178 lines
No EOL
7.5 KiB
HTML
178 lines
No EOL
7.5 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="API documentation for the Rust `default` mod in crate `bitflags`.">
|
||
<meta name="keywords" content="rust, rustlang, rust-lang, default">
|
||
|
||
<title>bitflags::__core::default - Rust</title>
|
||
|
||
<link rel="stylesheet" type="text/css" href="../../../rustdoc.css">
|
||
<link rel="stylesheet" type="text/css" href="../../../main.css">
|
||
|
||
|
||
|
||
|
||
</head>
|
||
<body class="rustdoc">
|
||
<!--[if lte IE 8]>
|
||
<div class="warning">
|
||
This old browser is unsupported and will most likely display funky
|
||
things.
|
||
</div>
|
||
<![endif]-->
|
||
|
||
|
||
|
||
<nav class="sidebar">
|
||
|
||
<p class='location'><a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a></p><script>window.sidebarCurrent = {name: 'default', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script>
|
||
</nav>
|
||
|
||
<nav class="sub">
|
||
<form class="search-form js-only">
|
||
<div class="search-container">
|
||
<input class="search-input" name="search"
|
||
autocomplete="off"
|
||
placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
|
||
type="search">
|
||
</div>
|
||
</form>
|
||
</nav>
|
||
|
||
<section id='main' class="content mod">
|
||
<h1 class='fqn'><span class='in-band'>Module <a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a class='mod' href=''>default</a></span><span class='out-of-band'><span id='render-detail'>
|
||
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
|
||
[<span class='inner'>−</span>]
|
||
</a>
|
||
</span><a id='src-22549' class='srclink' href='https://doc.rust-lang.org/nightly/core/default/index.html?gotosrc=22549' title='goto source code'>[src]</a></span></h1>
|
||
<div class='docblock'><p>The <code>Default</code> trait for types which may have meaningful default values.</p>
|
||
|
||
<p>Sometimes, you want to fall back to some kind of default value, and
|
||
don't particularly care what it is. This comes up often with <code>struct</code>s
|
||
that define a set of options:</p>
|
||
|
||
<pre class='rust rust-example-rendered'>
|
||
<span class='kw'>struct</span> <span class='ident'>SomeOptions</span> {
|
||
<span class='ident'>foo</span>: <span class='ident'>i32</span>,
|
||
<span class='ident'>bar</span>: <span class='ident'>f32</span>,
|
||
}</pre>
|
||
|
||
<p>How can we define some default values? You can use <code>Default</code>:</p>
|
||
|
||
<pre class='rust rust-example-rendered'>
|
||
<span class='attribute'>#[<span class='ident'>derive</span>(<span class='ident'>Default</span>)]</span>
|
||
<span class='kw'>struct</span> <span class='ident'>SomeOptions</span> {
|
||
<span class='ident'>foo</span>: <span class='ident'>i32</span>,
|
||
<span class='ident'>bar</span>: <span class='ident'>f32</span>,
|
||
}
|
||
|
||
|
||
<span class='kw'>fn</span> <span class='ident'>main</span>() {
|
||
<span class='kw'>let</span> <span class='ident'>options</span>: <span class='ident'>SomeOptions</span> <span class='op'>=</span> <span class='ident'>Default</span>::<span class='ident'>default</span>();
|
||
}</pre>
|
||
|
||
<p>Now, you get all of the default values. Rust implements <code>Default</code> for various primitives types.
|
||
If you have your own type, you need to implement <code>Default</code> yourself:</p>
|
||
|
||
<pre class='rust rust-example-rendered'>
|
||
<span class='kw'>enum</span> <span class='ident'>Kind</span> {
|
||
<span class='ident'>A</span>,
|
||
<span class='ident'>B</span>,
|
||
<span class='ident'>C</span>,
|
||
}
|
||
|
||
<span class='kw'>impl</span> <span class='ident'>Default</span> <span class='kw'>for</span> <span class='ident'>Kind</span> {
|
||
<span class='kw'>fn</span> <span class='ident'>default</span>() <span class='op'>-></span> <span class='ident'>Kind</span> { <span class='ident'>Kind</span>::<span class='ident'>A</span> }
|
||
}
|
||
|
||
<span class='attribute'>#[<span class='ident'>derive</span>(<span class='ident'>Default</span>)]</span>
|
||
<span class='kw'>struct</span> <span class='ident'>SomeOptions</span> {
|
||
<span class='ident'>foo</span>: <span class='ident'>i32</span>,
|
||
<span class='ident'>bar</span>: <span class='ident'>f32</span>,
|
||
<span class='ident'>baz</span>: <span class='ident'>Kind</span>,
|
||
}
|
||
|
||
|
||
<span class='kw'>fn</span> <span class='ident'>main</span>() {
|
||
<span class='kw'>let</span> <span class='ident'>options</span>: <span class='ident'>SomeOptions</span> <span class='op'>=</span> <span class='ident'>Default</span>::<span class='ident'>default</span>();
|
||
}</pre>
|
||
|
||
<p>If you want to override a particular option, but still retain the other defaults:</p>
|
||
|
||
<pre class='rust rust-example-rendered'>
|
||
<span class='kw'>fn</span> <span class='ident'>main</span>() {
|
||
<span class='kw'>let</span> <span class='ident'>options</span> <span class='op'>=</span> <span class='ident'>SomeOptions</span> { <span class='ident'>foo</span>: <span class='number'>42</span>, ..<span class='ident'>Default</span>::<span class='ident'>default</span>() };
|
||
}</pre>
|
||
</div><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class='trait' href='trait.Default.html'
|
||
title='bitflags::__core::default::Default'>Default</a></td>
|
||
<td class='docblock short'>
|
||
<p>A trait for giving a type a useful default value.</p>
|
||
</td>
|
||
</tr></table></section>
|
||
<section id='search' class="content hidden"></section>
|
||
|
||
<section class="footer"></section>
|
||
|
||
<aside id="help" class="hidden">
|
||
<div>
|
||
<h1 class="hidden">Help</h1>
|
||
|
||
<div class="shortcuts">
|
||
<h2>Keyboard Shortcuts</h2>
|
||
|
||
<dl>
|
||
<dt>?</dt>
|
||
<dd>Show this help dialog</dd>
|
||
<dt>S</dt>
|
||
<dd>Focus the search field</dd>
|
||
<dt>⇤</dt>
|
||
<dd>Move up in search results</dd>
|
||
<dt>⇥</dt>
|
||
<dd>Move down in search results</dd>
|
||
<dt>⏎</dt>
|
||
<dd>Go to active search result</dd>
|
||
</dl>
|
||
</div>
|
||
|
||
<div class="infos">
|
||
<h2>Search Tricks</h2>
|
||
|
||
<p>
|
||
Prefix searches with a type followed by a colon (e.g.
|
||
<code>fn:</code>) to restrict the search to a given type.
|
||
</p>
|
||
|
||
<p>
|
||
Accepted types are: <code>fn</code>, <code>mod</code>,
|
||
<code>struct</code>, <code>enum</code>,
|
||
<code>trait</code>, <code>type</code>, <code>macro</code>,
|
||
and <code>const</code>.
|
||
</p>
|
||
|
||
<p>
|
||
Search functions by type signature (e.g.
|
||
<code>vec -> usize</code> or <code>* -> vec</code>)
|
||
</p>
|
||
</div>
|
||
</div>
|
||
</aside>
|
||
|
||
|
||
|
||
<script>
|
||
window.rootPath = "../../../";
|
||
window.currentCrate = "bitflags";
|
||
window.playgroundUrl = "";
|
||
</script>
|
||
<script src="../../../jquery.js"></script>
|
||
<script src="../../../main.js"></script>
|
||
|
||
<script defer src="../../../search-index.js"></script>
|
||
</body>
|
||
</html> |