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<p class='location'>Trait FnMut</p><div class="block items"><ul><li><a href="#required-methods">Required Methods</a></li><li><a href="#implementors">Implementors</a></li></ul></div><p class='location'><a href='../index.html'>std</a>::<wbr><a href='index.html'>ops</a></p><script>window.sidebarCurrent = {name: 'FnMut', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script>
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<h1 class='fqn'><span class='in-band'>Trait <a href='../index.html'>std</a>::<wbr><a href='index.html'>ops</a>::<wbr><a class="trait" href=''>FnMut</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'>
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</span><a class='srclink' href='../../src/core/ops.rs.html#2630-2634' title='goto source code'>[src]</a></span></h1>
<pre class='rust trait'><div class="docblock attributes">#[lang = "fn_mut"]
</div>pub trait FnMut<Args>: <a class="trait" href="../../std/ops/trait.FnOnce.html" title="trait std::ops::FnOnce">FnOnce</a><Args> {
extern "rust-call" fn <a href='#tymethod.call_mut' class='fnname'>call_mut</a>(&mut self, args: Args) -> Self::<a class="trait" href="../../std/ops/trait.FnOnce.html" title="trait std::ops::FnOnce">Output</a>;
}</pre><div class='docblock'><p>A version of the call operator that takes a mutable receiver.</p>
<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
<p>Closures that mutably capture variables automatically implement this trait,
which allows them to be invoked.</p>
<pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">x</span> <span class="op">=</span> <span class="number">5</span>;
{
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">square_x</span> <span class="op">=</span> <span class="op">||</span> <span class="ident">x</span> <span class="op">*=</span> <span class="ident">x</span>;
<span class="ident">square_x</span>();
}
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">x</span>, <span class="number">25</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=fn%20main()%20%7B%0Alet%20mut%20x%20%3D%205%3B%0A%7B%0A%20%20%20%20let%20mut%20square_x%20%3D%20%7C%7C%20x%20*%3D%20x%3B%0A%20%20%20%20square_x()%3B%0A%7D%0Aassert_eq!(x%2C%2025)%3B%0A%7D">Run</a></pre>
<p>Closures can also be passed to higher-level functions through a <code>FnMut</code>
parameter (or a <code>FnOnce</code> parameter, which is a supertrait of <code>FnMut</code>).</p>
<pre class="rust rust-example-rendered">
<span class="kw">fn</span> <span class="ident">do_twice</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="kw-2">mut</span> <span class="ident">func</span>: <span class="ident">F</span>)
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnMut</span>()
{
<span class="ident">func</span>();
<span class="ident">func</span>();
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">x</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">1</span>;
{
<span class="kw">let</span> <span class="ident">add_two_to_x</span> <span class="op">=</span> <span class="op">||</span> <span class="ident">x</span> <span class="op">+=</span> <span class="number">2</span>;
<span class="ident">do_twice</span>(<span class="ident">add_two_to_x</span>);
}
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">x</span>, <span class="number">5</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=fn%20main()%20%7B%0Afn%20do_twice%3CF%3E(mut%20func%3A%20F)%0A%20%20%20%20where%20F%3A%20FnMut()%0A%7B%0A%20%20%20%20func()%3B%0A%20%20%20%20func()%3B%0A%7D%0A%0Alet%20mut%20x%3A%20usize%20%3D%201%3B%0A%7B%0A%20%20%20%20let%20add_two_to_x%20%3D%20%7C%7C%20x%20%2B%3D%202%3B%0A%20%20%20%20do_twice(add_two_to_x)%3B%0A%7D%0A%0Aassert_eq!(x%2C%205)%3B%0A%7D">Run</a></pre>
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<h2 id='required-methods'>Required Methods</h2>
<div class='methods'>
<h3 id='tymethod.call_mut' class='method'><span id='call_mut.v' class='invisible'><code>extern "rust-call" fn <a href='#tymethod.call_mut' class='fnname'>call_mut</a>(&mut self, args: Args) -> Self::<a class="trait" href="../../std/ops/trait.FnOnce.html" title="trait std::ops::FnOnce">Output</a></code></span></h3><div class='stability'><div class='stab unstable'><span class=microscope>🔬</span> This is a nightly-only experimental API. (<code>fn_traits </code><a href="https://github.com/rust-lang/rust/issues/29625">#29625</a>)</div></div><div class='docblock'><p>This is called when the call operator is used.</p>
</div></div>
<h2 id='implementors'>Implementors</h2>
<ul class='item-list' id='implementors-list'>
<li><code>impl<'a, A, F> FnMut<A> for &'a mut F <span class="where fmt-newline">where<br> F: <a class="trait" href="../../std/ops/trait.FnMut.html" title="trait std::ops::FnMut">FnMut</a><A> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></code></li>
<li><code>impl<'a, A, F> FnMut<A> for &'a F <span class="where fmt-newline">where<br> F: <a class="trait" href="../../std/ops/trait.Fn.html" title="trait std::ops::Fn">Fn</a><A> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></code></li>
</ul><script type="text/javascript" async
src="../../implementors/core/ops/trait.FnMut.js">
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