<code>&amp;self</code>, <a href="trait.FnMut.html"><code>FnMut</code></a> takes <code>&amp;mut self</code> and <a href="trait.FnOnce.html"><code>FnOnce</code></a> takes <code>self</code>. These correspond to the three kinds of
methods that can be invoked on an instance: call-by-reference,
call-by-mutable-reference, and call-by-value. The most common use of these
traits is to act as bounds to higher-level functions that take functions or
closures as arguments.</p>
<p>Taking a <a href="trait.Fn.html"><code>Fn