-the-call-operator-on-function-objects" title="Permalink to this headline">¶</a></h2>
<p>Mutable function objects are not prohibited, they just need to be explicit by
using the adaptor <a class="reference internal" href="../../include/boost/hof/mutable.html"><span class="doc">mutable</span></a>. The main reason for this, is that it can lead to
many suprising behaviours. Many times function objects are copied by value
everywhere. For example,</p>
<div class="highlight-cpp"><div class="highlight"><pre><span>