tifier>T</span><span class=special>&amp;);</span>
<span class=special>};</span>
</pre></blockquote>

<p>
The table below lists the appropriate key extractors to be used for
different pointer and reference wrapper types based on <code>T</code>, for
each of its members.
</p>

<p align="center">
<table cellspacing="0">
  <caption><b>Use cases for Boost.MultiIndex key extractors.</b></caption>
<tr>
  <th>element type</th>
  <th>&nbsp;key&nbsp;</th>
  <th>key extractor</th>
  <th>applicable to<br><code>const</co