| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="A macro that creates a projection type covering all the fields of struct."><meta name="keywords" content="rust, rustlang, rust-lang, pin_project"><title>pin_project in pin_project_lite - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.svg"></head><body class="rustdoc macro"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../pin_project_lite/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../pin_project_lite/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In pin_project_lite</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Macro <a href="index.html">pin_project_lite</a>::<wbr><a class="macro" href="#">pin_project</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/pin_project_lite/lib.rs.html#291-298">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><div class="example-wrap"><pre class="rust macro"><code><span class="macro">macro_rules! </span>pin_project { |
| ($(<span class="macro-nonterminal">$tt</span>:tt)<span class="kw-2">*</span>) => { ... }; |
| }</code></pre></div> |
| </div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A macro that creates a projection type covering all the fields of struct.</p> |
| <p>This macro creates a projection type according to the following rules:</p> |
| <ul> |
| <li>For the field that uses <code>#[pin]</code> attribute, makes the pinned reference to the field.</li> |
| <li>For the other fields, makes the unpinned reference to the field.</li> |
| </ul> |
| <p>And the following methods are implemented on the original type:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">fn </span>project(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) -> Projection<<span class="lifetime">'_</span>>; |
| <span class="kw">fn </span>project_ref(<span class="self">self</span>: Pin<<span class="kw-2">&</span><span class="self">Self</span>>) -> ProjectionRef<<span class="lifetime">'_</span>>;</code></pre></div> |
| <p>By passing an attribute with the same name as the method to the macro, |
| you can name the projection type returned from the method. This allows you |
| to use pattern matching on the projected types.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="macro">pin_project! </span>{ |
| <span class="attribute">#[project = EnumProj] |
| </span><span class="kw">enum </span>Enum<T> { |
| Variant { <span class="attribute">#[pin] </span>field: T }, |
| } |
| } |
| |
| <span class="kw">impl</span><T> Enum<T> { |
| <span class="kw">fn </span>method(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) { |
| <span class="kw">let </span>this: EnumProj<<span class="lifetime">'_</span>, T> = <span class="self">self</span>.project(); |
| <span class="kw">match </span>this { |
| EnumProj::Variant { field } => { |
| <span class="kw">let _</span>: Pin<<span class="kw-2">&mut </span>T> = field; |
| } |
| } |
| } |
| }</code></pre></div> |
| <p>By passing the <code>#[project_replace = MyProjReplace]</code> attribute you may create an additional |
| method which allows the contents of <code>Pin<&mut Self></code> to be replaced while simultaneously moving |
| out all unpinned fields in <code>Self</code>.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">fn </span>project_replace(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>, replacement: <span class="self">Self</span>) -> MyProjReplace;</code></pre></div> |
| <p>Also, note that the projection types returned by <code>project</code> and <code>project_ref</code> have |
| an additional lifetime at the beginning of generics.</p> |
| <div class="example-wrap"><pre class="language-text"><code>let this: EnumProj<'_, T> = self.project(); |
| ^^</code></pre></div> |
| <p>The visibility of the projected types and projection methods is based on the |
| original type. However, if the visibility of the original type is <code>pub</code>, the |
| visibility of the projected types and the projection methods is downgraded |
| to <code>pub(crate)</code>.</p> |
| <h2 id="safety"><a href="#safety">Safety</a></h2> |
| <p><code>pin_project!</code> macro guarantees safety in much the same way as <a href="https://github.com/taiki-e/pin-project">pin-project</a> crate. |
| Both are completely safe unless you write other unsafe code.</p> |
| <p>See <a href="https://github.com/taiki-e/pin-project">pin-project</a> crate for more details.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::pin::Pin; |
| |
| <span class="kw">use </span>pin_project_lite::pin_project; |
| |
| <span class="macro">pin_project! </span>{ |
| <span class="kw">struct </span>Struct<T, U> { |
| <span class="attribute">#[pin] |
| </span>pinned: T, |
| unpinned: U, |
| } |
| } |
| |
| <span class="kw">impl</span><T, U> Struct<T, U> { |
| <span class="kw">fn </span>method(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) { |
| <span class="kw">let </span>this = <span class="self">self</span>.project(); |
| <span class="kw">let _</span>: Pin<<span class="kw-2">&mut </span>T> = this.pinned; <span class="comment">// Pinned reference to the field |
| </span><span class="kw">let _</span>: <span class="kw-2">&mut </span>U = this.unpinned; <span class="comment">// Normal reference to the field |
| </span>} |
| }</code></pre></div> |
| <p>To use <code>pin_project!</code> on enums, you need to name the projection type |
| returned from the method.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::pin::Pin; |
| |
| <span class="kw">use </span>pin_project_lite::pin_project; |
| |
| <span class="macro">pin_project! </span>{ |
| <span class="attribute">#[project = EnumProj] |
| </span><span class="kw">enum </span>Enum<T> { |
| Struct { |
| <span class="attribute">#[pin] |
| </span>field: T, |
| }, |
| Unit, |
| } |
| } |
| |
| <span class="kw">impl</span><T> Enum<T> { |
| <span class="kw">fn </span>method(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) { |
| <span class="kw">match </span><span class="self">self</span>.project() { |
| EnumProj::Struct { field } => { |
| <span class="kw">let _</span>: Pin<<span class="kw-2">&mut </span>T> = field; |
| } |
| EnumProj::Unit => {} |
| } |
| } |
| }</code></pre></div> |
| <p>If you want to call the <code>project()</code> method multiple times or later use the |
| original <a href="https://doc.rust-lang.org/nightly/core/pin/struct.Pin.html"><code>Pin</code></a> type, it needs to use <a href="https://doc.rust-lang.org/nightly/core/pin/struct.Pin.html#method.as_mut"><code>.as_mut()</code></a> to avoid |
| consuming the <a href="https://doc.rust-lang.org/nightly/core/pin/struct.Pin.html"><code>Pin</code></a>.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::pin::Pin; |
| |
| <span class="kw">use </span>pin_project_lite::pin_project; |
| |
| <span class="macro">pin_project! </span>{ |
| <span class="kw">struct </span>Struct<T> { |
| <span class="attribute">#[pin] |
| </span>field: T, |
| } |
| } |
| |
| <span class="kw">impl</span><T> Struct<T> { |
| <span class="kw">fn </span>call_project_twice(<span class="kw-2">mut </span><span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) { |
| <span class="comment">// `project` consumes `self`, so reborrow the `Pin<&mut Self>` via `as_mut`. |
| </span><span class="self">self</span>.as_mut().project(); |
| <span class="self">self</span>.as_mut().project(); |
| } |
| }</code></pre></div> |
| <h2 id="unpin"><a href="#unpin"><code>!Unpin</code></a></h2> |
| <p>If you want to ensure that <a href="https://doc.rust-lang.org/nightly/core/marker/trait.Unpin.html" title="Unpin"><code>Unpin</code></a> is not implemented, use <code>#[pin]</code> |
| attribute for a <a href="https://doc.rust-lang.org/nightly/core/marker/struct.PhantomPinned.html"><code>PhantomPinned</code></a> field.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::marker::PhantomPinned; |
| |
| <span class="kw">use </span>pin_project_lite::pin_project; |
| |
| <span class="macro">pin_project! </span>{ |
| <span class="kw">struct </span>Struct<T> { |
| field: T, |
| <span class="attribute">#[pin] </span><span class="comment">// <------ This `#[pin]` is required to make `Struct` to `!Unpin`. |
| </span>_pin: PhantomPinned, |
| } |
| }</code></pre></div> |
| <p>Note that using <a href="https://doc.rust-lang.org/nightly/core/marker/struct.PhantomPinned.html"><code>PhantomPinned</code></a> without <code>#[pin]</code> attribute has no effect.</p> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="pin_project_lite" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
