| <!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="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/bytemuck-1.13.1/src/transparent.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>transparent.rs - source</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 rel="stylesheet" href="../../normalize.css"><link rel="stylesheet" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../ayu.css" disabled><link rel="stylesheet" href="../../dark.css" disabled><link rel="stylesheet" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script defer src="../../source-script.js"></script><script defer src="../../source-files.js"></script><script defer src="../../main.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><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></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../bytemuck/index.html"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></a><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="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use super</span>::<span class="kw-2">*</span>; |
| |
| <span class="doccomment">/// A trait which indicates that a type is a `#[repr(transparent)]` wrapper |
| /// around the `Inner` value. |
| /// |
| /// This allows safely copy transmuting between the `Inner` type and the |
| /// `TransparentWrapper` type. Functions like `wrap_{}` convert from the inner |
| /// type to the wrapper type and `peel_{}` functions do the inverse conversion |
| /// from the wrapper type to the inner type. We deliberately do not call the |
| /// wrapper-removing methods "unwrap" because at this point that word is too |
| /// strongly tied to the Option/ Result methods. |
| /// |
| /// # Safety |
| /// |
| /// The safety contract of `TransparentWrapper` is relatively simple: |
| /// |
| /// For a given `Wrapper` which implements `TransparentWrapper<Inner>`: |
| /// |
| /// 1. `Wrapper` must be a wrapper around `Inner` with an identical data |
| /// representations. This either means that it must be a |
| /// `#[repr(transparent)]` struct which contains a either a field of type |
| /// `Inner` (or a field of some other transparent wrapper for `Inner`) as |
| /// the only non-ZST field. |
| /// |
| /// 2. Any fields *other* than the `Inner` field must be trivially constructable |
| /// ZSTs, for example `PhantomData`, `PhantomPinned`, etc. (When deriving |
| /// `TransparentWrapper` on a type with ZST fields, the ZST fields must be |
| /// [`Zeroable`]). |
| /// |
| /// 3. The `Wrapper` may not impose additional alignment requirements over |
| /// `Inner`. |
| /// - Note: this is currently guaranteed by `repr(transparent)`, but there |
| /// have been discussions of lifting it, so it's stated here explicitly. |
| /// |
| /// 4. All functions on `TransparentWrapper` **may not** be overridden. |
| /// |
| /// ## Caveats |
| /// |
| /// If the wrapper imposes additional constraints upon the inner type which are |
| /// required for safety, it's responsible for ensuring those still hold -- this |
| /// generally requires preventing access to instances of the inner type, as |
| /// implementing `TransparentWrapper<U> for T` means anybody can call |
| /// `T::cast_ref(any_instance_of_u)`. |
| /// |
| /// For example, it would be invalid to implement TransparentWrapper for `str` |
| /// to implement `TransparentWrapper` around `[u8]` because of this. |
| /// |
| /// # Examples |
| /// |
| /// ## Basic |
| /// |
| /// ``` |
| /// use bytemuck::TransparentWrapper; |
| /// # #[derive(Default)] |
| /// # struct SomeStruct(u32); |
| /// |
| /// #[repr(transparent)] |
| /// struct MyWrapper(SomeStruct); |
| /// |
| /// unsafe impl TransparentWrapper<SomeStruct> for MyWrapper {} |
| /// |
| /// // interpret a reference to &SomeStruct as a &MyWrapper |
| /// let thing = SomeStruct::default(); |
| /// let inner_ref: &MyWrapper = MyWrapper::wrap_ref(&thing); |
| /// |
| /// // Works with &mut too. |
| /// let mut mut_thing = SomeStruct::default(); |
| /// let inner_mut: &mut MyWrapper = MyWrapper::wrap_mut(&mut mut_thing); |
| /// |
| /// # let _ = (inner_ref, inner_mut); // silence warnings |
| /// ``` |
| /// |
| /// ## Use with dynamically sized types |
| /// |
| /// ``` |
| /// use bytemuck::TransparentWrapper; |
| /// |
| /// #[repr(transparent)] |
| /// struct Slice<T>([T]); |
| /// |
| /// unsafe impl<T> TransparentWrapper<[T]> for Slice<T> {} |
| /// |
| /// let s = Slice::wrap_ref(&[1u32, 2, 3]); |
| /// assert_eq!(&s.0, &[1, 2, 3]); |
| /// |
| /// let mut buf = [1, 2, 3u8]; |
| /// let sm = Slice::wrap_mut(&mut buf); |
| /// ``` |
| /// |
| /// ## Deriving |
| /// |
| /// When deriving, the non-wrapped fields must uphold all the normal requirements, |
| /// and must also be `Zeroable`. |
| /// |
| </span><span class="attribute">#[cfg_attr(feature = <span class="string">"derive"</span>, doc = <span class="string">"```"</span>)] |
| #[cfg_attr( |
| not(feature = <span class="string">"derive"</span>), |
| doc = <span class="string">"```ignore |
| // This example requires the `derive` feature." |
| </span>)] |
| </span><span class="doccomment">/// use bytemuck::TransparentWrapper; |
| /// use std::marker::PhantomData; |
| /// |
| /// #[derive(TransparentWrapper)] |
| /// #[repr(transparent)] |
| /// #[transparent(usize)] |
| /// struct Wrapper<T: ?Sized>(usize, PhantomData<T>); // PhantomData<T> implements Zeroable for all T |
| /// ``` |
| /// |
| /// Here, an error will occur, because `MyZst` does not implement `Zeroable`. |
| /// |
| </span><span class="attribute">#[cfg_attr(feature = <span class="string">"derive"</span>, doc = <span class="string">"```compile_fail"</span>)] |
| #[cfg_attr( |
| not(feature = <span class="string">"derive"</span>), |
| doc = <span class="string">"```ignore |
| // This example requires the `derive` feature." |
| </span>)] |
| </span><span class="doccomment">/// use bytemuck::TransparentWrapper; |
| /// struct MyZst; |
| /// |
| /// #[derive(TransparentWrapper)] |
| /// #[repr(transparent)] |
| /// #[transparent(usize)] |
| /// struct Wrapper(usize, MyZst); // MyZst does not implement Zeroable |
| /// ``` |
| </span><span class="kw">pub unsafe trait </span>TransparentWrapper<Inner: <span class="question-mark">?</span>Sized> { |
| <span class="doccomment">/// Convert the inner type into the wrapper type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>wrap(s: Inner) -> <span class="self">Self |
| </span><span class="kw">where |
| </span><span class="self">Self</span>: Sized, |
| Inner: Sized, |
| { |
| <span class="comment">// SAFETY: The unsafe contract requires that `Self` and `Inner` have |
| // identical representations. |
| </span><span class="kw">unsafe </span>{ <span class="macro">transmute!</span>(s) } |
| } |
| |
| <span class="doccomment">/// Convert a reference to the inner type into a reference to the wrapper |
| /// type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>wrap_ref(s: <span class="kw-2">&</span>Inner) -> <span class="kw-2">&</span><span class="self">Self </span>{ |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*const </span>Inner>() == size_of::<<span class="kw-2">*const </span><span class="self">Self</span>>()); |
| <span class="comment">// A pointer cast doesn't work here because rustc can't tell that |
| // the vtables match (because of the `?Sized` restriction relaxation). |
| // A `transmute` doesn't work because the sizes are unspecified. |
| // |
| // SAFETY: The unsafe contract requires that these two have |
| // identical representations. |
| </span><span class="kw">let </span>inner_ptr = s <span class="kw">as </span><span class="kw-2">*const </span>Inner; |
| <span class="kw">let </span>wrapper_ptr: <span class="kw-2">*const </span><span class="self">Self </span>= <span class="macro">transmute!</span>(inner_ptr); |
| <span class="kw-2">&*</span>wrapper_ptr |
| } |
| } |
| |
| <span class="doccomment">/// Convert a mutable reference to the inner type into a mutable reference to |
| /// the wrapper type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>wrap_mut(s: <span class="kw-2">&mut </span>Inner) -> <span class="kw-2">&mut </span><span class="self">Self </span>{ |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*mut </span>Inner>() == size_of::<<span class="kw-2">*mut </span><span class="self">Self</span>>()); |
| <span class="comment">// A pointer cast doesn't work here because rustc can't tell that |
| // the vtables match (because of the `?Sized` restriction relaxation). |
| // A `transmute` doesn't work because the sizes are unspecified. |
| // |
| // SAFETY: The unsafe contract requires that these two have |
| // identical representations. |
| </span><span class="kw">let </span>inner_ptr = s <span class="kw">as </span><span class="kw-2">*mut </span>Inner; |
| <span class="kw">let </span>wrapper_ptr: <span class="kw-2">*mut </span><span class="self">Self </span>= <span class="macro">transmute!</span>(inner_ptr); |
| <span class="kw-2">&mut *</span>wrapper_ptr |
| } |
| } |
| |
| <span class="doccomment">/// Convert a slice to the inner type into a slice to the wrapper type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>wrap_slice(s: <span class="kw-2">&</span>[Inner]) -> <span class="kw-2">&</span>[<span class="self">Self</span>] |
| <span class="kw">where |
| </span><span class="self">Self</span>: Sized, |
| Inner: Sized, |
| { |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*const </span>Inner>() == size_of::<<span class="kw-2">*const </span><span class="self">Self</span>>()); |
| <span class="macro">assert!</span>(align_of::<<span class="kw-2">*const </span>Inner>() == align_of::<<span class="kw-2">*const </span><span class="self">Self</span>>()); |
| <span class="comment">// SAFETY: The unsafe contract requires that these two have |
| // identical representations (size and alignment). |
| </span>core::slice::from_raw_parts(s.as_ptr() <span class="kw">as </span><span class="kw-2">*const </span><span class="self">Self</span>, s.len()) |
| } |
| } |
| |
| <span class="doccomment">/// Convert a mutable slice to the inner type into a mutable slice to the |
| /// wrapper type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>wrap_slice_mut(s: <span class="kw-2">&mut </span>[Inner]) -> <span class="kw-2">&mut </span>[<span class="self">Self</span>] |
| <span class="kw">where |
| </span><span class="self">Self</span>: Sized, |
| Inner: Sized, |
| { |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*mut </span>Inner>() == size_of::<<span class="kw-2">*mut </span><span class="self">Self</span>>()); |
| <span class="macro">assert!</span>(align_of::<<span class="kw-2">*mut </span>Inner>() == align_of::<<span class="kw-2">*mut </span><span class="self">Self</span>>()); |
| <span class="comment">// SAFETY: The unsafe contract requires that these two have |
| // identical representations (size and alignment). |
| </span>core::slice::from_raw_parts_mut(s.as_mut_ptr() <span class="kw">as </span><span class="kw-2">*mut </span><span class="self">Self</span>, s.len()) |
| } |
| } |
| |
| <span class="doccomment">/// Convert the wrapper type into the inner type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>peel(s: <span class="self">Self</span>) -> Inner |
| <span class="kw">where |
| </span><span class="self">Self</span>: Sized, |
| Inner: Sized, |
| { |
| <span class="kw">unsafe </span>{ <span class="macro">transmute!</span>(s) } |
| } |
| |
| <span class="doccomment">/// Convert a reference to the wrapper type into a reference to the inner |
| /// type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>peel_ref(s: <span class="kw-2">&</span><span class="self">Self</span>) -> <span class="kw-2">&</span>Inner { |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*const </span>Inner>() == size_of::<<span class="kw-2">*const </span><span class="self">Self</span>>()); |
| <span class="comment">// A pointer cast doesn't work here because rustc can't tell that |
| // the vtables match (because of the `?Sized` restriction relaxation). |
| // A `transmute` doesn't work because the sizes are unspecified. |
| // |
| // SAFETY: The unsafe contract requires that these two have |
| // identical representations. |
| </span><span class="kw">let </span>wrapper_ptr = s <span class="kw">as </span><span class="kw-2">*const </span><span class="self">Self</span>; |
| <span class="kw">let </span>inner_ptr: <span class="kw-2">*const </span>Inner = <span class="macro">transmute!</span>(wrapper_ptr); |
| <span class="kw-2">&*</span>inner_ptr |
| } |
| } |
| |
| <span class="doccomment">/// Convert a mutable reference to the wrapper type into a mutable reference |
| /// to the inner type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>peel_mut(s: <span class="kw-2">&mut </span><span class="self">Self</span>) -> <span class="kw-2">&mut </span>Inner { |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*mut </span>Inner>() == size_of::<<span class="kw-2">*mut </span><span class="self">Self</span>>()); |
| <span class="comment">// A pointer cast doesn't work here because rustc can't tell that |
| // the vtables match (because of the `?Sized` restriction relaxation). |
| // A `transmute` doesn't work because the sizes are unspecified. |
| // |
| // SAFETY: The unsafe contract requires that these two have |
| // identical representations. |
| </span><span class="kw">let </span>wrapper_ptr = s <span class="kw">as </span><span class="kw-2">*mut </span><span class="self">Self</span>; |
| <span class="kw">let </span>inner_ptr: <span class="kw-2">*mut </span>Inner = <span class="macro">transmute!</span>(wrapper_ptr); |
| <span class="kw-2">&mut *</span>inner_ptr |
| } |
| } |
| |
| <span class="doccomment">/// Convert a slice to the wrapped type into a slice to the inner type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>peel_slice(s: <span class="kw-2">&</span>[<span class="self">Self</span>]) -> <span class="kw-2">&</span>[Inner] |
| <span class="kw">where |
| </span><span class="self">Self</span>: Sized, |
| Inner: Sized, |
| { |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*const </span>Inner>() == size_of::<<span class="kw-2">*const </span><span class="self">Self</span>>()); |
| <span class="macro">assert!</span>(align_of::<<span class="kw-2">*const </span>Inner>() == align_of::<<span class="kw-2">*const </span><span class="self">Self</span>>()); |
| <span class="comment">// SAFETY: The unsafe contract requires that these two have |
| // identical representations (size and alignment). |
| </span>core::slice::from_raw_parts(s.as_ptr() <span class="kw">as </span><span class="kw-2">*const </span>Inner, s.len()) |
| } |
| } |
| |
| <span class="doccomment">/// Convert a mutable slice to the wrapped type into a mutable slice to the |
| /// inner type. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>peel_slice_mut(s: <span class="kw-2">&mut </span>[<span class="self">Self</span>]) -> <span class="kw-2">&mut </span>[Inner] |
| <span class="kw">where |
| </span><span class="self">Self</span>: Sized, |
| Inner: Sized, |
| { |
| <span class="kw">unsafe </span>{ |
| <span class="macro">assert!</span>(size_of::<<span class="kw-2">*mut </span>Inner>() == size_of::<<span class="kw-2">*mut </span><span class="self">Self</span>>()); |
| <span class="macro">assert!</span>(align_of::<<span class="kw-2">*mut </span>Inner>() == align_of::<<span class="kw-2">*mut </span><span class="self">Self</span>>()); |
| <span class="comment">// SAFETY: The unsafe contract requires that these two have |
| // identical representations (size and alignment). |
| </span>core::slice::from_raw_parts_mut(s.as_mut_ptr() <span class="kw">as </span><span class="kw-2">*mut </span>Inner, s.len()) |
| } |
| } |
| } |
| |
| <span class="kw">unsafe impl</span><T> TransparentWrapper<T> <span class="kw">for </span>core::num::Wrapping<T> {} |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="bytemuck" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
