48 lines
6.6 KiB
HTML
48 lines
6.6 KiB
HTML
<!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="Asserts that the traits support dynamic dispatch (object-safety)."><title>assert_obj_safe in static_assertions - 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="static_assertions" 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="sidebar-items.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 macro"><!--[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><a class="logo-container" href="../static_assertions/index.html"><img src="https://raw.githubusercontent.com/nvzqz/static-assertions-rs/assets/Icon.png" alt=""></a></nav><nav class="sidebar"><div class="sidebar-crate"><a class="logo-container" href="../static_assertions/index.html"><img src="https://raw.githubusercontent.com/nvzqz/static-assertions-rs/assets/Icon.png" alt="logo"></a><h2><a href="../static_assertions/index.html">static_<wbr>assertions</a><span class="version">1.1.0</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">assert_<wbr>obj_<wbr>safe</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><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 static_<wbr>assertions</a></h2></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"><span class="rustdoc-breadcrumbs"><a href="index.html">static_assertions</a></span><h1>Macro <span class="macro">assert_obj_safe</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/static_assertions/assert_obj_safe.rs.html#72-76">Source</a> </span></div><pre class="rust item-decl"><code>macro_rules! assert_obj_safe {
|
||
($($xs:path),+ $(,)?) => { ... };
|
||
}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Asserts that the traits support dynamic dispatch
|
||
(<a href="https://doc.rust-lang.org/book/ch17-02-trait-objects.html#object-safety-is-required-for-trait-objects">object-safety</a>).</p>
|
||
<p>This is useful for when changes are made to a trait that accidentally
|
||
prevent it from being used as an <a href="https://doc.rust-lang.org/book/ch17-02-trait-objects.html#object-safety-is-required-for-trait-objects">object</a>. Such a case would be adding a
|
||
generic method and forgetting to add <code>where Self: Sized</code> after it. If left
|
||
unnoticed, that mistake will affect crate users and break both forward and
|
||
backward compatibility.</p>
|
||
<h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
|
||
<p>When exposing a public API, it’s important that traits that could previously
|
||
use dynamic dispatch can still do so in future compatible crate versions.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">trait </span>MySafeTrait {
|
||
<span class="kw">fn </span>foo(<span class="kw-2">&</span><span class="self">self</span>) -> u32;
|
||
}
|
||
|
||
<span class="macro">assert_obj_safe!</span>(std::fmt::Write, MySafeTrait);</code></pre></div>
|
||
<p>Works with traits that are not in the calling module:</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">mod </span>inner {
|
||
<span class="kw">pub trait </span>BasicTrait {
|
||
<span class="kw">fn </span>bar(<span class="kw-2">&</span><span class="self">self</span>);
|
||
}
|
||
<span class="macro">assert_obj_safe!</span>(BasicTrait);
|
||
}
|
||
|
||
<span class="macro">assert_obj_safe!</span>(inner::BasicTrait);</code></pre></div>
|
||
<p>The following example fails to compile because raw pointers cannot be sent
|
||
between threads safely:</p>
|
||
|
||
<div class="example-wrap compile_fail"><a href="#" class="tooltip" title="This example deliberately fails to compile">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="macro">assert_impl!</span>(<span class="kw-2">*const </span>u8, Send);</code></pre></div>
|
||
<p>The following example fails to compile because generics without
|
||
<code>where Self: Sized</code> are not allowed in <a href="https://doc.rust-lang.org/book/ch17-02-trait-objects.html#object-safety-is-required-for-trait-objects">object-safe</a> trait methods:</p>
|
||
|
||
<div class="example-wrap compile_fail"><a href="#" class="tooltip" title="This example deliberately fails to compile">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="kw">trait </span>MyUnsafeTrait {
|
||
<span class="kw">fn </span>baz<T>(<span class="kw-2">&</span><span class="self">self</span>) -> T;
|
||
}
|
||
|
||
<span class="macro">assert_obj_safe!</span>(MyUnsafeTrait);</code></pre></div>
|
||
<p>When we fix that, the previous code will compile:</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">trait </span>MyUnsafeTrait {
|
||
<span class="kw">fn </span>baz<T>(<span class="kw-2">&</span><span class="self">self</span>) -> T <span class="kw">where </span><span class="self">Self</span>: Sized;
|
||
}
|
||
|
||
<span class="macro">assert_obj_safe!</span>(MyUnsafeTrait);</code></pre></div>
|
||
</div></details></section></div></main></body></html> |