umber">2</span>);</pre>
<p>Taking a <a href="trait.FnMut.html"><code>FnMut</code></a> as a parameter:</p>

<pre class="rust rust-example-rendered">
<span class="kw">fn</span> <span class="ident">do_twice</span><span class="op">&lt;</span><span class="ident">F</span><span class="op">&gt;</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"