| <!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="Marker trait for “plain old data” types with no uninit (or padding) bytes."><meta name="keywords" content="rust, rustlang, rust-lang, NoUninit"><title>NoUninit in bytemuck - 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 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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="../bytemuck/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">NoUninit</a></h2><div class="sidebar-elems"><section><h3><a href="#foreign-impls">Implementations on Foreign Types</a></h3><ul class="block"><li><a href="#impl-NoUninit-for-NonZeroI128">NonZeroI128</a></li><li><a href="#impl-NoUninit-for-NonZeroI16">NonZeroI16</a></li><li><a href="#impl-NoUninit-for-NonZeroI32">NonZeroI32</a></li><li><a href="#impl-NoUninit-for-NonZeroI64">NonZeroI64</a></li><li><a href="#impl-NoUninit-for-NonZeroI8">NonZeroI8</a></li><li><a href="#impl-NoUninit-for-NonZeroIsize">NonZeroIsize</a></li><li><a href="#impl-NoUninit-for-NonZeroU128">NonZeroU128</a></li><li><a href="#impl-NoUninit-for-NonZeroU16">NonZeroU16</a></li><li><a href="#impl-NoUninit-for-NonZeroU32">NonZeroU32</a></li><li><a href="#impl-NoUninit-for-NonZeroU64">NonZeroU64</a></li><li><a href="#impl-NoUninit-for-NonZeroU8">NonZeroU8</a></li><li><a href="#impl-NoUninit-for-NonZeroUsize">NonZeroUsize</a></li><li><a href="#impl-NoUninit-for-bool">bool</a></li><li><a href="#impl-NoUninit-for-char">char</a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><h2><a href="index.html">In bytemuck</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">Trait <a href="index.html">bytemuck</a>::<wbr><a class="trait" href="#">NoUninit</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 class="srclink" href="../src/bytemuck/no_uninit.rs.html#61">source</a> · <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 trait"><code>pub unsafe trait NoUninit: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Copy.html" title="trait core::marker::Copy">Copy</a> + 'static { }</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Marker trait for “plain old data” types with no uninit (or padding) bytes.</p> |
| <p>The requirements for this is very similar to <a href="trait.Pod.html" title="Pod"><code>Pod</code></a>, |
| except that it doesn’t require that all bit patterns of the type are valid, |
| i.e. it does not require the type to be <a href="trait.Zeroable.html" title="crate::Zeroable"><code>Zeroable</code></a>. |
| This limits what you can do with a type of this kind, but also broadens the |
| included types to things like C-style enums. Notably, you can only cast from |
| <em>immutable</em> references to a <a href="trait.NoUninit.html" title="NoUninit"><code>NoUninit</code></a> type into <em>immutable</em> references of |
| any other type, no casting of mutable references or mutable references to |
| slices etc.</p> |
| <p><a href="trait.Pod.html" title="Pod"><code>Pod</code></a> is a subset of <a href="trait.NoUninit.html" title="NoUninit"><code>NoUninit</code></a>, meaning that any <code>T: Pod</code> is also |
| <a href="trait.NoUninit.html" title="NoUninit"><code>NoUninit</code></a> but any <code>T: NoUninit</code> is not necessarily <a href="trait.Pod.html" title="Pod"><code>Pod</code></a>. If possible, |
| prefer implementing <a href="trait.Pod.html" title="Pod"><code>Pod</code></a> directly. To get more <a href="trait.Pod.html" title="Pod"><code>Pod</code></a>-like functionality |
| for a type that is only <a href="trait.NoUninit.html" title="NoUninit"><code>NoUninit</code></a>, consider also implementing |
| <a href="checked/trait.CheckedBitPattern.html" title="crate::CheckedBitPattern"><code>CheckedBitPattern</code></a>.</p> |
| <h2 id="derive"><a href="#derive">Derive</a></h2> |
| <p>A <code>#[derive(NoUninit)]</code> macro is provided under the <code>derive</code> feature flag |
| which will automatically validate the requirements of this trait and |
| implement the trait for you for both enums and structs. This is the |
| recommended method for implementing the trait, however it’s also possible to |
| do manually. If you implement it manually, you <em>must</em> carefully follow the |
| below safety rules.</p> |
| <h2 id="safety"><a href="#safety">Safety</a></h2> |
| <p>The same as <a href="trait.Pod.html" title="Pod"><code>Pod</code></a> except we disregard the rule about it must |
| allow any bit pattern (i.e. it does not need to be |
| <a href="trait.Zeroable.html" title="crate::Zeroable"><code>Zeroable</code></a>). Still, this is a quite strong guarantee |
| about a type, so <em>be careful</em> whem implementing it manually.</p> |
| <ul> |
| <li>The type must be inhabited (eg: no |
| <a href="https://doc.rust-lang.org/nightly/core/convert/enum.Infallible.html">Infallible</a>).</li> |
| <li>The type must not contain any uninit (or padding) bytes, either in the |
| middle or on the end (eg: no <code>#[repr(C)] struct Foo(u8, u16)</code>, which has |
| padding in the middle, and also no <code>#[repr(C)] struct Foo(u16, u8)</code>, which |
| has padding on the end).</li> |
| <li>Structs need to have all fields also be <code>NoUninit</code>.</li> |
| <li>Structs need to be <code>repr(C)</code> or <code>repr(transparent)</code>. In the case of |
| <code>repr(C)</code>, the <code>packed</code> and <code>align</code> repr modifiers can be used as long as |
| all other rules end up being followed.</li> |
| <li>Enums need to have an explicit <code>#[repr(Int)]</code></li> |
| <li>Enums must have only fieldless variants</li> |
| <li>It is disallowed for types to contain pointer types, <code>Cell</code>, <code>UnsafeCell</code>, |
| atomics, and any other forms of interior mutability.</li> |
| <li>More precisely: A shared reference to the type must allow reads, and |
| <em>only</em> reads. RustBelt’s separation logic is based on the notion that a |
| type is allowed to define a sharing predicate, its own invariant that must |
| hold for shared references, and this predicate is the reasoning that allow |
| it to deal with atomic and cells etc. We require the sharing predicate to |
| be trivial and permit only read-only access.</li> |
| <li>There’s probably more, don’t mess it up (I mean it).</li> |
| </ul> |
| </div></details><h2 id="foreign-impls" class="small-section-header">Implementations on Foreign Types<a href="#foreign-impls" class="anchor"></a></h2><section id="impl-NoUninit-for-char" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#65">source</a><a href="#impl-NoUninit-for-char" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="primitive" href="https://doc.rust-lang.org/nightly/core/primitive.char.html">char</a></h3></section><section id="impl-NoUninit-for-bool" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#67">source</a><a href="#impl-NoUninit-for-bool" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="primitive" href="https://doc.rust-lang.org/nightly/core/primitive.bool.html">bool</a></h3></section><section id="impl-NoUninit-for-NonZeroU8" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#69">source</a><a href="#impl-NoUninit-for-NonZeroU8" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroU8.html" title="struct core::num::nonzero::NonZeroU8">NonZeroU8</a></h3></section><section id="impl-NoUninit-for-NonZeroI8" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#70">source</a><a href="#impl-NoUninit-for-NonZeroI8" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroI8.html" title="struct core::num::nonzero::NonZeroI8">NonZeroI8</a></h3></section><section id="impl-NoUninit-for-NonZeroU16" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#71">source</a><a href="#impl-NoUninit-for-NonZeroU16" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroU16.html" title="struct core::num::nonzero::NonZeroU16">NonZeroU16</a></h3></section><section id="impl-NoUninit-for-NonZeroI16" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#72">source</a><a href="#impl-NoUninit-for-NonZeroI16" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroI16.html" title="struct core::num::nonzero::NonZeroI16">NonZeroI16</a></h3></section><section id="impl-NoUninit-for-NonZeroU32" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#73">source</a><a href="#impl-NoUninit-for-NonZeroU32" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroU32.html" title="struct core::num::nonzero::NonZeroU32">NonZeroU32</a></h3></section><section id="impl-NoUninit-for-NonZeroI32" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#74">source</a><a href="#impl-NoUninit-for-NonZeroI32" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroI32.html" title="struct core::num::nonzero::NonZeroI32">NonZeroI32</a></h3></section><section id="impl-NoUninit-for-NonZeroU64" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#75">source</a><a href="#impl-NoUninit-for-NonZeroU64" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroU64.html" title="struct core::num::nonzero::NonZeroU64">NonZeroU64</a></h3></section><section id="impl-NoUninit-for-NonZeroI64" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#76">source</a><a href="#impl-NoUninit-for-NonZeroI64" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroI64.html" title="struct core::num::nonzero::NonZeroI64">NonZeroI64</a></h3></section><section id="impl-NoUninit-for-NonZeroU128" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#77">source</a><a href="#impl-NoUninit-for-NonZeroU128" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroU128.html" title="struct core::num::nonzero::NonZeroU128">NonZeroU128</a></h3></section><section id="impl-NoUninit-for-NonZeroI128" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#78">source</a><a href="#impl-NoUninit-for-NonZeroI128" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroI128.html" title="struct core::num::nonzero::NonZeroI128">NonZeroI128</a></h3></section><section id="impl-NoUninit-for-NonZeroUsize" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#79">source</a><a href="#impl-NoUninit-for-NonZeroUsize" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroUsize.html" title="struct core::num::nonzero::NonZeroUsize">NonZeroUsize</a></h3></section><section id="impl-NoUninit-for-NonZeroIsize" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#80">source</a><a href="#impl-NoUninit-for-NonZeroIsize" class="anchor"></a><h3 class="code-header">impl <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/num/nonzero/struct.NonZeroIsize.html" title="struct core::num::nonzero::NonZeroIsize">NonZeroIsize</a></h3></section><h2 id="implementors" class="small-section-header">Implementors<a href="#implementors" class="anchor"></a></h2><div id="implementors-list"><section id="impl-NoUninit-for-T" class="impl has-srclink"><a class="srclink rightside" href="../src/bytemuck/no_uninit.rs.html#63">source</a><a href="#impl-NoUninit-for-T" class="anchor"></a><h3 class="code-header">impl<T: <a class="trait" href="trait.Pod.html" title="trait bytemuck::Pod">Pod</a>> <a class="trait" href="trait.NoUninit.html" title="trait bytemuck::NoUninit">NoUninit</a> for T</h3></section></div><script src="../implementors/bytemuck/no_uninit/trait.NoUninit.js" data-ignore-extern-crates="core" async></script></section></div></main><div 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