wise</p>
<div class="highlight-c++"><div class="highlight"><pre><span></span><span class="k">struct</span> <span class="n">UnarySquare</span>
<span class="p">{</span>
  <span class="k">typedef</span> <span class="kt">double</span> <span class="n">argument_type</span><span class="p">;</span>
  <span class="k">typedef</span> <span class="kt">double</span> <span class="n">result_type</span><span class="p">;</span>

  <span class="kt">double</span> <span class="nf">operator</span><span class="p">()(</span><span