rtic/2/api/cortex_m/macro.singleton.html
2024-12-06 13:35:18 +00:00

33 lines
No EOL
5.5 KiB
HTML
Raw Permalink Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<!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="Macro to create a mutable reference to a statically allocated value"><title>singleton in cortex_m - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.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-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-b0742ba02757f159.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="cortex_m" data-themes="" data-resource-suffix="" data-rustdoc-version="1.83.0 (90b35a623 2024-11-26)" data-channel="1.83.0" data-search-js="search-f0d225181b97f9a4.js" data-settings-js="settings-805db61a62df4bd2.js" ><script src="../static.files/storage-1d39b6787ed640ff.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-f070b9041d14864c.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-0111fcff984fae8f.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.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></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../cortex_m/index.html">cortex_<wbr>m</a><span class="version">0.7.7</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">singleton</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#notes" title="Notes">Notes</a></li><li><a href="#example" title="Example">Example</a></li></ul></section><div id="rustdoc-modnav"><h2 class="in-crate"><a href="index.html">In crate cortex_<wbr>m</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">cortex_m</a></span><h1>Macro <span class="macro">singleton</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/cortex_m/macros.rs.html#63-91">source</a> </span></div><pre class="rust item-decl"><span class="macro">macro_rules!</span> singleton {
(<span class="macro-nonterminal">$name</span>:ident: <span class="macro-nonterminal">$ty</span>:ty = <span class="macro-nonterminal">$expr</span>:expr) =&gt; { ... };
(: <span class="macro-nonterminal">$ty</span>:ty = <span class="macro-nonterminal">$expr</span>:expr) =&gt; { ... };
}</pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Macro to create a mutable reference to a statically allocated value</p>
<p>This macro returns a value with type <code>Option&lt;&amp;'static mut $ty&gt;</code>. <code>Some($expr)</code> will be returned
the first time the macro is executed; further calls will return <code>None</code>. To avoid <code>unwrap</code>ping a
<code>None</code> variant the caller must ensure that the macro is called from a function thats executed
at most once in the whole lifetime of the program.</p>
<h2 id="notes"><a class="doc-anchor" href="#notes">§</a>Notes</h2>
<p>This macro is unsound on multi core systems.</p>
<p>For debuggability, you can set an explicit name for a singleton. This name only shows up the
the debugger and is not referencable from other code. See example below.</p>
<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>cortex_m::singleton;
<span class="kw">fn </span>main() {
<span class="comment">// OK if `main` is executed only once
</span><span class="kw">let </span>x: <span class="kw-2">&amp;</span><span class="lifetime">'static </span><span class="kw-2">mut </span>bool = <span class="macro">singleton!</span>(: bool = <span class="bool-val">false</span>).unwrap();
<span class="kw">let </span>y = alias();
<span class="comment">// BAD this second call to `alias` will definitively `panic!`
</span><span class="kw">let </span>y_alias = alias();
}
<span class="kw">fn </span>alias() -&gt; <span class="kw-2">&amp;</span><span class="lifetime">'static </span><span class="kw-2">mut </span>bool {
<span class="macro">singleton!</span>(: bool = <span class="bool-val">false</span>).unwrap()
}
<span class="kw">fn </span>singleton_with_name() {
<span class="comment">// A name only for debugging purposes
</span><span class="macro">singleton!</span>(FOO_BUFFER: [u8; <span class="number">1024</span>] = [<span class="number">0u8</span>; <span class="number">1024</span>]);
}</code></pre></div>
</div></details></section></div></main></body></html>