<!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 `IndexMut` trait in crate `core`."><meta name="keywords" content="rust, rustlang, rust-lang, IndexMut"><title>core::ops::IndexMut - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc trait"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../core/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a><p class='location'>Trait IndexMut</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.index_mut">index_mut</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>ops</a></p><script>window.sidebarCurrent = {name: 'IndexMut', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><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"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='in-band'>Trait <a href='../index.html'>core</a>::<wbr><a href='index.html'>ops</a>::<wbr><a class="trait" href=''>IndexMut</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../../src/core/ops/index.rs.html#155-159' title='goto source code'>[src]</a></span></h1><div class="docblock type-decl"><pre class='rust trait'><div class="docblock attributes">#[lang = "index_mut"]
</div>pub trait IndexMut<Idx: ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>: <a class="trait" href="../../core/ops/trait.Index.html" title="trait core::ops::Index">Index</a><Idx> {
fn <a href='#tymethod.index_mut' class='fnname'>index_mut</a>(&mut self, index: Idx) -> &mut Self::<a class="type" href="../../core/ops/trait.Index.html#associatedtype.Output" title="type core::ops::Index::Output">Output</a>;
}</pre></div><div class='docblock'><p>Used for indexing operations (<code>container[index]</code>) in mutable contexts.</p>
<p><code>container[index]</code> is actually syntactic sugar for
<code>*container.index_mut(index)</code>, but only when used as a mutable value. If
an immutable value is requested, the <a href="../../std/ops/trait.Index.html"><code>Index</code></a> trait is used instead. This
allows nice things such as <code>v[index] = value</code>.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>A very simple implementation of a <code>Balance</code> struct that has two sides, where
each can be indexed mutably and immutably.</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ops</span>::{<span class="ident">Index</span>,<span class="ident">IndexMut</span>};
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">enum</span> <span class="ident">Side</span> {
<span class="ident">Left</span>,
<span class="ident">Right</span>,
}
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>, <span class="ident">PartialEq</span>)]</span>
<span class="kw">enum</span> <span class="ident">Weight</span> {
<span class="ident">Kilogram</span>(<span class="ident">f32</span>),
<span class="ident">Pound</span>(<span class="ident">f32</span>),
}
<span class="kw">struct</span> <span class="ident">Balance</span> {
<span class="kw">pub</span> <span class="ident">left</span>: <span class="ident">Weight</span>,
<span class="kw">pub</span> <span class="ident">right</span>: <span class="ident">Weight</span>,
}
<span class="kw">impl</span> <span class="ident">Index</span><span class="op"><</span><span class="ident">Side</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Balance</span> {
<span class="kw">type</span> <span class="ident">Output</span> <span class="op">=</span> <span class="ident">Weight</span>;
<span class="kw">fn</span> <span class="ident">index</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>(<span class="kw-2">&</span><span class="lifetime">'a</span> <span class="self">self</span>, <span class="ident">index</span>: <span class="ident">Side</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">Weight</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"Accessing {:?}-side of balance immutably"</span>, <span class="ident">index</span>);
<span class="kw">match</span> <span class="ident">index</span> {
<span class="ident">Side</span>::<span class="ident">Left</span> <span class="op">=></span> <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">left</span>,
<span class="ident">Side</span>::<span class="ident">Right</span> <span class="op">=></span> <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">right</span>,
}
}
}
<span class="kw">impl</span> <span class="ident">IndexMut</span><span class="op"><</span><span class="ident">Side</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Balance</span> {
<span class="kw">fn</span> <span class="ident">index_mut</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>(<span class="kw-2">&</span><span class="lifetime">'a</span> <span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">index</span>: <span class="ident">Side</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="kw-2">mut</span> <span class="ident">Weight</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"Accessing {:?}-side of balance mutably"</span>, <span class="ident">index</span>);
<span class="kw">match</span> <span class="ident">index</span> {
<span class="ident">Side</span>::<span class="ident">Left</span> <span class="op">=></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">left</span>,
<span class="ident">Side</span>::<span class="ident">Right</span> <span class="op">=></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">right</span>,
}
}
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">balance</span> <span class="op">=</span> <span class="ident">Balance</span> {
<span class="ident">right</span>: <span class="ident">Weight</span>::<span class="ident">Kilogram</span>(<span class="number">2.5</span>),
<span class="ident">left</span>: <span class="ident">Weight</span>::<span class="ident">Pound</span>(<span class="number">1.5</span>),
};
<span class="comment">// In this case, `balance[Side::Right]` is sugar for</span>
<span class="comment">// `*balance.index(Side::Right)`, since we are only *reading*</span>
<span class="comment">// `balance[Side::Right]`, not writing it.</span>
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">balance</span>[<span class="ident">Side</span>::<span class="ident">Right</span>], <span class="ident">Weight</span>::<span class="ident">Kilogram</span>(<span class="number">2.5</span>));
<span class="comment">// However, in this case `balance[Side::Left]` is sugar for</span>
<span class="comment">// `*balance.index_mut(Side::Left)`, since we are writing</span>
<span class="comment">// `balance[Side::Left]`.</span>
<span class="ident">balance</span>[<span class="ident">Side</span>::<span class="ident">Left</span>] <span class="op">=</span> <span class="ident">Weight</span>::<span class="ident">Kilogram</span>(<span class="number">3.0</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Aops%3A%3A%7BIndex%2CIndexMut%7D%3B%0A%0A%23%5Bderive(Debug)%5D%0Aenum%20Side%20%7B%0A%20%20%20%20Left%2C%0A%20%20%20%20Right%2C%0A%7D%0A%0A%23%5Bderive(Debug%2C%20PartialEq)%5D%0Aenum%20Weight%20%7B%0A%20%20%20%20Kilogram(f32)%2C%0A%20%20%20%20Pound(f32)%2C%0A%7D%0A%0Astruct%20Balance%20%7B%0A%20%20%20%20pub%20left%3A%20Weight%2C%0A%20%20%20%20pub%20right%3A%20Weight%2C%0A%7D%0A%0Aimpl%20Index%3CSide%3E%20for%20Balance%20%7B%0A%20%20%20%20type%20Output%20%3D%20Weight%3B%0A%0A%20%20%20%20fn%20index%3C'a%3E(%26'a%20self%2C%20index%3A%20Side)%20-%3E%20%26'a%20Weight%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Accessing%20%7B%3A%3F%7D-side%20of%20balance%20immutably%22%2C%20index)%3B%0A%20%20%20%20%20%20%20%20match%20index%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20Side%3A%3ALeft%20%3D%3E%20%26self.left%2C%0A%20%20%20%20%20%20%20%20%20%20%20%20Side%3A%3ARight%20%3D%3E%20%26self.right%2C%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%7D%0A%7D%0A%0Aimpl%20IndexMut%3CSide%3E%20for%20Balance%20%7B%0A%20%20%20%20fn%20index_mut%3C'a%3E(%26'a%20mut%20self%2C%20index%3A%20Side)%20-%3E%20%26'a%20mut%20Weight%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Accessing%20%7B%3A%3F%7D-side%20of%20balance%20mutably%22%2C%20index)%3B%0A%20%20%20%20%20%20%20%20match%20index%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20Side%3A%3ALeft%20%3D%3E%20%26mut%20self.left%2C%0A%20%20%20%20%20%20%20%20%20%20%20%20Side%3A%3ARight%20%3D%3E%20%26mut%20self.right%2C%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%7D%0A%7D%0A%0Alet%20mut%20balance%20%3D%20Balance%20%7B%0A%20%20%20%20right%3A%20Weight%3A%3AKilogram(2.5)%2C%0A%20%20%20%20left%3A%20Weight%3A%3APound(1.5)%2C%0A%7D%3B%0A%0A%2F%2F%20In%20this%20case%2C%20%60balance%5BSide%3A%3ARight%5D%60%20is%20sugar%20for%0A%2F%2F%20%60*balance.index(Side%3A%3ARight)%60%2C%20since%20we%20are%20only%20*reading*%0A%2F%2F%20%60balance%5BSide%3A%3ARight%5D%60%2C%20not%20writing%20it.%0Aassert_eq!(balance%5BSide%3A%3ARight%5D%2C%20Weight%3A%3AKilogram(2.5))%3B%0A%0A%2F%2F%20However%2C%20in%20this%20case%20%60balance%5BSide%3A%3ALeft%5D%60%20is%20sugar%20for%0A%2F%2F%20%60*balance.index_mut(Side%3A%3ALeft)%60%2C%20since%20we%20are%20writing%0A%2F%2F%20%60balance%5BSide%3A%3ALeft%5D%60.%0Abalance%5BSide%3A%3ALeft%5D%20%3D%20Weight%3A%3AKilogram(3.0)%3B%0A%7D">Run</a></pre>
</div>
<h2 id='required-methods' class='small-section-header'>
Required Methods<a href='#required-methods' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='tymethod.index_mut' class='method'><span id='index_mut.v' class='invisible'><code>fn <a href='#tymethod.index_mut' class='fnname'>index_mut</a>(&mut self, index: Idx) -> &mut Self::<a class="type" href="../../core/ops/trait.Index.html#associatedtype.Output" title="type core::ops::Index::Output">Output</a></code></span></h3><div class='docblock'><p>Performs the mutable indexing (<code>container[index]</code>) operation.</p>
</div></div>
<h2 id='implementors' class='small-section-header'>
Implementors<a href='#implementors' class='anchor'></a>
</h2>
<ul class='item-list' id='implementors-list'>
<li><table class='table-display'><tbody><tr><td><code>impl<T, I> IndexMut<I> for [T] <span class="where fmt-newline">where<br> I: <a class="trait" href="../../core/slice/trait.SliceIndex.html" title="trait core::slice::SliceIndex">SliceIndex</a><[T]>, </span></code><td><div class='out-of-band'><a class='srclink' href='../../src/core/slice/mod.rs.html#1953-1960' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl IndexMut<<a class="struct" href="../../core/ops/struct.Range.html" title="struct core::ops::Range">Range</a><usize>> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/str/mod.rs.html#1689-1694' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl IndexMut<<a class="struct" href="../../core/ops/struct.RangeTo.html" title="struct core::ops::RangeTo">RangeTo</a><usize>> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/str/mod.rs.html#1719-1724' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl IndexMut<<a class="struct" href="../../core/ops/struct.RangeFrom.html" title="struct core::ops::RangeFrom">RangeFrom</a><usize>> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/str/mod.rs.html#1749-1754' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl IndexMut<<a class="struct" href="../../core/ops/struct.RangeFull.html" title="struct core::ops::RangeFull">RangeFull</a>> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/str/mod.rs.html#1779-1784' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl IndexMut<<a class="struct" href="../../core/ops/struct.RangeInclusive.html" title="struct core::ops::RangeInclusive">RangeInclusive</a><usize>> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/str/mod.rs.html#1807-1812' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl IndexMut<<a class="struct" href="../../core/ops/struct.RangeToInclusive.html" title="struct core::ops::RangeToInclusive">RangeToInclusive</a><usize>> for str</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/str/mod.rs.html#1814-1819' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
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