| <!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="An attribute that creates projection types covering all the fields of struct or enum."><meta name="keywords" content="rust, rustlang, rust-lang, pin_project"><title>pin_project in pin_project - 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 attr"><!--[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/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/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</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">Attribute Macro <a href="index.html">pin_project</a>::<wbr><a class="attr" 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 id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust attr"><code>#[pin_project]</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>An attribute that creates projection types covering all the fields of |
| struct or enum.</p> |
| <p>This attribute creates projection types according to the following rules:</p> |
| <ul> |
| <li>For the fields that use <code>#[pin]</code> attribute, create the pinned reference to |
| the field.</li> |
| <li>For the other fields, create a normal 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 argument with the same name as the method to the attribute, |
| 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="attribute">#[pin_project(project = EnumProj)] |
| </span><span class="kw">enum </span>Enum<T> { |
| Variant(<span class="attribute">#[pin] </span>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(x) => { |
| <span class="kw">let _</span>: Pin<<span class="kw-2">&mut </span>T> = x; |
| } |
| } |
| } |
| }</code></pre></div> |
| <p>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>This attribute is completely safe. In the absence of other <code>unsafe</code> code |
| <em>that you write</em>, it is impossible to cause <a href="https://doc.rust-lang.org/reference/behavior-considered-undefined.html">undefined |
| behavior</a> with this attribute.</p> |
| <p>This is accomplished by enforcing the four requirements for pin projection |
| stated in <a href="core::pin#projections-and-structural-pinning">the Rust documentation</a>:</p> |
| <ol> |
| <li> |
| <p>The struct must only be [<code>Unpin</code>] if all the structural fields are |
| [<code>Unpin</code>].</p> |
| <p>To enforce this, this attribute will automatically generate an [<code>Unpin</code>] |
| implementation for you, which will require that all structurally pinned |
| fields be [<code>Unpin</code>].</p> |
| <p>If you attempt to provide an [<code>Unpin</code>] impl, the blanket impl will then |
| apply to your type, causing a compile-time error due to the conflict with |
| the second impl.</p> |
| <p>If you wish to provide a manual [<code>Unpin</code>] impl, you can do so via the |
| <a href="attr.pin_project.html#unsafeunpin"><code>UnsafeUnpin</code></a> argument.</p> |
| </li> |
| <li> |
| <p>The destructor of the struct must not move structural fields out of its |
| argument.</p> |
| <p>To enforce this, this attribute will generate code like this:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">struct </span>MyStruct {} |
| <span class="kw">trait </span>MyStructMustNotImplDrop {} |
| <span class="kw">impl</span><T: Drop> MyStructMustNotImplDrop <span class="kw">for </span>T {} |
| <span class="kw">impl </span>MyStructMustNotImplDrop <span class="kw">for </span>MyStruct {}</code></pre></div> |
| <p>If you attempt to provide an [<code>Drop</code>] impl, the blanket impl will then |
| apply to your type, causing a compile-time error due to the conflict with |
| the second impl.</p> |
| <p>If you wish to provide a custom [<code>Drop</code>] impl, you can annotate an impl |
| with <a href="attr.pin_project.html#pinned_drop"><code>#[pinned_drop]</code></a>. This impl takes a pinned version of |
| your struct - that is, <a href="core::pin::Pin"><code>Pin</code></a><code><&mut MyStruct></code> where <code>MyStruct</code> is the |
| type of your struct.</p> |
| <p>You can call <code>.project()</code> on this type as usual, along with any other |
| methods you have defined. Because your code is never provided with |
| a <code>&mut MyStruct</code>, it is impossible to move out of pin-projectable |
| fields in safe code in your destructor.</p> |
| </li> |
| <li> |
| <p>You must make sure that you uphold the <a href="core::pin#drop-guarantee"><code>Drop</code> |
| guarantee</a>: once your struct is pinned, the memory that |
| contains the content is not overwritten or deallocated without calling |
| the content’s destructors.</p> |
| <p>Safe code doesn’t need to worry about this - the only way to violate |
| this requirement is to manually deallocate memory (which is <code>unsafe</code>), |
| or to overwrite a field with something else. |
| Because your custom destructor takes <a href="core::pin::Pin"><code>Pin</code></a><code><&mut MyStruct></code>, it’s |
| impossible to obtain a mutable reference to a pin-projected field in safe |
| code.</p> |
| </li> |
| <li> |
| <p>You must not offer any other operations that could lead to data being |
| moved out of the structural fields when your type is pinned.</p> |
| <p>As with requirement 3, it is impossible for safe code to violate this. |
| This crate ensures that safe code can never obtain a mutable reference to |
| <code>#[pin]</code> fields, which prevents you from ever moving out of them in safe |
| code.</p> |
| </li> |
| </ol> |
| <p>Pin projections are also incompatible with <a href="https://doc.rust-lang.org/nomicon/other-reprs.html#reprpacked"><code>#[repr(packed)]</code></a> |
| types. Attempting to use this attribute on a <code>#[repr(packed)]</code> type results |
| in a compile-time error.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <p><code>#[pin_project]</code> can be used on structs and enums.</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::pin_project; |
| |
| <span class="attribute">#[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="kw">let _</span>: <span class="kw-2">&mut </span>U = this.unpinned; |
| } |
| }</code></pre></div> |
| |
| <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::pin_project; |
| |
| <span class="attribute">#[pin_project] |
| </span><span class="kw">struct </span>TupleStruct<T, U>(<span class="attribute">#[pin] </span>T, U); |
| |
| <span class="kw">impl</span><T, U> TupleStruct<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.<span class="number">0</span>; |
| <span class="kw">let _</span>: <span class="kw-2">&mut </span>U = this.<span class="number">1</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::pin_project; |
| |
| <span class="attribute">#[pin_project(project = EnumProj)] |
| </span><span class="kw">enum </span>Enum<T, U> { |
| Tuple(<span class="attribute">#[pin] </span>T), |
| Struct { field: U }, |
| Unit, |
| } |
| |
| <span class="kw">impl</span><T, U> Enum<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">match </span><span class="self">self</span>.project() { |
| EnumProj::Tuple(x) => { |
| <span class="kw">let _</span>: Pin<<span class="kw-2">&mut </span>T> = x; |
| } |
| EnumProj::Struct { field } => { |
| <span class="kw">let _</span>: <span class="kw-2">&mut </span>U = field; |
| } |
| EnumProj::Unit => {} |
| } |
| } |
| }</code></pre></div> |
| <p>When <code>#[pin_project]</code> is used on enums, only named projection types and |
| methods are generated because there is no way to access variants of |
| projected types without naming it. |
| For example, in the above example, only the <code>project</code> method is generated, |
| and the <code>project_ref</code> method is not generated. |
| (When <code>#[pin_project]</code> is used on structs, both methods are always generated.)</p> |
| |
| <div class="example-wrap compile_fail"><div class='tooltip'>ⓘ</div><pre class="rust rust-example-rendered"><code><span class="kw">impl</span><T, U> Enum<T, U> { |
| <span class="kw">fn </span>call_project_ref(<span class="self">self</span>: Pin<<span class="kw-2">&</span><span class="self">Self</span>>) { |
| <span class="kw">let </span>_this = <span class="self">self</span>.project_ref(); |
| <span class="comment">//~^ ERROR no method named `project_ref` found for struct `Pin<&Enum<T, U>>` in the current scope |
| </span>} |
| }</code></pre></div> |
| <p>If you want to call <code>.project()</code> multiple times or later use the |
| original <a href="core::pin::Pin"><code>Pin</code></a> type, it needs to use <a href="core::pin::Pin::as_mut"><code>.as_mut()</code></a> to avoid |
| consuming the <a href="core::pin::Pin"><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::pin_project; |
| |
| <span class="attribute">#[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 [<code>Unpin</code>] is not implemented, use the <code>!Unpin</code> |
| argument to <code>#[pin_project]</code>.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>pin_project::pin_project; |
| |
| <span class="attribute">#[pin_project(!Unpin)] |
| </span><span class="kw">struct </span>Struct<T> { |
| field: T, |
| }</code></pre></div> |
| <p>This is equivalent to using <code>#[pin]</code> attribute for the <a href="core::marker::PhantomPinned"><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::pin_project; |
| |
| <span class="attribute">#[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="core::marker::PhantomPinned"><code>PhantomPinned</code></a> without <code>#[pin]</code> attribute has no effect.</p> |
| <h2 id="unsafeunpin"><a href="#unsafeunpin"><code>UnsafeUnpin</code></a></h2> |
| <p>If you want to implement [<code>Unpin</code>] manually, you must use the <code>UnsafeUnpin</code> |
| argument to <code>#[pin_project]</code>.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>pin_project::{pin_project, UnsafeUnpin}; |
| |
| <span class="attribute">#[pin_project(UnsafeUnpin)] |
| </span><span class="kw">struct </span>Struct<T, U> { |
| <span class="attribute">#[pin] |
| </span>pinned: T, |
| unpinned: U, |
| } |
| |
| <span class="kw">unsafe impl</span><T: Unpin, U> UnsafeUnpin <span class="kw">for </span>Struct<T, U> {}</code></pre></div> |
| <p>Note the usage of the unsafe <a href="https://docs.rs/pin-project/1/pin_project/trait.UnsafeUnpin.html"><code>UnsafeUnpin</code></a> trait, instead of the usual |
| [<code>Unpin</code>] trait. <a href="https://docs.rs/pin-project/1/pin_project/trait.UnsafeUnpin.html"><code>UnsafeUnpin</code></a> behaves exactly like [<code>Unpin</code>], except that |
| is unsafe to implement. This unsafety comes from the fact that pin |
| projections are being used. If you implement <a href="https://docs.rs/pin-project/1/pin_project/trait.UnsafeUnpin.html"><code>UnsafeUnpin</code></a>, you must |
| ensure that it is only implemented when all pin-projected fields implement |
| [<code>Unpin</code>].</p> |
| <p>See <a href="https://docs.rs/pin-project/1/pin_project/trait.UnsafeUnpin.html"><code>UnsafeUnpin</code></a> trait for more details.</p> |
| <h2 id="pinned_drop"><a href="#pinned_drop"><code>#[pinned_drop]</code></a></h2> |
| <p>In order to correctly implement pin projections, a type’s [<code>Drop</code>] impl must |
| not move out of any structurally pinned fields. Unfortunately, |
| [<code>Drop::drop</code>] takes <code>&mut Self</code>, not <a href="core::pin::Pin"><code>Pin</code></a><code><&mut Self></code>.</p> |
| <p>To ensure that this requirement is upheld, the <code>#[pin_project]</code> attribute |
| will provide a [<code>Drop</code>] impl for you. This [<code>Drop</code>] impl will delegate to |
| an impl block annotated with <code>#[pinned_drop]</code> if you use the <code>PinnedDrop</code> |
| argument to <code>#[pin_project]</code>.</p> |
| <p>This impl block acts just like a normal [<code>Drop</code>] impl, |
| except for the following two:</p> |
| <ul> |
| <li><code>drop</code> method takes <a href="core::pin::Pin"><code>Pin</code></a><code><&mut Self></code></li> |
| <li>Name of the trait is <code>PinnedDrop</code>.</li> |
| </ul> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">pub trait </span>PinnedDrop { |
| <span class="kw">fn </span>drop(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>); |
| }</code></pre></div> |
| <p><code>#[pin_project]</code> implements the actual [<code>Drop</code>] trait via <code>PinnedDrop</code> you |
| implemented. To drop a type that implements <code>PinnedDrop</code>, use the [<code>drop</code>] |
| function just like dropping a type that directly implements [<code>Drop</code>].</p> |
| <p>In particular, it will never be called more than once, just like |
| [<code>Drop::drop</code>].</p> |
| <p>For example:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::{fmt::Debug, pin::Pin}; |
| |
| <span class="kw">use </span>pin_project::{pin_project, pinned_drop}; |
| |
| <span class="attribute">#[pin_project(PinnedDrop)] |
| </span><span class="kw">struct </span>PrintOnDrop<T: Debug, U: Debug> { |
| <span class="attribute">#[pin] |
| </span>pinned_field: T, |
| unpin_field: U, |
| } |
| |
| <span class="attribute">#[pinned_drop] |
| </span><span class="kw">impl</span><T: Debug, U: Debug> PinnedDrop <span class="kw">for </span>PrintOnDrop<T, U> { |
| <span class="kw">fn </span>drop(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) { |
| <span class="macro">println!</span>(<span class="string">"Dropping pinned field: {:?}"</span>, <span class="self">self</span>.pinned_field); |
| <span class="macro">println!</span>(<span class="string">"Dropping unpin field: {:?}"</span>, <span class="self">self</span>.unpin_field); |
| } |
| } |
| |
| <span class="kw">fn </span>main() { |
| <span class="kw">let </span>_x = PrintOnDrop { pinned_field: <span class="bool-val">true</span>, unpin_field: <span class="number">40 </span>}; |
| }</code></pre></div> |
| <p>See also <a href="attr.pinned_drop.html" title="pinned_drop"><code>#[pinned_drop]</code></a> attribute.</p> |
| <h2 id="project_replace-method"><a href="#project_replace-method"><code>project_replace</code> method</a></h2> |
| <p>In addition to the <code>project</code> and <code>project_ref</code> methods which are always |
| provided when you use the <code>#[pin_project]</code> attribute, there is a third |
| method, <code>project_replace</code> which can be useful in some situations. It is |
| equivalent to <a href="core::pin::Pin::set"><code>Pin::set</code></a>, except that the unpinned fields are moved and |
| returned, instead of being dropped in-place.</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>>, other: <span class="self">Self</span>) -> ProjectionOwned;</code></pre></div> |
| <p>The <code>ProjectionOwned</code> type is identical to the <code>Self</code> type, except that |
| all pinned fields have been replaced by equivalent <a href="core::marker::PhantomData"><code>PhantomData</code></a> types.</p> |
| <p>This method is opt-in, because it is only supported for [<code>Sized</code>] types, and |
| because it is incompatible with the <a href="attr.pin_project.html#pinned_drop"><code>#[pinned_drop]</code></a> |
| attribute described above. It can be enabled by using |
| <code>#[pin_project(project_replace)]</code>.</p> |
| <p>For example:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::{marker::PhantomData, pin::Pin}; |
| |
| <span class="kw">use </span>pin_project::pin_project; |
| |
| <span class="attribute">#[pin_project(project_replace)] |
| </span><span class="kw">struct </span>Struct<T, U> { |
| <span class="attribute">#[pin] |
| </span>pinned_field: T, |
| unpinned_field: 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>>, other: <span class="self">Self</span>) { |
| <span class="kw">let </span>this = <span class="self">self</span>.project_replace(other); |
| <span class="kw">let _</span>: U = this.unpinned_field; |
| <span class="kw">let _</span>: PhantomData<T> = this.pinned_field; |
| } |
| }</code></pre></div> |
| <p>By passing the value to the <code>project_replace</code> argument, you can name the |
| returned type of the <code>project_replace</code> method. This is necessary whenever |
| destructuring the return type of the <code>project_replace</code> method, and work in exactly |
| the same way as the <code>project</code> and <code>project_ref</code> arguments.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>pin_project::pin_project; |
| |
| <span class="attribute">#[pin_project(project_replace = EnumProjOwn)] |
| </span><span class="kw">enum </span>Enum<T, U> { |
| A { |
| <span class="attribute">#[pin] |
| </span>pinned_field: T, |
| unpinned_field: U, |
| }, |
| B, |
| } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>x = Box::pin(Enum::A { pinned_field: <span class="number">42</span>, unpinned_field: <span class="string">"hello" </span>}); |
| |
| <span class="kw">match </span>x.as_mut().project_replace(Enum::B) { |
| EnumProjOwn::A { unpinned_field, .. } => <span class="macro">assert_eq!</span>(unpinned_field, <span class="string">"hello"</span>), |
| EnumProjOwn::B => <span class="macro">unreachable!</span>(), |
| }</code></pre></div> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="pin_project" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
