89 lines
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89 lines
7.2 KiB
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<!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="Derive the `Zeroable` trait for a type."><title>Zeroable in bytemuck - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-42caa33d.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="bytemuck" data-themes="" data-resource-suffix="" data-rustdoc-version="1.84.0 (9fc6b4312 2025-01-07)" data-channel="1.84.0" data-search-js="search-92e6798f.js" data-settings-js="settings-0f613d39.js" ><script src="../static.files/storage-59e33391.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-5f194d8c.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-893ab5e7.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-6580c154.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.svg"></head><body class="rustdoc derive"><!--[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" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../bytemuck/index.html">bytemuck</a><span class="version">1.21.0</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">Zeroable</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#example" title="Example">Example</a></li><li><a href="#custom-bounds" title="Custom bounds">Custom bounds</a><ul><li><a href="#examples" title="Examples">Examples</a></li></ul></li></ul></section><div id="rustdoc-modnav"><h2 class="in-crate"><a href="index.html">In crate bytemuck</a></h2></div></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><span class="rustdoc-breadcrumbs"><a href="index.html">bytemuck</a></span><h1>Derive Macro <span class="derive">Zeroable</span><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/bytemuck_derive/lib.rs.html#237-239">Source</a> </span></div><pre class="rust item-decl"><code>#[derive(Zeroable)]
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{
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<span class="comment">// Attributes available to this derive:</span>
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#[bytemuck]
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#[zeroable]
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}
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</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Derive the <code>Zeroable</code> trait for a type.</p>
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<p>The macro ensures that the type follows all the the safety requirements
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for the <code>Zeroable</code> trait.</p>
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<p>The following constraints need to be satisfied for the macro to succeed on a
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struct:</p>
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<ul>
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<li>All fields in the struct must implement <code>Zeroable</code></li>
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</ul>
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<p>The following constraints need to be satisfied for the macro to succeed on
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an enum:</p>
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<ul>
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<li>The enum has an explicit <code>#[repr(Int)]</code>, <code>#[repr(C)]</code>, or <code>#[repr(C, Int)]</code>.</li>
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<li>The enum has a variant with discriminant 0 (explicitly or implicitly).</li>
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<li>All fields in the variant with discriminant 0 (if any) must implement
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<code>Zeroable</code></li>
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</ul>
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<p>The macro always succeeds on unions.</p>
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<h3 id="example"><a class="doc-anchor" href="#example">§</a>Example</h3>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Copy, Clone, Zeroable)]
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#[repr(C)]
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</span><span class="kw">struct </span>Test {
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a: u16,
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b: u16,
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}</code></pre></div>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Copy, Clone, Zeroable)]
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#[repr(i32)]
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</span><span class="kw">enum </span>Values {
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A = <span class="number">0</span>,
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B = <span class="number">1</span>,
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C = <span class="number">2</span>,
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}
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<span class="attr">#[derive(Clone, Zeroable)]
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#[repr(C)]
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</span><span class="kw">enum </span>Implicit {
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A(bool, u8, char),
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B(String),
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C(std::num::NonZeroU8),
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}</code></pre></div>
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<h2 id="custom-bounds"><a class="doc-anchor" href="#custom-bounds">§</a>Custom bounds</h2>
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<p>Custom bounds for the derived <code>Zeroable</code> impl can be given using the
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<code>#[zeroable(bound = "")]</code> helper attribute.</p>
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<p>Using this attribute additionally opts-in to “perfect derive” semantics,
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where instead of adding bounds for each generic type parameter, bounds are
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added for each field’s type.</p>
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<h3 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h3>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Clone, Zeroable)]
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#[zeroable(bound = <span class="string">""</span>)]
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</span><span class="kw">struct </span>AlwaysZeroable<T> {
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a: PhantomData<T>,
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}
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AlwaysZeroable::<std::num::NonZeroU8>::zeroed();</code></pre></div>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Copy, Clone, Zeroable)]
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#[repr(u8)]
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#[zeroable(bound = <span class="string">""</span>)]
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</span><span class="kw">enum </span>MyOption<T> {
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<span class="prelude-val">None</span>,
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<span class="prelude-val">Some</span>(T),
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}
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<span class="macro">assert!</span>(<span class="macro">matches!</span>(MyOption::<std::num::NonZeroU8>::zeroed(), MyOption::None));</code></pre></div>
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<div class="example-wrap compile_fail"><a href="#" class="tooltip" title="This example deliberately fails to compile">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Clone, Zeroable)]
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#[zeroable(bound = <span class="string">"T: Copy"</span>)]
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</span><span class="kw">struct </span>ZeroableWhenTIsCopy<T> {
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a: PhantomData<T>,
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}
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ZeroableWhenTIsCopy::<String>::zeroed();</code></pre></div>
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<p>The restriction that all fields must be Zeroable is still applied, and this
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is enforced using the mentioned “perfect derive” semantics.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Clone, Zeroable)]
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#[zeroable(bound = <span class="string">""</span>)]
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</span><span class="kw">struct </span>ZeroableWhenTIsZeroable<T> {
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a: T,
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}
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ZeroableWhenTIsZeroable::<u32>::zeroed();</code></pre></div>
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<div class="example-wrap compile_fail"><a href="#" class="tooltip" title="This example deliberately fails to compile">ⓘ</a><pre class="rust rust-example-rendered"><code>ZeroableWhenTIsZeroable::<String>::zeroed();</code></pre></div>
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</div></details></section></div></main></body></html> |