 template class <code class="computeroutput"><a class="link" href="reference/is_void.html" title="is_void">is_void</a></code>,
      and provide a full-specialization when <code class="computeroutput"><span class="identifier">T</span></code>
      is <code class="computeroutput"><span class="keyword">void</span></code>. While full specialization
      of a template class is an important technique, sometimes we need a solution
      that is halfway between a fully generic solution, and a full specialization.