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70 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="Conditionally transmutes a mutable or immutable reference of one type to an immutable reference of another type of the same size and compatible alignment."><title>try_transmute_ref 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="#">try_transmute_ref</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="#">try_<wbr>transmute_<wbr>ref</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#size-compatibility" title="Size compatibility">Size compatibility</a></li><li><a href="#examples" title="Examples">Examples</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">try_<wbr>transmute_<wbr>ref</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#718-749">Source</a> </span></div><pre class="rust item-decl"><code>macro_rules! try_transmute_ref {
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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>Conditionally transmutes a mutable or immutable reference of one type to an
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immutable reference of another type of the same size and compatible
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alignment.</p>
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<p><em>Note that while the <strong>value</strong> of the referent is checked for validity at
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runtime, the <strong>size</strong> and <strong>alignment</strong> are checked at compile time. For
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conversions which are fallible with respect to size and alignment, see the
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methods on <a href="trait.TryFromBytes.html" title="trait zerocopy::TryFromBytes"><code>TryFromBytes</code></a>.</em></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">fn </span>try_transmute_ref<Src, Dst>(src: <span class="kw-2">&</span>Src) -> <span class="prelude-ty">Result</span><<span class="kw-2">&</span>Dst, ValidityError<<span class="kw-2">&</span>Src, Dst>>
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<span class="kw">where
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</span>Src: IntoBytes + Immutable + <span class="question-mark">?</span>Sized,
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Dst: TryFromBytes + Immutable + <span class="question-mark">?</span>Sized,
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align_of::<Src>() >= align_of::<Dst>(),
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size_compatible::<Src, Dst>(),
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{
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...
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}</code></pre></div>
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<p>The types <code>Src</code> and <code>Dst</code> are inferred from the calling context; they cannot
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be explicitly specified in the macro invocation.</p>
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<h2 id="size-compatibility"><a class="doc-anchor" href="#size-compatibility">§</a>Size compatibility</h2>
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<p><code>try_transmute_ref!</code> supports transmuting between <code>Sized</code> types, between
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unsized (i.e., <code>?Sized</code>) types, and from a <code>Sized</code> type to an unsized type.
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It supports any transmutation that preserves the number of bytes of the
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referent, even if doing so requires updating the metadata stored in an
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unsized “fat” reference:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span>src: <span class="kw-2">&</span>[[u8; <span class="number">2</span>]] = <span class="kw-2">&</span>[[<span class="number">0</span>, <span class="number">1</span>], [<span class="number">2</span>, <span class="number">3</span>]][..];
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<span class="kw">let </span>dst: <span class="kw-2">&</span>[u8] = <span class="macro">try_transmute_ref!</span>(src).unwrap();
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<span class="macro">assert_eq!</span>(src.len(), <span class="number">2</span>);
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<span class="macro">assert_eq!</span>(dst.len(), <span class="number">4</span>);
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<span class="macro">assert_eq!</span>(dst, [<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]);
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<span class="macro">assert_eq!</span>(size_of_val(src), size_of_val(dst));</code></pre></div><h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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<p>Transmuting between <code>Sized</code> types:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// 0u8 → bool = false
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</span><span class="macro">assert_eq!</span>(<span class="macro">try_transmute_ref!</span>(<span class="kw-2">&</span><span class="number">0u8</span>), <span class="prelude-val">Ok</span>(<span class="kw-2">&</span><span class="bool-val">false</span>));
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<span class="comment">// 1u8 → bool = true
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</span><span class="macro">assert_eq!</span>(<span class="macro">try_transmute_ref!</span>(<span class="kw-2">&</span><span class="number">1u8</span>), <span class="prelude-val">Ok</span>(<span class="kw-2">&</span><span class="bool-val">true</span>));
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<span class="comment">// 2u8 → bool = error
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</span><span class="macro">assert!</span>(<span class="macro">matches!</span>(
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<span class="macro">try_transmute_ref!</span>(<span class="kw-2">&</span><span class="number">2u8</span>),
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<span class="prelude-ty">Result</span>::<<span class="kw-2">&</span>bool, <span class="kw">_</span>>::Err(ValidityError { .. })
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));</code></pre></div>
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<p>Transmuting between unsized types:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(KnownLayout, FromBytes, IntoBytes, Immutable)]
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#[repr(C)]
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</span><span class="kw">struct </span>SliceDst<T, U> {
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t: T,
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u: [U],
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}
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<span class="kw">type </span>Src = SliceDst<u32, u16>;
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<span class="kw">type </span>Dst = SliceDst<u16, bool>;
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<span class="kw">let </span>src = Src::ref_from_bytes(<span class="kw-2">&</span>[<span class="number">0</span>, <span class="number">1</span>, <span class="number">0</span>, <span class="number">1</span>, <span class="number">0</span>, <span class="number">1</span>, <span class="number">0</span>, <span class="number">1</span>]).unwrap();
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<span class="kw">let </span>dst: <span class="kw-2">&</span>Dst = <span class="macro">try_transmute_ref!</span>(src).unwrap();
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<span class="macro">assert_eq!</span>(src.t.as_bytes(), [<span class="number">0</span>, <span class="number">1</span>, <span class="number">0</span>, <span class="number">1</span>]);
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<span class="macro">assert_eq!</span>(src.u.len(), <span class="number">2</span>);
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<span class="macro">assert_eq!</span>(src.u.as_bytes(), [<span class="number">0</span>, <span class="number">1</span>, <span class="number">0</span>, <span class="number">1</span>]);
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<span class="macro">assert_eq!</span>(dst.t.as_bytes(), [<span class="number">0</span>, <span class="number">1</span>]);
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<span class="macro">assert_eq!</span>(dst.u, [<span class="bool-val">false</span>, <span class="bool-val">true</span>, <span class="bool-val">false</span>, <span class="bool-val">true</span>, <span class="bool-val">false</span>, <span class="bool-val">true</span>]);</code></pre></div></div></details></section></div></main></body></html> |