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<main>
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<h1 id="comments-and-docs"><a class="header" href="#comments-and-docs">Comments and Docs</a></h1>
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<p>Every program requires comments:</p>
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<h2 id="comments"><a class="header" href="#comments">Comments</a></h2>
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<ul>
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<li>Regular comments which are ignored by the compiler:
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<ul>
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<li><code>// Line comment, which goes to the end of the line</code></li>
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<li><code>/* Block comment, which goes to the end of the closing delimiter */</code></li>
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</ul>
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</li>
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</ul>
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<h3 id="examples"><a class="header" href="#examples">Examples</a></h3>
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<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
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// This is an example of a line comment
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// There are two slashes at the beginning of the line
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// And nothing written inside these will be read by the compiler
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// println!("Hello, world!");
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// Run it. See? Now try deleting the two slashes, and run it again.
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/*
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* This is another type of comment, a block comment. In general,
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* line comments are the recommended comment style. But
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* block comments are extremely useful for temporarily disabling
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* chunks of code. /* Block comments can be /* nested, */ */
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* so it takes only a few keystrokes to comment out everything
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* in this main() function. /*/*/* Try it yourself! */*/*/
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*/
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/*
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Note: The previous column of `*` was entirely for style. There's
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no actual need for it.
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*/
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}</code></pre></pre>
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<h3 id="exercises"><a class="header" href="#exercises">Exercises</a></h3>
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<ol>
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<li>🌟🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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/* Make it work, only using comments! */
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fn main() {
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todo!();
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unimplemented!();
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assert_eq!(6, 5 + 3 + 2 + 1 )
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}</code></pre></pre>
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<h2 id="doc-comments"><a class="header" href="#doc-comments">Doc Comments</a></h2>
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<ul>
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<li>Doc comments which are parsed into HTML and supported <code>Markdown</code>
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<ul>
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<li><code>/// Generate library docs for the following item</code></li>
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<li><code>//! Generate library docs for the eclosing item</code></li>
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</ul>
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</li>
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</ul>
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<p>Before starting, we need to create a new package for practice: <code>cargo new --lib doc-comments</code>.</p>
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<h3 id="line-doc-comments-"><a class="header" href="#line-doc-comments-">Line doc comments <code>///</code></a></h3>
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<p>Add docs for function <code>add_one</code></p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>// in lib.rs
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/// Add one to the given value and return the value
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///
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/// # Examples
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///
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/// ```
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/// let arg = 5;
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/// let answer = my_crate::add_one(arg);
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///
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/// assert_eq!(6, answer);
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/// ```
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pub fn add_one(x: i32) -> i32 {
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x + 1
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}
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<span class="boring">}</span></code></pre></pre>
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<h3 id="cargo-doc"><a class="header" href="#cargo-doc">Cargo doc</a></h3>
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<p>We can use <code>cargo doc --open</code> to generate html files and open them in the browser.</p>
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<h3 id="block-doc-comments---"><a class="header" href="#block-doc-comments---">Block doc comments <code>/** ... */</code></a></h3>
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<p>Add docs for function <code>add_two</code>:</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>/** Add two to the given value and return a new value
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<span class="boring">Examples
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</span>
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let arg = 5;
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let answer = my_crate::add_two(arg);
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assert_eq!(7, answer);
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*/
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pub fn add_two(x: i32) -> i32 {
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x + 2
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}
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<span class="boring">}</span></code></pre></pre>
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<h3 id="doc-comments-for-crate-and-module"><a class="header" href="#doc-comments-for-crate-and-module">Doc comments for crate and module</a></h3>
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<p>We can also add doc comments for our crates and modules.</p>
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<p>Firstly, let's add some doc comments for our library crate:</p>
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<blockquote>
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<p>Note: We must place crates and module comments at the top of crate root or module file.</p>
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</blockquote>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>//! # Doc comments
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//!
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//! A library for showing how to use doc comments
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// in lib.rs
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pub mod compute;
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<span class="boring">}</span></code></pre></pre>
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<p>You can also use block comments to achieve this:</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>/*! # Doc comments
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A library for showing how to use doc comments */
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<span class="boring">}</span></code></pre></pre>
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<p>Next, create a new module file <code>src/compute.rs</code>, and add following comments to it:</p>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>//! //! Do some complicated arithmetic that you can't do by yourself
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// in compute.rs
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<span class="boring">}</span></code></pre></pre>
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<p>Then run <code>cargo doc --open</code> and see the results.</p>
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<h3 id="doc-tests"><a class="header" href="#doc-tests">Doc tests</a></h3>
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<p>The doc comments of <code>add_one</code> and <code>add_two</code> contain two example code blocks.</p>
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<p>The examples can not only demonstrate how to use your library, but also running as test with <code>cargo test</code> command.</p>
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<ol start="2">
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<li>🌟🌟 But there are errors in the two examples, please fix them, and running with <code>cargo test</code> to get following result:</li>
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</ol>
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<pre><code class="language-shell">running 0 tests
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test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
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Doc-tests doc-comments
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running 2 tests
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test src/lib.rs - add_one (line 11) ... ok
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test src/lib.rs - add_two (line 26) ... ok
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test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.55s
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</code></pre>
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<ol start="3">
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<li>🌟🌟 Sometimes we expect an example to be panic, add following code to <code>src/compute.rs</code> and make the <code>cargo test</code> passed.</li>
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</ol>
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<blockquote>
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<p>You can only modify the comments, DON'T modify <code>fn div</code></p>
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</blockquote>
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<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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|
</span>// in src/compute.rs
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|
|
/// # Panics
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|
///
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/// The function panics if the second argument is zero.
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///
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/// ```rust,should_panic
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|
/// // panics on division by zero
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/// doc_comments::compute::div(10, 0);
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/// ```
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pub fn div(a: i32, b: i32) -> i32 {
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if b == 0 {
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panic!("Divide-by-zero error");
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}
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|
|
a / b
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}
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<span class="boring">}</span></code></pre></pre>
|
|
<ol start="4">
|
|
<li>🌟🌟 Sometimes we want to hide the doc comments, but keep the doc tests.</li>
|
|
</ol>
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<p>Add following code to <code>src/compute.rs</code> ,</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021">// in src/compute.rs
|
|
|
|
/// ```
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|
/// # fn try_main() -> Result<(), String> {
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|
/// # let res = doc_comments::compute::try_div(10, 0)?;
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|
/// # Ok(()) // returning from try_main
|
|
/// # }
|
|
/// # fn main() {
|
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/// # try_main().unwrap();
|
|
/// #
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/// # }
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|
/// ```
|
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pub fn try_div(a: i32, b: i32) -> Result<i32, String> {
|
|
if b == 0 {
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Err(String::from("Divide-by-zero"))
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} else {
|
|
Ok(a / b)
|
|
}
|
|
}</code></pre></pre>
|
|
<p>and modify this code to achieve two goals:</p>
|
|
<ul>
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|
<li>The doc comments must not be presented in html files generated by <code>cargo doc --open</code></li>
|
|
<li>run the tests, you should see results as below:</li>
|
|
</ul>
|
|
<pre><code class="language-shell">running 0 tests
|
|
|
|
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
|
|
|
|
Doc-tests doc-comments
|
|
|
|
running 4 tests
|
|
test src/compute.rs - compute::div (line 7) ... ok
|
|
test src/lib.rs - add_two (line 27) ... ok
|
|
test src/lib.rs - add_one (line 11) ... ok
|
|
test src/compute.rs - compute::try_div (line 20) ... ok
|
|
|
|
test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.51s
|
|
</code></pre>
|
|
<h3 id="code-navigation"><a class="header" href="#code-navigation">Code navigation</a></h3>
|
|
<p>Rust provide a very powerful feature for us, that is code navigation in doc comments.</p>
|
|
<p>Add following code to <code>src/lib.rs</code>:</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>// in lib.rs
|
|
|
|
/// Add three to the given value and return a [`Option`] type
|
|
pub fn add_three(x: i32) -> Option<i32> {
|
|
Some(x + 3)
|
|
}
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<p>Besides jump into the standard library, you can also jump to another module in the package.</p>
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>// in lib.rs
|
|
|
|
mod a {
|
|
/// Add four to the given value and return a [`Option`] type
|
|
/// [`crate::MySpecialFormatter`]
|
|
pub fn add_four(x: i32) -> Option<i32> {
|
|
Some(x + 4)
|
|
}
|
|
}
|
|
|
|
struct MySpecialFormatter;
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<h3 id="doc-attributes"><a class="header" href="#doc-attributes">Doc attributes</a></h3>
|
|
<p>Below are a few examples of the most common <code>#[doc]</code> attributes used with <code>rustdoc</code>.</p>
|
|
<h3 id="inline"><a class="header" href="#inline"><code>inline</code></a></h3>
|
|
<p>Used to inline docs, instead of linking out to separate page.</p>
|
|
<pre><code class="language-rust ignore">#[doc(inline)]
|
|
pub use bar::Bar;
|
|
|
|
/// bar docs
|
|
mod bar {
|
|
/// the docs for Bar
|
|
pub struct Bar;
|
|
}</code></pre>
|
|
<h3 id="no_inline"><a class="header" href="#no_inline"><code>no_inline</code></a></h3>
|
|
<p>Used to prevent linking out to separate page or anywhere.</p>
|
|
<pre><code class="language-rust ignore">// Example from libcore/prelude
|
|
#[doc(no_inline)]
|
|
pub use crate::mem::drop;</code></pre>
|
|
<h3 id="hidden"><a class="header" href="#hidden"><code>hidden</code></a></h3>
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<p>Using this tells <code>rustdoc</code> not to include this in documentation:</p>
|
|
<pre><code class="language-rust editable ignore">// Example from the futures-rs library
|
|
#[doc(hidden)]
|
|
pub use self::async_await::*;</code></pre>
|
|
<p>For documentation, <code>rustdoc</code> is widely used by the community. It's what is used to generate the <a href="https://doc.rust-lang.org/std/">std library docs</a>.</p>
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|
<h3 id="full-code"><a class="header" href="#full-code">Full Code</a></h3>
|
|
<p>The full code of package <code>doc-comments</code> is <a href="https://github.com/sunface/rust-by-practice/tree/master/practices/doc-comments">here</a>.</p>
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