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36 lines
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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="Safely transmutes a value of one type to a value of another type of the same size."><title>transmute in zerocopy - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.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"href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="zerocopy" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../static.files/storage-e2aeef58.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.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]--><rustdoc-topbar><h2><a href="#">transmute</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../zerocopy/index.html">zerocopy</a><span class="version">0.8.39</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">transmute</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#allowshrink" title="`#![allow(shrink)]`"><code>#![allow(shrink)]</code></a></li><li><a href="#examples" title="Examples">Examples</a></li><li><a href="#use-in-const-contexts" title="Use in `const` contexts">Use in <code>const</code> contexts</a></li></ul></section><div id="rustdoc-modnav"><h2 class="in-crate"><a href="index.html">In crate zerocopy</a></h2></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><div class="rustdoc-breadcrumbs"><a href="index.html">zerocopy</a></div><h1>Macro <span class="macro">transmute</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/zerocopy/macros.rs.html#64-185">Source</a> </span></div><pre class="rust item-decl"><code>macro_rules! transmute {
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(#![allow(shrink)] $e:expr) => { ... };
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($e:expr) => { ... };
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}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Safely transmutes a value of one type to a value of another type of the same
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size.</p>
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<p>This macro behaves like an invocation of this function:</p>
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<div class="example-wrap ignore"><a href="#" class="tooltip" title="This example is not tested">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="kw">const fn </span>transmute<Src, Dst>(src: Src) -> Dst
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<span class="kw">where
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</span>Src: IntoBytes,
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Dst: FromBytes,
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size_of::<Src>() == size_of::<Dst>(),
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{
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...
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}</code></pre></div>
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<p>However, unlike a function, this macro can only be invoked when the types of
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<code>Src</code> and <code>Dst</code> are completely concrete. The types <code>Src</code> and <code>Dst</code> are
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inferred from the calling context; they cannot be explicitly specified in
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the macro invocation.</p>
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<p>Note that the <code>Src</code> produced by the expression <code>$e</code> will <em>not</em> be dropped.
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Semantically, its bits will be copied into a new value of type <code>Dst</code>, the
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original <code>Src</code> will be forgotten, and the value of type <code>Dst</code> will be
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returned.</p>
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<h2 id="allowshrink"><a class="doc-anchor" href="#allowshrink">§</a><code>#![allow(shrink)]</code></h2>
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<p>If <code>#![allow(shrink)]</code> is provided, <code>transmute!</code> additionally supports
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transmutations that shrink the size of the value; e.g.:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span>u: u32 = <span class="macro">transmute!</span>(<span class="attr">#![allow(shrink)] </span><span class="number">0u64</span>);
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<span class="macro">assert_eq!</span>(u, <span class="number">0u32</span>);</code></pre></div><h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span>one_dimensional: [u8; <span class="number">8</span>] = [<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>, <span class="number">6</span>, <span class="number">7</span>];
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<span class="kw">let </span>two_dimensional: [[u8; <span class="number">4</span>]; <span class="number">2</span>] = <span class="macro">transmute!</span>(one_dimensional);
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<span class="macro">assert_eq!</span>(two_dimensional, [[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>], [<span class="number">4</span>, <span class="number">5</span>, <span class="number">6</span>, <span class="number">7</span>]]);</code></pre></div><h2 id="use-in-const-contexts"><a class="doc-anchor" href="#use-in-const-contexts">§</a>Use in <code>const</code> contexts</h2>
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<p>This macro can be invoked in <code>const</code> contexts.</p>
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</div></details></section></div></main></body></html> |