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<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="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 expanded "><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 expanded "><a href="../../basic/trait/advance-trait.html" class="active"><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 "><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 "><a href="../../basic/result-error/result.html"><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> &amp;'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、&amp;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/advanced-lists/intro.html"><strong aria-hidden="true">13.7.</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/unsafe-deque.html"><strong aria-hidden="true">13.7.1.</strong> 生产级可用的双向链表</a></li><li class="chapter-item "><a href="../../too-many-lists/advanced-lists/double-singly.html"><strong aria-hidden="true">13.7.2.</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">13.7.3.</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></ol></li></ol></li></ol>
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<main>
<h1 id="深入了解特征"><a class="header" href="#深入了解特征">深入了解特征</a></h1>
<p>特征之于 Rust 更甚于接口之于其他语言，因此特征在 Rust 中很重要也相对较为复杂，我们决定把特征分为两篇进行介绍，<a href="https://course.rs/basic/trait/trait.html">第一篇</a>在之前已经讲过，现在就是第二篇：关于特征的进阶篇，会讲述一些不常用到但是你该了解的特性。</p>
<h2 id="关联类型"><a class="header" href="#关联类型">关联类型</a></h2>
<p>在方法一章中，我们讲到了<a href="https://course.rs/basic/method#%E5%85%B3%E8%81%94%E5%87%BD%E6%95%B0">关联函数</a>，但是实际上关联类型和关联函数并没有任何交集，虽然它们的名字有一半的交集。</p>
<p>关联类型是在特征定义的语句块中，申明一个自定义类型，这样就可以在特征的方法签名中使用该类型：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub trait Iterator {
type Item;
fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt;;
}
<span class="boring">}
</span></code></pre></pre>
<p>以上是标准库中的迭代器特征 <code>Iterator</code>，它有一个 <code>Item</code> 关联类型，用于替代遍历的值的类型。</p>
<p>同时，<code>next</code> 方法也返回了一个 <code>Item</code> 类型，不过使用 <code>Option</code> 枚举进行了包裹，假如迭代器中的值是 <code>i32</code> 类型，那么调用 <code>next</code> 方法就将获取一个 <code>Option&lt;i32&gt;</code> 的值。</p>
<p>还记得 <code>Self</code> 吧？在之前的章节<a href="https://course.rs/basic/trait/trait-object#self-%E4%B8%8E-self">提到过</a>， <strong><code>Self</code> 用来指代当前调用者的具体类型，那么 <code>Self::Item</code> 就用来指代该类型实现中定义的 <code>Item</code> 类型</strong>：</p>
<pre><pre class="playground"><code class="language-rust edition2021">impl Iterator for Counter {
type Item = u32;
fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
// --snip--
}
}
fn main() {
let c = Counter{..}
c.next()
}
</code></pre></pre>
<p>在上述代码中，我们为 <code>Counter</code> 类型实现了 <code>Iterator</code> 特征，变量 <code>c</code> 是特征 <code>Iterator</code> 的实例，也是 <code>next</code> 方法的调用者。 结合之前的黑体内容可以得出：对于 <code>next</code> 方法而言，<code>Self</code> 是调用者 <code>c</code> 的具体类型： <code>Counter</code>，而 <code>Self::Item</code> 是 <code>Counter</code> 中定义的 <code>Item</code> 类型: <code>u32</code>。</p>
<p>聪明的读者之所以聪明，是因为你们喜欢联想和举一反三，同时你们也喜欢提问：为何不用泛型，例如如下代码：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub trait Iterator&lt;Item&gt; {
fn next(&amp;mut self) -&gt; Option&lt;Item&gt;;
}
<span class="boring">}
</span></code></pre></pre>
<p>答案其实很简单，为了代码的可读性，当你使用了泛型后，你需要在所有地方都写 <code>Iterator&lt;Item&gt;</code>，而使用了关联类型，你只需要写 <code>Iterator</code>，当类型定义复杂时，这种写法可以极大的增加可读性：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub trait CacheableItem: Clone + Default + fmt::Debug + Decodable + Encodable {
type Address: AsRef&lt;[u8]&gt; + Clone + fmt::Debug + Eq + Hash;
fn is_null(&amp;self) -&gt; bool;
}
<span class="boring">}
</span></code></pre></pre>
<p>例如上面的代码，<code>Address</code> 的写法自然远比 <code>AsRef&lt;[u8]&gt; + Clone + fmt::Debug + Eq + Hash</code> 要简单的多，而且含义清晰。</p>
<p>再例如，如果使用泛型，你将得到以下的代码：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>trait Container&lt;A,B&gt; {
fn contains(&amp;self,a: A,b: B) -&gt; bool;
}
fn difference&lt;A,B,C&gt;(container: &amp;C) -&gt; i32
where
C : Container&lt;A,B&gt; {...}
<span class="boring">}
</span></code></pre></pre>
<p>可以看到，由于使用了泛型，导致函数头部也必须增加泛型的声明，而使用关联类型，将得到可读性好得多的代码：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>trait Container{
type A;
type B;
fn contains(&amp;self, a: &amp;Self::A, b: &amp;Self::B) -&gt; bool;
}
fn difference&lt;C: Container&gt;(container: &amp;C) {}
<span class="boring">}
</span></code></pre></pre>
<h2 id="默认泛型类型参数"><a class="header" href="#默认泛型类型参数">默认泛型类型参数</a></h2>
<p>当使用泛型类型参数时，可以为其指定一个默认的具体类型，例如标准库中的 <code>std::ops::Add</code> 特征：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>trait Add&lt;RHS=Self&gt; {
type Output;
fn add(self, rhs: RHS) -&gt; Self::Output;
}
<span class="boring">}
</span></code></pre></pre>
<p>它有一个泛型参数 <code>RHS</code>，但是与我们以往的用法不同，这里它给 <code>RHS</code> 一个默认值，也就是当用户不指定 <code>RHS</code> 时，默认使用两个同样类型的值进行相加，然后返回一个关联类型 <code>Output</code>。</p>
<p>可能上面那段不太好理解，下面我们用代码来举例：</p>
<pre><pre class="playground"><code class="language-rust edition2021">use std::ops::Add;
#[derive(Debug, PartialEq)]
struct Point {
x: i32,
y: i32,
}
impl Add for Point {
type Output = Point;
fn add(self, other: Point) -&gt; Point {
Point {
x: self.x + other.x,
y: self.y + other.y,
}
}
}
fn main() {
assert_eq!(Point { x: 1, y: 0 } + Point { x: 2, y: 3 },
Point { x: 3, y: 3 });
}
</code></pre></pre>
<p>上面的代码主要干了一件事，就是为 <code>Point</code> 结构体提供 <code>+</code> 的能力，这就是<strong>运算符重载</strong>，不过 Rust 并不支持创建自定义运算符，你也无法为所有运算符进行重载，目前来说，只有定义在 <code>std::ops</code> 中的运算符才能进行重载。</p>
<p>跟 <code>+</code> 对应的特征是 <code>std::ops::Add</code>，我们在之前也看过它的定义 <code>trait Add&lt;RHS=Self&gt;</code>，但是上面的例子中并没有为 <code>Point</code> 实现 <code>Add&lt;RHS&gt;</code> 特征，而是实现了 <code>Add</code> 特征（没有默认泛型类型参数），这意味着我们使用了 <code>RHS</code> 的默认类型，也就是 <code>Self</code>。换句话说，我们这里定义的是两个相同的 <code>Point</code> 类型相加，因此无需指定 <code>RHS</code>。</p>
<p>与上面的例子相反，下面的例子，我们来创建两个不同类型的相加：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::ops::Add;
struct Millimeters(u32);
struct Meters(u32);
impl Add&lt;Meters&gt; for Millimeters {
type Output = Millimeters;
fn add(self, other: Meters) -&gt; Millimeters {
Millimeters(self.0 + (other.0 * 1000))
}
}
<span class="boring">}
</span></code></pre></pre>
<p>这里，是进行 <code>Millimeters + Meters</code> 两种数据类型的 <code>+</code> 操作，因此此时不能再使用默认的 <code>RHS</code>，否则就会变成 <code>Millimeters + Millimeters</code> 的形式。使用 <code>Add&lt;Meters&gt;</code> 可以将 <code>RHS</code> 指定为 <code>Meters</code>，那么 <code>fn add(self, rhs: RHS)</code> 自然而言的变成了 <code>Millimeters</code> 和 <code>Meters</code> 的相加。</p>
<p>默认类型参数主要用于两个方面：</p>
<ol>
<li>减少实现的样板代码</li>
<li>扩展类型但是无需大幅修改现有的代码</li>
</ol>
<p>之前的例子就是第一点，虽然效果也就那样。在 <code>+</code> 左右两边都是同样类型时，只需要 <code>impl Add</code> 即可，否则你需要 <code>impl Add&lt;SOME_TYPE&gt;</code>，嗯，会多写几个字:)</p>
<p>对于第二点，也很好理解，如果你在一个复杂类型的基础上，新引入一个泛型参数，可能需要修改很多地方，但是如果新引入的泛型参数有了默认类型，情况就会好很多，添加泛型参数后，使用这个类型的代码需要逐个在类型提示部分添加泛型参数，就很麻烦；但是有了默认参数（且默认参数取之前的实现里假设的值的情况下）之后，原有的使用这个类型的代码就不需要做改动了。</p>
<p>归根到底，默认泛型参数，是有用的，但是大多数情况下，咱们确实用不到，当需要用到时，大家再回头来查阅本章即可，<strong>手上有剑，心中不慌</strong>。</p>
<h2 id="调用同名的方法"><a class="header" href="#调用同名的方法">调用同名的方法</a></h2>
<p>不同特征拥有同名的方法是很正常的事情，你没有任何办法阻止这一点；甚至除了特征上的同名方法外，在你的类型上，也有同名方法：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>trait Pilot {
fn fly(&amp;self);
}
trait Wizard {
fn fly(&amp;self);
}
struct Human;
impl Pilot for Human {
fn fly(&amp;self) {
println!(&quot;This is your captain speaking.&quot;);
}
}
impl Wizard for Human {
fn fly(&amp;self) {
println!(&quot;Up!&quot;);
}
}
impl Human {
fn fly(&amp;self) {
println!(&quot;*waving arms furiously*&quot;);
}
}
<span class="boring">}
</span></code></pre></pre>
<p>这里，不仅仅两个特征 <code>Pilot</code> 和 <code>Wizard</code> 有 <code>fly</code> 方法，就连实现那两个特征的 <code>Human</code> 单元结构体，也拥有一个同名方法 <code>fly</code> (这世界怎么了，非要这么卷吗？程序员何苦难为程序员，哎)。</p>
<p>既然代码已经不可更改，那下面我们来讲讲该如何调用这些 <code>fly</code> 方法。</p>
<h4 id="优先调用类型上的方法"><a class="header" href="#优先调用类型上的方法">优先调用类型上的方法</a></h4>
<p>当调用 <code>Human</code> 实例的 <code>fly</code> 时，编译器默认调用该类型中定义的方法：</p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let person = Human;
person.fly();
}
</code></pre></pre>
<p>这段代码会打印 <code>*waving arms furiously*</code>，说明直接调用了类型上定义的方法。</p>
<h4 id="调用特征上的方法"><a class="header" href="#调用特征上的方法">调用特征上的方法</a></h4>
<p>为了能够调用两个特征的方法，需要使用显式调用的语法：</p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let person = Human;
Pilot::fly(&amp;person); // 调用Pilot特征上的方法
Wizard::fly(&amp;person); // 调用Wizard特征上的方法
person.fly(); // 调用Human类型自身的方法
}
</code></pre></pre>
<p>运行后依次输出：</p>
<pre><code class="language-console">This is your captain speaking.
Up!
*waving arms furiously*
</code></pre>
<p>因为 <code>fly</code> 方法的参数是 <code>self</code>，当显式调用时，编译器就可以根据调用的类型( <code>self</code> 的类型)决定具体调用哪个方法。</p>
<p>这个时候问题又来了，如果方法没有 <code>self</code> 参数呢？稍等，估计有读者会问：还有方法没有 <code>self</code> 参数？看到这个疑问，作者的眼泪不禁流了下来，大明湖畔的<a href="https://course.rs/basic/method.html#%E5%85%B3%E8%81%94%E5%87%BD%E6%95%B0">关联函数</a>，你还记得嘛？</p>
<p>但是成年人的世界，就算再伤心，事还得做，咱们继续：</p>
<pre><pre class="playground"><code class="language-rust edition2021">trait Animal {
fn baby_name() -&gt; String;
}
struct Dog;
impl Dog {
fn baby_name() -&gt; String {
String::from(&quot;Spot&quot;)
}
}
impl Animal for Dog {
fn baby_name() -&gt; String {
String::from(&quot;puppy&quot;)
}
}
fn main() {
println!(&quot;A baby dog is called a {}&quot;, Dog::baby_name());
}
</code></pre></pre>
<p>就像人类妈妈会给自己的宝宝起爱称一样，狗妈妈也会。狗妈妈称呼自己的宝宝为<strong>Spot</strong>，其它动物称呼狗宝宝为<strong>puppy</strong>，这个时候假如有动物不知道该如何称呼狗宝宝，它需要查询一下。</p>
<p><code>Dog::baby_name()</code> 的调用方式显然不行，因为这只是狗妈妈对宝宝的爱称，可能你会想到通过下面的方式查询其他动物对狗狗的称呼：</p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
println!(&quot;A baby dog is called a {}&quot;, Animal::baby_name());
}
</code></pre></pre>
<p>铛铛，无情报错了：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>error[E0283]: type annotations needed // 需要类型注释
--&gt; src/main.rs:20:43
|
20 | println!(&quot;A baby dog is called a {}&quot;, Animal::baby_name());
| ^^^^^^^^^^^^^^^^^ cannot infer type // 无法推断类型
|
= note: cannot satisfy `_: Animal`
<span class="boring">}
</span></code></pre></pre>
<p>因为单纯从 <code>Animal::baby_name()</code> 上，编译器无法得到任何有效的信息：实现 <code>Animal</code> 特征的类型可能有很多，你究竟是想获取哪个动物宝宝的名称？狗宝宝？猪宝宝？还是熊宝宝？</p>
<p>此时，就需要使用<strong>完全限定语法</strong>。</p>
<h5 id="完全限定语法"><a class="header" href="#完全限定语法">完全限定语法</a></h5>
<p>完全限定语法是调用函数最为明确的方式：</p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
println!(&quot;A baby dog is called a {}&quot;, &lt;Dog as Animal&gt;::baby_name());
}
</code></pre></pre>
<p>在尖括号中，通过 <code>as</code> 关键字，我们向 Rust 编译器提供了类型注解，也就是 <code>Animal</code> 就是 <code>Dog</code>，而不是其他动物，因此最终会调用 <code>impl Animal for Dog</code> 中的方法，获取到其它动物对狗宝宝的称呼：<strong>puppy</strong>。</p>
<p>言归正题，完全限定语法定义为：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>&lt;Type as Trait&gt;::function(receiver_if_method, next_arg, ...);
<span class="boring">}
</span></code></pre></pre>
<p>上面定义中，第一个参数是方法接收器 <code>receiver</code> （三种 <code>self</code>），只有方法才拥有，例如关联函数就没有 <code>receiver</code>。</p>
<p>完全限定语法可以用于任何函数或方法调用，那么我们为何很少用到这个语法？原因是 Rust 编译器能根据上下文自动推导出调用的路径，因此大多数时候，我们都无需使用完全限定语法。只有当存在多个同名函数或方法，且 Rust 无法区分出你想调用的目标函数时，该用法才能真正有用武之地。</p>
<h2 id="特征定义中的特征约束"><a class="header" href="#特征定义中的特征约束">特征定义中的特征约束</a></h2>
<p>有时，我们会需要让某个特征 A 能使用另一个特征 B 的功能(另一种形式的特征约束)，这种情况下，不仅仅要为类型实现特征 A，还要为类型实现特征 B 才行，这就是 <code>supertrait</code> (实在不知道该如何翻译，有大佬指导下嘛？)</p>
<p>例如有一个特征 <code>OutlinePrint</code>，它有一个方法，能够对当前的实现类型进行格式化输出：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::fmt::Display;
trait OutlinePrint: Display {
fn outline_print(&amp;self) {
let output = self.to_string();
let len = output.len();
println!(&quot;{}&quot;, &quot;*&quot;.repeat(len + 4));
println!(&quot;*{}*&quot;, &quot; &quot;.repeat(len + 2));
println!(&quot;* {} *&quot;, output);
println!(&quot;*{}*&quot;, &quot; &quot;.repeat(len + 2));
println!(&quot;{}&quot;, &quot;*&quot;.repeat(len + 4));
}
}
<span class="boring">}
</span></code></pre></pre>
<p>等等，这里有一个眼熟的语法: <code>OutlinePrint: Display</code>，感觉很像之前讲过的<strong>特征约束</strong>，只不过用在了特征定义中而不是函数的参数中，是的，在某种意义上来说，这和特征约束非常类似，都用来说明一个特征需要实现另一个特征，这里就是：如果你想要实现 <code>OutlinePrint</code> 特征，首先你需要实现 <code>Display</code> 特征。</p>
<p>想象一下，假如没有这个特征约束，那么 <code>self.to_string</code> 还能够调用吗（ <code>to_string</code> 方法会为实现 <code>Display</code> 特征的类型自动实现）？编译器肯定是不愿意的，会报错说当前作用域中找不到用于 <code>&amp;Self</code> 类型的方法 <code>to_string</code> ：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>struct Point {
x: i32,
y: i32,
}
impl OutlinePrint for Point {}
<span class="boring">}
</span></code></pre></pre>
<p>因为 <code>Point</code> 没有实现 <code>Display</code> 特征，会得到下面的报错：</p>
<pre><code class="language-console">error[E0277]: the trait bound `Point: std::fmt::Display` is not satisfied
--&gt; src/main.rs:20:6
|
20 | impl OutlinePrint for Point {}
| ^^^^^^^^^^^^ `Point` cannot be formatted with the default formatter;
try using `:?` instead if you are using a format string
|
= help: the trait `std::fmt::Display` is not implemented for `Point`
</code></pre>
<p>既然我们有求于编译器，那只能选择满足它咯：</p>
<pre><pre class="playground"><code class="language-rust edition2021">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::fmt;
impl fmt::Display for Point {
fn fmt(&amp;self, f: &amp;mut fmt::Formatter) -&gt; fmt::Result {
write!(f, &quot;({}, {})&quot;, self.x, self.y)
}
}
<span class="boring">}
</span></code></pre></pre>
<p>上面代码为 <code>Point</code> 实现了 <code>Display</code> 特征，那么 <code>to_string</code> 方法也将自动实现：最终获得字符串是通过这里的 <code>fmt</code> 方法获得的。</p>
<h2 id="在外部类型上实现外部特征newtype"><a class="header" href="#在外部类型上实现外部特征newtype">在外部类型上实现外部特征(newtype)</a></h2>
<p>在<a href="https://course.rs/basic/trait/trait#%E7%89%B9%E5%BE%81%E5%AE%9A%E4%B9%89%E4%B8%8E%E5%AE%9E%E7%8E%B0%E7%9A%84%E4%BD%8D%E7%BD%AE%E5%AD%A4%E5%84%BF%E8%A7%84%E5%88%99">特征</a>章节中，有提到孤儿规则，简单来说，就是特征或者类型必需至少有一个是本地的，才能在此类型上定义特征。</p>
<p>这里提供一个办法来绕过孤儿规则，那就是使用<strong>newtype 模式</strong>，简而言之：就是为一个<a href="https://course.rs/basic/compound-type/struct#%E5%85%83%E7%BB%84%E7%BB%93%E6%9E%84%E4%BD%93tuple-struct">元组结构体</a>创建新类型。该元组结构体封装有一个字段，该字段就是希望实现特征的具体类型。</p>
<p>该封装类型是本地的，因此我们可以为此类型实现外部的特征。</p>
<p><code>newtype</code> 不仅仅能实现以上的功能，而且它在运行时没有任何性能损耗，因为在编译期，该类型会被自动忽略。</p>
<p>下面来看一个例子，我们有一个动态数组类型： <code>Vec&lt;T&gt;</code>，它定义在标准库中，还有一个特征 <code>Display</code>，它也定义在标准库中，如果没有 <code>newtype</code>，我们是无法为 <code>Vec&lt;T&gt;</code> 实现 <code>Display</code> 的：</p>
<pre><code class="language-console">error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
--&gt; src/main.rs:5:1
|
5 | impl&lt;T&gt; std::fmt::Display for Vec&lt;T&gt; {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^------
| | |
| | Vec is not defined in the current crate
| impl doesn't use only types from inside the current crate
|
= note: define and implement a trait or new type instead
</code></pre>
<p>编译器给了我们提示： <code>define and implement a trait or new type instead</code>，重新定义一个特征，或者使用 <code>new type</code>，前者当然不可行，那么来试试后者：</p>
<pre><pre class="playground"><code class="language-rust edition2021">use std::fmt;
struct Wrapper(Vec&lt;String&gt;);
impl fmt::Display for Wrapper {
fn fmt(&amp;self, f: &amp;mut fmt::Formatter) -&gt; fmt::Result {
write!(f, &quot;[{}]&quot;, self.0.join(&quot;, &quot;))
}
}
fn main() {
let w = Wrapper(vec![String::from(&quot;hello&quot;), String::from(&quot;world&quot;)]);
println!(&quot;w = {}&quot;, w);
}
</code></pre></pre>
<p>其中，<code>struct Wrapper(Vec&lt;String&gt;)</code> 就是一个元组结构体，它定义了一个新类型 <code>Wrapper</code>，代码很简单，相信大家也很容易看懂。</p>
<p>既然 <code>new type</code> 有这么多好处，它有没有不好的地方呢？答案是肯定的。注意到我们怎么访问里面的数组吗？<code>self.0.join(&quot;, &quot;)</code>，是的，很啰嗦，因为需要先从 <code>Wrapper</code> 中取出数组: <code>self.0</code>，然后才能执行 <code>join</code> 方法。</p>
<p>类似的，任何数组上的方法，你都无法直接调用，需要先用 <code>self.0</code> 取出数组，然后再进行调用。</p>
<p>当然，解决办法还是有的，要不怎么说 Rust 是极其强大灵活的编程语言！Rust 提供了一个特征叫 <a href="https://course.rs/advance/smart-pointer/deref.html"><code>Deref</code></a>，实现该特征后，可以自动做一层类似类型转换的操作，可以将 <code>Wrapper</code> 变成 <code>Vec&lt;String&gt;</code> 来使用。这样就会像直接使用数组那样去使用 <code>Wrapper</code>，而无需为每一个操作都添加上 <code>self.0</code>。</p>
<p>同时，如果不想 <code>Wrapper</code> 暴露底层数组的所有方法，我们还可以为 <code>Wrapper</code> 去重载这些方法，实现隐藏的目的。</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://zh.practice.rs/generics-traits/advanced-traits.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/generics-traits/advanced-trait.md">习题解答</a>。</p>
</blockquote>
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