></i>
|
|
|
</a>
|
|
|
</nav>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<script>
|
|
|
window.playground_copyable = true;
|
|
|
</script>
|
|
|
|
|
|
<script src="../../ace.js"></script>
|
|
|
<script src="../../editor.js"></script>
|
|
|
<script src="../../mode-rust.js"></script>
|
|
|
<script src="../../theme-dawn.js"></script>
|
|
|
<script src="../../theme-tomorrow_night.js"></script>
|
|
|
|
|
|
<script src="../../elasticlunr.min.js"></script>
|
|
|
<script src="../../mark.min.js"></script>
|
|
|
<script src="../../searcher.js"></script>
|
|
|
|
|
|
<script src="../../clipboard.min.js"></script>
|
|
|
<script src="../../highlight.js"></script>
|
|
|
<script src="../../book.js"></script>
|
|
|
|
|
|
<script type="text/javascript" charset="utf-8">
|
|
|
var pagePath = "basic/result-error/result.md"
|
|
|
</script>
|
|
|
|
|
|
|
|
|
<!-- Custom JS scripts -->
|
|
|
<script src="../../assets/custom.js"></script>
|
|
|
<script src="../../assets/bigPicture.js"></script>
|
|
|
|
|
|
|
|
|
</div>
|
|
|
</body>
|
|
|
</html> |
