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72 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="This crate gives small utilities for casting between plain data types."><title>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="../crates.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 mod crate"><!--[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"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#basics" title="Basics">Basics</a></li><li><a href="#failures" title="Failures">Failures</a></li><li><a href="#using-your-own-types" title="Using Your Own Types">Using Your Own Types</a></li><li><a href="#cargo-features" title="Cargo Features">Cargo Features</a></li></ul><h3><a href="#reexports">Crate Items</a></h3><ul class="block"><li><a href="#reexports" title="Re-exports">Re-exports</a></li><li><a href="#modules" title="Modules">Modules</a></li><li><a href="#macros" title="Macros">Macros</a></li><li><a href="#enums" title="Enums">Enums</a></li><li><a href="#traits" title="Traits">Traits</a></li><li><a href="#functions" title="Functions">Functions</a></li><li><a href="#derives" title="Derive Macros">Derive Macros</a></li></ul></section><div id="rustdoc-modnav"></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"><h1>Crate <span>bytemuck</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/lib.rs.html#1-566">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>This crate gives small utilities for casting between plain data types.</p>
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<h3 id="basics"><a class="doc-anchor" href="#basics">§</a>Basics</h3>
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<p>Data comes in five basic forms in Rust, so we have five basic casting
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functions:</p>
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<ul>
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<li><code>T</code> uses <a href="fn.cast.html" title="fn bytemuck::cast"><code>cast</code></a></li>
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<li><code>&T</code> uses <a href="fn.cast_ref.html" title="fn bytemuck::cast_ref"><code>cast_ref</code></a></li>
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<li><code>&mut T</code> uses <a href="fn.cast_mut.html" title="fn bytemuck::cast_mut"><code>cast_mut</code></a></li>
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<li><code>&[T]</code> uses <a href="fn.cast_slice.html" title="fn bytemuck::cast_slice"><code>cast_slice</code></a></li>
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<li><code>&mut [T]</code> uses <a href="fn.cast_slice_mut.html" title="fn bytemuck::cast_slice_mut"><code>cast_slice_mut</code></a></li>
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</ul>
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<p>Depending on the function, the <a href="trait.NoUninit.html" title="trait bytemuck::NoUninit"><code>NoUninit</code></a> and/or <a href="trait.AnyBitPattern.html" title="trait bytemuck::AnyBitPattern"><code>AnyBitPattern</code></a> traits
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are used to maintain memory safety.</p>
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<p><strong>Historical Note:</strong> When the crate first started the <a href="trait.Pod.html" title="trait bytemuck::Pod"><code>Pod</code></a> trait was used
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instead, and so you may hear people refer to that, but it has the strongest
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requirements and people eventually wanted the more fine-grained system, so
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here we are. All types that impl <code>Pod</code> have a blanket impl to also support
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<code>NoUninit</code> and <code>AnyBitPattern</code>. The traits unfortunately do not have a
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perfectly clean hierarchy for semver reasons.</p>
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<h3 id="failures"><a class="doc-anchor" href="#failures">§</a>Failures</h3>
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<p>Some casts will never fail, and other casts might fail.</p>
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<ul>
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<li><code>cast::<u32, f32></code> always works (and <a href="https://doc.rust-lang.org/1.84.0/core/primitive.f32.html#method.from_bits" title="associated function f32::from_bits"><code>f32::from_bits</code></a>).</li>
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<li><code>cast_ref::<[u8; 4], u32></code> might fail if the specific array reference
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given at runtime doesn’t have alignment 4.</li>
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</ul>
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<p>In addition to the “normal” forms of each function, which will panic on
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invalid input, there’s also <code>try_</code> versions which will return a <code>Result</code>.</p>
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<p>If you would like to statically ensure that a cast will work at runtime you
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can use the <code>must_cast</code> crate feature and the <code>must_</code> casting functions. A
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“must cast” that can’t be statically known to be valid will cause a
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compilation error (and sometimes a very hard to read compilation error).</p>
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<h3 id="using-your-own-types"><a class="doc-anchor" href="#using-your-own-types">§</a>Using Your Own Types</h3>
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<p>All the functions listed above are guarded by the <a href="trait.Pod.html" title="trait bytemuck::Pod"><code>Pod</code></a> trait, which is a
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sub-trait of the <a href="trait.Zeroable.html" title="trait bytemuck::Zeroable"><code>Zeroable</code></a> trait.</p>
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<p>If you enable the crate’s <code>derive</code> feature then these traits can be derived
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on your own types. The derive macros will perform the necessary checks on
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your type declaration, and trigger an error if your type does not qualify.</p>
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<p>The derive macros might not cover all edge cases, and sometimes they will
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error when actually everything is fine. As a last resort you can impl these
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traits manually. However, these traits are <code>unsafe</code>, and you should
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carefully read the requirements before using a manual implementation.</p>
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<h3 id="cargo-features"><a class="doc-anchor" href="#cargo-features">§</a>Cargo Features</h3>
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<p>The crate supports Rust 1.34 when no features are enabled, and so there’s
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cargo features for thing that you might consider “obvious”.</p>
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<p>The cargo features <strong>do not</strong> promise any particular MSRV, and they may
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increase their MSRV in new versions.</p>
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<ul>
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<li><code>derive</code>: Provide derive macros for the various traits.</li>
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<li><code>extern_crate_alloc</code>: Provide utilities for <code>alloc</code> related types such as
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Box and Vec.</li>
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<li><code>zeroable_maybe_uninit</code> and <code>zeroable_atomics</code>: Provide more <a href="trait.Zeroable.html" title="trait bytemuck::Zeroable"><code>Zeroable</code></a>
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impls.</li>
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<li><code>wasm_simd</code> and <code>aarch64_simd</code>: Support more SIMD types.</li>
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<li><code>min_const_generics</code>: Provides appropriate impls for arrays of all lengths
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instead of just for a select list of array lengths.</li>
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<li><code>must_cast</code>: Provides the <code>must_</code> functions, which will compile error if
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the requested cast can’t be statically verified.</li>
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<li><code>const_zeroed</code>: Provides a const version of the <code>zeroed</code> function.</li>
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</ul>
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</div></details><h2 id="reexports" class="section-header">Re-exports<a href="#reexports" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name" id="reexport.CheckedBitPattern"><code>pub use checked::<a class="trait" href="checked/trait.CheckedBitPattern.html" title="trait bytemuck::checked::CheckedBitPattern">CheckedBitPattern</a>;</code></div></li><li><div class="item-name"><code>pub use <a class="mod" href="allocation/index.html" title="mod bytemuck::allocation">allocation</a>::*;</code></div></li></ul><h2 id="modules" class="section-header">Modules<a href="#modules" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="mod" href="allocation/index.html" title="mod bytemuck::allocation">allocation</a></div><div class="desc docblock-short">Stuff to boost things in the <code>alloc</code> crate.</div></li><li><div class="item-name"><a class="mod" href="checked/index.html" title="mod bytemuck::checked">checked</a></div><div class="desc docblock-short">Checked versions of the casting functions exposed in crate root
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that support <a href="checked/trait.CheckedBitPattern.html" title="trait bytemuck::checked::CheckedBitPattern"><code>CheckedBitPattern</code></a> types.</div></li></ul><h2 id="macros" class="section-header">Macros<a href="#macros" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="macro" href="macro.offset_of.html" title="macro bytemuck::offset_of">offset_<wbr>of</a></div><div class="desc docblock-short">Find the offset in bytes of the given <code>$field</code> of <code>$Type</code>. Requires an
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already initialized <code>$instance</code> value to work with.</div></li></ul><h2 id="enums" class="section-header">Enums<a href="#enums" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="enum" href="enum.PodCastError.html" title="enum bytemuck::PodCastError">PodCast<wbr>Error</a></div><div class="desc docblock-short">The things that can go wrong when casting between <a href="trait.Pod.html" title="trait bytemuck::Pod"><code>Pod</code></a> data forms.</div></li></ul><h2 id="traits" class="section-header">Traits<a href="#traits" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="trait" href="trait.AnyBitPattern.html" title="trait bytemuck::AnyBitPattern">AnyBit<wbr>Pattern</a></div><div class="desc docblock-short">Marker trait for “plain old data” types that are valid for any bit pattern.</div></li><li><div class="item-name"><a class="trait" href="trait.Contiguous.html" title="trait bytemuck::Contiguous">Contiguous</a></div><div class="desc docblock-short">A trait indicating that:</div></li><li><div class="item-name"><a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a></div><div class="desc docblock-short">Marker trait for “plain old data” types with no uninit (or padding) bytes.</div></li><li><div class="item-name"><a class="trait" href="trait.Pod.html" title="trait bytemuck::Pod">Pod</a></div><div class="desc docblock-short">Marker trait for “plain old data”.</div></li><li><div class="item-name"><a class="trait" href="trait.PodInOption.html" title="trait bytemuck::PodInOption">PodIn<wbr>Option</a></div><div class="desc docblock-short">Trait for types which are <a href="trait.Pod.html" title="trait bytemuck::Pod">Pod</a> when wrapped in
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<a href="https://doc.rust-lang.org/1.84.0/core/option/enum.Option.html" title="enum core::option::Option">Option</a>.</div></li><li><div class="item-name"><a class="trait" href="trait.TransparentWrapper.html" title="trait bytemuck::TransparentWrapper">Transparent<wbr>Wrapper</a></div><div class="desc docblock-short">A trait which indicates that a type is a <code>#[repr(transparent)]</code> wrapper
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around the <code>Inner</code> value.</div></li><li><div class="item-name"><a class="trait" href="trait.Zeroable.html" title="trait bytemuck::Zeroable">Zeroable</a></div><div class="desc docblock-short">Trait for types that can be safely created with
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<a href="https://doc.rust-lang.org/1.84.0/core/mem/fn.zeroed.html" title="fn core::mem::zeroed"><code>zeroed</code></a>.</div></li><li><div class="item-name"><a class="trait" href="trait.ZeroableInOption.html" title="trait bytemuck::ZeroableInOption">Zeroable<wbr>InOption</a></div><div class="desc docblock-short">Trait for types which are <a href="trait.Zeroable.html" title="trait bytemuck::Zeroable">Zeroable</a> when wrapped in
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<a href="https://doc.rust-lang.org/1.84.0/core/option/enum.Option.html" title="enum core::option::Option">Option</a>.</div></li></ul><h2 id="functions" class="section-header">Functions<a href="#functions" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="fn" href="fn.bytes_of.html" title="fn bytemuck::bytes_of">bytes_<wbr>of</a></div><div class="desc docblock-short">Re-interprets <code>&T</code> as <code>&[u8]</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.bytes_of_mut.html" title="fn bytemuck::bytes_of_mut">bytes_<wbr>of_<wbr>mut</a></div><div class="desc docblock-short">Re-interprets <code>&mut T</code> as <code>&mut [u8]</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.cast.html" title="fn bytemuck::cast">cast</a></div><div class="desc docblock-short">Cast <code>A</code> into <code>B</code></div></li><li><div class="item-name"><a class="fn" href="fn.cast_mut.html" title="fn bytemuck::cast_mut">cast_<wbr>mut</a></div><div class="desc docblock-short">Cast <code>&mut A</code> into <code>&mut B</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.cast_ref.html" title="fn bytemuck::cast_ref">cast_<wbr>ref</a></div><div class="desc docblock-short">Cast <code>&A</code> into <code>&B</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.cast_slice.html" title="fn bytemuck::cast_slice">cast_<wbr>slice</a></div><div class="desc docblock-short">Cast <code>&[A]</code> into <code>&[B]</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.cast_slice_mut.html" title="fn bytemuck::cast_slice_mut">cast_<wbr>slice_<wbr>mut</a></div><div class="desc docblock-short">Cast <code>&mut [A]</code> into <code>&mut [B]</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.fill_zeroes.html" title="fn bytemuck::fill_zeroes">fill_<wbr>zeroes</a></div><div class="desc docblock-short">Fill all bytes of <code>slice</code> with zeroes (see <a href="trait.Zeroable.html" title="trait bytemuck::Zeroable"><code>Zeroable</code></a>).</div></li><li><div class="item-name"><a class="fn" href="fn.from_bytes.html" title="fn bytemuck::from_bytes">from_<wbr>bytes</a></div><div class="desc docblock-short">Re-interprets <code>&[u8]</code> as <code>&T</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.from_bytes_mut.html" title="fn bytemuck::from_bytes_mut">from_<wbr>bytes_<wbr>mut</a></div><div class="desc docblock-short">Re-interprets <code>&mut [u8]</code> as <code>&mut T</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.must_cast.html" title="fn bytemuck::must_cast">must_<wbr>cast</a></div><div class="desc docblock-short">Cast <code>A</code> into <code>B</code> if infalliable, or fail to compile.</div></li><li><div class="item-name"><a class="fn" href="fn.must_cast_mut.html" title="fn bytemuck::must_cast_mut">must_<wbr>cast_<wbr>mut</a></div><div class="desc docblock-short">Convert a <code>&mut A</code> into <code>&mut B</code> if infalliable, or fail to compile.</div></li><li><div class="item-name"><a class="fn" href="fn.must_cast_ref.html" title="fn bytemuck::must_cast_ref">must_<wbr>cast_<wbr>ref</a></div><div class="desc docblock-short">Convert <code>&A</code> into <code>&B</code> if infalliable, or fail to compile.</div></li><li><div class="item-name"><a class="fn" href="fn.must_cast_slice.html" title="fn bytemuck::must_cast_slice">must_<wbr>cast_<wbr>slice</a></div><div class="desc docblock-short">Convert <code>&[A]</code> into <code>&[B]</code> (possibly with a change in length) if
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infalliable, or fail to compile.</div></li><li><div class="item-name"><a class="fn" href="fn.must_cast_slice_mut.html" title="fn bytemuck::must_cast_slice_mut">must_<wbr>cast_<wbr>slice_<wbr>mut</a></div><div class="desc docblock-short">Convert <code>&mut [A]</code> into <code>&mut [B]</code> (possibly with a change in length) if
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infalliable, or fail to compile.</div></li><li><div class="item-name"><a class="fn" href="fn.pod_align_to.html" title="fn bytemuck::pod_align_to">pod_<wbr>align_<wbr>to</a></div><div class="desc docblock-short">As <a href="https://doc.rust-lang.org/std/primitive.slice.html#method.align_to"><code>align_to</code></a>,
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but safe because of the <a href="trait.Pod.html" title="trait bytemuck::Pod"><code>Pod</code></a> bound.</div></li><li><div class="item-name"><a class="fn" href="fn.pod_align_to_mut.html" title="fn bytemuck::pod_align_to_mut">pod_<wbr>align_<wbr>to_<wbr>mut</a></div><div class="desc docblock-short">As <a href="https://doc.rust-lang.org/std/primitive.slice.html#method.align_to_mut"><code>align_to_mut</code></a>,
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but safe because of the <a href="trait.Pod.html" title="trait bytemuck::Pod"><code>Pod</code></a> bound.</div></li><li><div class="item-name"><a class="fn" href="fn.pod_read_unaligned.html" title="fn bytemuck::pod_read_unaligned">pod_<wbr>read_<wbr>unaligned</a></div><div class="desc docblock-short">Reads the slice into a <code>T</code> value.</div></li><li><div class="item-name"><a class="fn" href="fn.try_cast.html" title="fn bytemuck::try_cast">try_<wbr>cast</a></div><div class="desc docblock-short">Try to cast <code>A</code> into <code>B</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.try_cast_mut.html" title="fn bytemuck::try_cast_mut">try_<wbr>cast_<wbr>mut</a></div><div class="desc docblock-short">Try to convert a <code>&mut A</code> into <code>&mut B</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.try_cast_ref.html" title="fn bytemuck::try_cast_ref">try_<wbr>cast_<wbr>ref</a></div><div class="desc docblock-short">Try to convert a <code>&A</code> into <code>&B</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.try_cast_slice.html" title="fn bytemuck::try_cast_slice">try_<wbr>cast_<wbr>slice</a></div><div class="desc docblock-short">Try to convert <code>&[A]</code> into <code>&[B]</code> (possibly with a change in length).</div></li><li><div class="item-name"><a class="fn" href="fn.try_cast_slice_mut.html" title="fn bytemuck::try_cast_slice_mut">try_<wbr>cast_<wbr>slice_<wbr>mut</a></div><div class="desc docblock-short">Try to convert <code>&mut [A]</code> into <code>&mut [B]</code> (possibly with a change in
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length).</div></li><li><div class="item-name"><a class="fn" href="fn.try_from_bytes.html" title="fn bytemuck::try_from_bytes">try_<wbr>from_<wbr>bytes</a></div><div class="desc docblock-short">Re-interprets <code>&[u8]</code> as <code>&T</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.try_from_bytes_mut.html" title="fn bytemuck::try_from_bytes_mut">try_<wbr>from_<wbr>bytes_<wbr>mut</a></div><div class="desc docblock-short">Re-interprets <code>&mut [u8]</code> as <code>&mut T</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.try_pod_read_unaligned.html" title="fn bytemuck::try_pod_read_unaligned">try_<wbr>pod_<wbr>read_<wbr>unaligned</a></div><div class="desc docblock-short">Reads from the bytes as if they were a <code>T</code>.</div></li><li><div class="item-name"><a class="fn" href="fn.write_zeroes.html" title="fn bytemuck::write_zeroes">write_<wbr>zeroes</a></div><div class="desc docblock-short">Fill all bytes of <code>target</code> with zeroes (see <a href="trait.Zeroable.html" title="trait bytemuck::Zeroable"><code>Zeroable</code></a>).</div></li></ul><h2 id="derives" class="section-header">Derive Macros<a href="#derives" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="derive" href="derive.AnyBitPattern.html" title="derive bytemuck::AnyBitPattern">AnyBit<wbr>Pattern</a></div><div class="desc docblock-short">Derive the <code>AnyBitPattern</code> trait for a struct</div></li><li><div class="item-name"><a class="derive" href="derive.ByteEq.html" title="derive bytemuck::ByteEq">ByteEq</a></div><div class="desc docblock-short">Derive the <code>PartialEq</code> and <code>Eq</code> trait for a type</div></li><li><div class="item-name"><a class="derive" href="derive.ByteHash.html" title="derive bytemuck::ByteHash">Byte<wbr>Hash</a></div><div class="desc docblock-short">Derive the <code>Hash</code> trait for a type</div></li><li><div class="item-name"><a class="derive" href="derive.CheckedBitPattern.html" title="derive bytemuck::CheckedBitPattern">Checked<wbr>BitPattern</a></div><div class="desc docblock-short">Derive the <code>CheckedBitPattern</code> trait for a struct or enum.</div></li><li><div class="item-name"><a class="derive" href="derive.Contiguous.html" title="derive bytemuck::Contiguous">Contiguous</a></div><div class="desc docblock-short">Derive the <code>Contiguous</code> trait for an enum</div></li><li><div class="item-name"><a class="derive" href="derive.NoUninit.html" title="derive bytemuck::NoUninit">NoUninit</a></div><div class="desc docblock-short">Derive the <code>NoUninit</code> trait for a struct or enum</div></li><li><div class="item-name"><a class="derive" href="derive.Pod.html" title="derive bytemuck::Pod">Pod</a></div><div class="desc docblock-short">Derive the <code>Pod</code> trait for a struct</div></li><li><div class="item-name"><a class="derive" href="derive.TransparentWrapper.html" title="derive bytemuck::TransparentWrapper">Transparent<wbr>Wrapper</a></div><div class="desc docblock-short">Derive the <code>TransparentWrapper</code> trait for a struct</div></li><li><div class="item-name"><a class="derive" href="derive.Zeroable.html" title="derive bytemuck::Zeroable">Zeroable</a></div><div class="desc docblock-short">Derive the <code>Zeroable</code> trait for a type.</div></li></ul></section></div></main></body></html> |