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< h1 id = "注释和文档" > < a class = "header" href = "#注释和文档" > 注释和文档< / a > < / h1 >
< p > 好的代码会说话，好的程序员不写注释，这些都是烂大街的“编程界俚语”。但是，如果你真的遇到一个不写注释的项目或程序员，那一定会对它/他“刮目相看”。< / p >
< p > 在之前的章节我们学习了包和模块如何使用，在此章节将进一步学习如何书写文档注释，以及如何使用 < code > cargo doc< / code > 生成项目的文档，最后将以一个包、模块和文档的综合性例子，来将这些知识融会贯通。< / p >
< h2 id = "注释的种类" > < a class = "header" href = "#注释的种类" > 注释的种类< / a > < / h2 >
< p > 在 Rust 中，注释分为三类：< / p >
< ul >
< li > 代码注释，用于说明某一块代码的功能，读者往往是同一个项目的协作开发者< / li >
< li > 文档注释，支持 < code > Markdown< / code > ，对项目描述、公共 API 等用户关心的功能进行介绍，同时还能提供示例代码，目标读者往往是想要了解你项目的人< / li >
< li > 包和模块注释，严格来说这也是文档注释中的一种，它主要用于说明当前包和模块的功能，方便用户迅速了解一个项目< / li >
< / ul >
< p > 通过这些注释，实现了 Rust 极其优秀的文档化支持，甚至你还能在文档注释中写测试用例，省去了单独写测试用例的环节，我直呼好家伙！< / p >
< h2 id = "代码注释" > < a class = "header" href = "#代码注释" > 代码注释< / a > < / h2 >
< p > 显然之前的刮目相看是打了引号的，想要去掉引号，该写注释的时候，就老老实实的，不过写时需要遵循八字原则：< strong > 围绕目标，言简意赅< / strong > ，记住，洋洋洒洒那是用来形容文章的，不是形容注释！< / p >
< p > 代码注释方式有两种：< / p >
< h4 id = "行注释-" > < a class = "header" href = "#行注释-" > 行注释 < code > //< / code > < / a > < / h4 >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
// 我是Sun...
// face
let name = "sunface";
let age = 18; // 今年好像是18岁
}< / code > < / pre >
< p > 如上所示，行注释可以放在某一行代码的上方，也可以放在当前代码行的后方。如果超出一行的长度，需要在新行的开头也加上 < code > //< / code > 。< / p >
< p > 当注释行数较多时，你还可以使用< strong > 块注释< / strong > < / p >
< h4 id = "块注释--" > < a class = "header" href = "#块注释--" > 块注释< code > /* ..... */< / code > < / a > < / h4 >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
/*
我
是
S
u
n
... 哎，好长!
*/
let name = "sunface";
let age = "???"; // 今年其实。。。挺大了
}< / code > < / pre >
< p > 如上所示，只需要将注释内容使用 < code > /* */< / code > 进行包裹即可。< / p >
< p > 你会发现， < / p >
< h2 id = "文档注释" > < a class = "header" href = "#文档注释" > 文档注释< / a > < / h2 >
< p > 当查看一个 < code > crates.io< / code > 上的包时，往往需要通过它提供的文档来浏览相关的功能特性、使用方式，这种文档就是通过文档注释实现的。< / p >
< p > Rust 提供了 < code > cargo doc< / code > 的命令，可以用于把这些文档注释转换成 < code > HTML< / code > 网页文件，最终展示给用户浏览，这样用户就知道这个包是做什么的以及该如何使用。< / p >
< h4 id = "文档行注释-" > < a class = "header" href = "#文档行注释-" > 文档行注释 < code > ///< / code > < / a > < / h4 >
< p > 本书的一大特点就是废话不多，因此我们开门见山：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /// `add_one` 将指定值加1
///
/// # Examples
///
/// ```
/// let arg = 5;
/// let answer = my_crate::add_one(arg);
///
/// assert_eq!(6, answer);
/// ```
pub fn add_one(x: i32) -> i32 {
x + 1
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 以上代码有几点需要注意：< / p >
< ul >
< li > 文档注释需要位于 < code > lib< / code > 类型的包中，例如 < code > src/lib.rs< / code > 中< / li >
< li > 文档注释可以使用 < code > markdown< / code > 语法！例如 < code > # Examples< / code > 的标题，以及代码块高亮< / li >
< li > 被注释的对象需要使用 < code > pub< / code > 对外可见，记住：文档注释是给用户看的，< strong > 内部实现细节不应该被暴露出去< / strong > < / li >
< / ul >
< p > 咦？文档注释中的例子，为什看上去像是能运行的样子？竟然还是有 < code > assert_eq< / code > 这种常用于测试目的的宏。 嗯，你的感觉没错，详细内容会在本章后面讲解，容我先卖个关子。< / p >
< h4 id = "文档块注释---" > < a class = "header" href = "#文档块注释---" > 文档块注释 < code > /** ... */< / code > < / a > < / h4 >
< p > 与代码注释一样，文档也有块注释，当注释内容多时，使用块注释可以减少 < code > ///< / code > 的使用：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /** `add_two` 将指定值加2
< span class = "boring" > Examples
< / span >
```
let arg = 5;
let answer = my_crate::add_two(arg);
assert_eq!(7, answer);
```
*/
pub fn add_two(x: i32) -> i32 {
x + 2
}
< span class = "boring" > }< / span > < / code > < / pre >
< h4 id = "查看文档-cargo-doc" > < a class = "header" href = "#查看文档-cargo-doc" > 查看文档 cargo doc< / a > < / h4 >
< p > 锦衣不夜行，这是中国人的传统美德。我们写了这么漂亮的文档注释，当然要看看网页中是什么效果咯。< / p >
< p > 很简单，运行 < code > cargo doc< / code > 可以直接生成 < code > HTML< / code > 文件，放入< em > target/doc< / em > 目录下。< / p >
< p > 当然，为了方便，我们使用 < code > cargo doc --open< / code > 命令，可以在生成文档后，自动在浏览器中打开网页，最终效果如图所示：< / p >
< img alt = "" src = "https://pic2.zhimg.com/80/v2-926c91d429e2933a6a3ae3233fc56b1c_1440w.png" class = "center" / >
< p > 非常棒，而且非常简单，这就是 Rust 工具链的强大之处。< / p >
< h4 id = "常用文档标题" > < a class = "header" href = "#常用文档标题" > 常用文档标题< / a > < / h4 >
< p > 之前我们见到了在文档注释中该如何使用 < code > markdown< / code > ，其中包括 < code > # Examples< / code > 标题。除了这个标题，还有一些常用的，你可以在项目中酌情使用：< / p >
< ul >
< li > < strong > Panics< / strong > ：函数可能会出现的异常状况，这样调用函数的人就可以提前规避< / li >
< li > < strong > Errors< / strong > ：描述可能出现的错误及什么情况会导致错误，有助于调用者针对不同的错误采取不同的处理方式< / li >
< li > < strong > Safety< / strong > ：如果函数使用 < code > unsafe< / code > 代码，那么调用者就需要注意一些使用条件，以确保 < code > unsafe< / code > 代码块的正常工作< / li >
< / ul >
< p > 话说回来，这些标题更多的是一种惯例，如果你非要用中文标题也没问题，但是最好在团队中保持同样的风格 :)< / p >
< h2 id = "包和模块级别的注释" > < a class = "header" href = "#包和模块级别的注释" > 包和模块级别的注释< / a > < / h2 >
< p > 除了函数、结构体等 Rust 项的注释，你还可以给包和模块添加注释，需要注意的是，< strong > 这些注释要添加到包、模块的最上方< / strong > ！ < / p >
< p > 与之前的任何注释一样，包级别的注释也分为两种：行注释 < code > //!< / code > 和块注释 < code > /*! ... */< / code > 。< / p >
< p > 现在，为我们的包增加注释，在 < code > src/lib.rs< / code > 包根的最上方，添加：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /*! lib包是world_hello二进制包的依赖包，
里面包含了compute等有用模块 */
pub mod compute;
< span class = "boring" > }< / span > < / code > < / pre >
< p > 然后再为该包根的子模块 < code > src/compute.rs< / code > 添加注释：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > //! 计算一些你口算算不出来的复杂算术题
/// `add_one`将指定值加1
///
< span class = "boring" > }< / span > < / code > < / pre >
< p > 运行 < code > cargo doc --open< / code > 查看下效果：< / p >
< img alt = "" src = "https://pic3.zhimg.com/80/v2-38dbea938884c159e74f777c6f49e3af_1440w.png" class = "center" / >
< p > 包模块注释，可以让用户从整体的角度理解包的用途，对于用户来说是非常友好的，就和一篇文章的开头一样，总是要对文章的内容进行大致的介绍，让用户在看的时候心中有数。< / p >
< p > 至此，关于如何注释的内容，就结束了，那么注释还能用来做什么？可以玩出花来吗？答案是< code > Yes< / code > .< / p >
< h2 id = "文档测试doc-test" > < a class = "header" href = "#文档测试doc-test" > 文档测试(Doc Test)< / a > < / h2 >
< p > 相信读者之前都写过单元测试用例，其中一个很蛋疼的问题就是，随着代码的进化，单元测试用例经常会失效，过段时间后（为何是过段时间？应该这么问，有几个开发喜欢写测试用例 =,=），你发现需要连续修改不少处代码，才能让测试重新工作起来。然而，在 Rust 中，大可不必。< / p >
< p > 在之前的 < code > add_one< / code > 中，我们写的示例代码非常像是一个单元测试的用例，这是偶然吗？并不是。因为 Rust 允许我们在文档注释中写单元测试用例！方法就如同之前做的：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /// `add_one` 将指定值加1
///
/// # Examples11
///
/// ```
/// let arg = 5;
/// let answer = world_hello::compute::add_one(arg);
///
/// assert_eq!(6, answer);
/// ```
pub fn add_one(x: i32) -> i32 {
x + 1
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 以上的注释不仅仅是文档，还可以作为单元测试的用例运行，使用 < code > cargo test< / code > 运行测试：< / p >
< pre > < code class = "language-console" > Doc-tests world_hello
running 2 tests
test src/compute.rs - compute::add_one (line 8) ... ok
test src/compute.rs - compute::add_two (line 22) ... ok
test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.00s
< / code > < / pre >
< p > 可以看到，文档中的测试用例被完美运行，而且输出中也明确提示了 < code > Doc-tests world_hello< / code > ，意味着这些测试的名字叫 < code > Doc test< / code > 文档测试。< / p >
< blockquote >
< p > 需要注意的是，你可能需要使用类如 < code > world_hello::compute::add_one(arg)< / code > 的完整路径来调用函数，因为测试是在另外一个独立的线程中运行的< / p >
< / blockquote >
< h4 id = "造成-panic-的文档测试" > < a class = "header" href = "#造成-panic-的文档测试" > 造成 panic 的文档测试< / a > < / h4 >
< p > 文档测试中的用例还可以造成 < code > panic< / code > ： < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /// # Panics
///
/// The function panics if the second argument is zero.
///
/// ```rust
/// // panics on division by zero
/// world_hello::compute::div(10, 0);
/// ```
pub fn div(a: i32, b: i32) -> i32 {
if b == 0 {
panic!("Divide-by-zero error");
}
a / b
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 以上测试运行后会 < code > panic< / code > ： < / p >
< pre > < code class = "language-console" > ---- src/compute.rs - compute::div (line 38) stdout ----
Test executable failed (exit code 101).
stderr:
thread 'main' panicked at 'Divide-by-zero error', src/compute.rs:44:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
< / code > < / pre >
< p > 如果想要通过这种测试，可以添加 < code > should_panic< / code > ： < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /// # Panics
///
/// The function panics if the second argument is zero.
///
/// ```rust,should_panic
/// // panics on division by zero
/// world_hello::compute::div(10, 0);
/// ```
< span class = "boring" > }< / span > < / code > < / pre >
< p > 通过 < code > should_panic< / code > ，告诉 Rust 我们这个用例会导致 < code > panic< / code > ，这样测试用例就能顺利通过。< / p >
< h4 id = "保留测试隐藏文档" > < a class = "header" href = "#保留测试隐藏文档" > 保留测试，隐藏文档< / a > < / h4 >
< p > 在某些时候，我们希望保留文档测试的功能，但是又要将某些测试用例的内容从文档中隐藏起来：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > /// ```
/// # // 使用#开头的行会在文档中被隐藏起来，但是依然会在文档测试中运行
/// # fn try_main() -> Result< (), String> {
/// let res = world_hello::compute::try_div(10, 0)?;
/// # Ok(()) // returning from try_main
/// # }
/// # fn main() {
/// # try_main().unwrap();
/// #
/// # }
/// ```
pub fn try_div(a: i32, b: i32) -> Result< i32, String> {
if b == 0 {
Err(String::from("Divide-by-zero"))
} else {
Ok(a / b)
}
}< / code > < / pre >
< p > 以上文档注释中，我们使用 < code > #< / code > 将不想让用户看到的内容隐藏起来，但是又不影响测试用例的运行，最终用户将只能看到那行没有隐藏的 < code > let res = world_hello::compute::try_div(10, 0)?;< / code > ： < / p >
< img alt = "" src = "https://pic1.zhimg.com/80/v2-d1b98f5e70b7f8c8fb9aecce325dba0e_1440w.png" class = "center" / >
< h2 id = "文档注释中的代码跳转" > < a class = "header" href = "#文档注释中的代码跳转" > 文档注释中的代码跳转< / a > < / h2 >
< p > Rust 在文档注释中还提供了一个非常强大的功能，那就是可以实现对外部项的链接：< / p >
< h4 id = "跳转到标准库" > < a class = "header" href = "#跳转到标准库" > 跳转到标准库< / a > < / h4 >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /// `add_one` 返回一个[`Option`]类型
pub fn add_one(x: i32) -> Option< i32> {
Some(x + 1)
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 此处的 < strong > [< code > Option< / code > ]< / strong > 就是一个链接，指向了标准库中的 < code > Option< / code > 枚举类型，有两种方式可以进行跳转:< / p >
< ul >
< li > 在 IDE 中，使用 < code > Command + 鼠标左键< / code > (macOS)， < code > CTRL + 鼠标左键< / code > (Windows)< / li >
< li > 在文档中直接点击链接< / li >
< / ul >
< p > 再比如，还可以使用路径的方式跳转：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use std::sync::mpsc::Receiver;
/// [`Receiver< T> `] [`std::future`].
///
/// [`std::future::Future`] [`Self::recv()`].
pub struct AsyncReceiver< T> {
sender: Receiver< T> ,
}
impl< T> AsyncReceiver< T> {
pub async fn recv() -> T {
unimplemented!()
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< h4 id = "使用完整路径跳转到指定项" > < a class = "header" href = "#使用完整路径跳转到指定项" > 使用完整路径跳转到指定项< / a > < / h4 >
< p > 除了跳转到标准库，你还可以通过指定具体的路径跳转到自己代码或者其它库的指定项，例如在 < code > lib.rs< / code > 中添加以下代码：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub mod a {
/// `add_one` 返回一个[`Option`]类型
/// 跳转到[`crate::MySpecialFormatter`]
pub fn add_one(x: i32) -> Option< i32> {
Some(x + 1)
}
}
pub struct MySpecialFormatter;
< span class = "boring" > }< / span > < / code > < / pre >
< p > 使用 < code > crate::MySpecialFormatter< / code > 这种路径就可以实现跳转到 < code > lib.rs< / code > 中定义的结构体上。< / p >
< h4 id = "同名项的跳转" > < a class = "header" href = "#同名项的跳转" > 同名项的跳转< / a > < / h4 >
< p > 如果遇到同名项，可以使用标示类型的方式进行跳转：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > /// 跳转到结构体 [`Foo`](struct@Foo)
pub struct Bar;
/// 跳转到同名函数 [`Foo`](fn@Foo)
pub struct Foo {}
/// 跳转到同名宏 [`foo!`]
pub fn Foo() {}
#[macro_export]
macro_rules! foo {
() => {}
}
< span class = "boring" > }< / span > < / code > < / pre >
< h2 id = "文档搜索别名" > < a class = "header" href = "#文档搜索别名" > 文档搜索别名< / a > < / h2 >
< p > Rust 文档支持搜索功能，我们可以为自己的类型定义几个别名，以实现更好的搜索展现，当别名命中时，搜索结果会被放在第一位：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > #[doc(alias = "x")]
#[doc(alias = "big")]
pub struct BigX;
#[doc(alias("y", "big"))]
pub struct BigY;
< span class = "boring" > }< / span > < / code > < / pre >
< p > 结果如下图所示：
< img alt = "" src = "https://pic1.zhimg.com/80/v2-1ab5b19d2bd06f3d83204d062b399bcd_1440w.png" class = "center" / > < / p >
< h2 id = "一个综合例子" > < a class = "header" href = "#一个综合例子" > 一个综合例子< / a > < / h2 >
< p > 这个例子我们将重点应用几个知识点：< / p >
< ul >
< li > 文档注释< / li >
< li > 一个项目可以包含两个包：二进制可执行包和 < code > lib< / code > 包（库包），它们的包根分别是 < code > src/main.rs< / code > 和 < code > src/lib.rs< / code > < / li >
< li > 在二进制包中引用 < code > lib< / code > 包< / li >
< li > 使用 < code > pub use< / code > 再导出 API， < / li >
< / ul >
< p > 首先，使用 < code > cargo new art< / code > 创建一个 Package < code > art< / code > ： < / p >
< pre > < code class = "language-console" > Created binary (application) `art` package
< / code > < / pre >
< p > 系统提示我们创建了一个二进制 < code > Package< / code > ，根据< a href = "https://course.rs/basic/crate-module/crate.html" > 之前章节< / a > 学过的内容，可以知道该 < code > Package< / code > 包含一个同名的二进制包：包名为 < code > art< / code > ，包根为 < code > src/main.rs< / code > ，该包可以编译成二进制然后运行。< / p >
< p > 现在，在 < code > src< / code > 目录下创建一个 < code > lib.rs< / code > 文件，同样，根据之前学习的知识，创建该文件等于又创建了一个库类型的包，包名也是 < code > art< / code > ，包根为 < code > src/lib.rs< / code > ，该包是是库类型的，因此往往作为依赖库被引入。< / p >
< p > 将以下内容添加到 < code > src/lib.rs< / code > 中：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > //! # Art
//!
//! 未来的艺术建模库，现在的调色库
pub use self::kinds::PrimaryColor;
pub use self::kinds::SecondaryColor;
pub use self::utils::mix;
pub mod kinds {
//! 定义颜色的类型
/// 主色
pub enum PrimaryColor {
Red,
Yellow,
Blue,
}
/// 副色
#[derive(Debug,PartialEq)]
pub enum SecondaryColor {
Orange,
Green,
Purple,
}
}
pub mod utils {
//! 实用工具，目前只实现了调色板
use crate::kinds::*;
/// 将两种主色调成副色
/// ```rust
/// use art::utils::mix;
/// use art::kinds::{PrimaryColor,SecondaryColor};
/// assert!(matches!(mix(PrimaryColor::Yellow, PrimaryColor::Blue), SecondaryColor::Green));
/// ```
pub fn mix(c1: PrimaryColor, c2: PrimaryColor) -> SecondaryColor {
SecondaryColor::Green
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 在库包的包根 < code > src/lib.rs< / code > 下，我们又定义了几个子模块，同时将子模块中的三个项通过 < code > pub use< / code > 进行了再导出。< / p >
< p > 接着，将下面内容添加到 < code > src/main.rs< / code > 中：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use art::kinds::PrimaryColor;
use art::utils::mix;
fn main() {
let blue = PrimaryColor::Blue;
let yellow = PrimaryColor::Yellow;
println!("{:?}",mix(blue, yellow));
}< / code > < / pre >
< p > 在二进制可执行包的包根 < code > src/main.rs< / code > 下，我们引入了库包 < code > art< / code > 中的模块项，同时使用 < code > main< / code > 函数作为程序的入口，该二进制包可以使用 < code > cargo run< / code > 运行：< / p >
< pre > < code class = "language-console" > Green
< / code > < / pre >
< p > 至此，库包完美提供了用于调色的 API， < / p >
< p > 最后，再来看看文档长啥样：< / p >
< img alt = "" src = "https://pic1.zhimg.com/80/v2-e9ef7351458fd01020b35990c3daf222_1440w.png" class = "center" / >
< h2 id = "总结" > < a class = "header" href = "#总结" > 总结< / a > < / h2 >
< p > 在 Rust 中，注释分为三个主要类型：代码注释、文档注释、包和模块注释，每个注释类型都拥有两种形式：行注释和块注释，熟练掌握包模块和注释的知识，非常有助于我们创建工程性更强的项目。< / p >
< p > 如果读者看到这里对于包模块还是有些模糊，强烈建议回头看看相关的章节以及本章节的最后一个综合例子。< / 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/comments-docs.html" > Rust By Practice< / a > ，支持代码在线编辑和运行，并提供详细的习题解答。（本节暂无习题解答）< / p >
< / blockquote >
< / main >
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