>Advanced features of Boost.MultiIndex key
extractors</a></h2>

<p>
The <a href="../reference/key_extraction.html#key_extractors"><code>Key Extractor</code></a>
concept allows the same object to extract keys from several different types,
possibly through suitably defined overloads of <code>operator()</code>:
</p>

<blockquote><pre>
<span class=comment>// example of a name extractor from employee and employee *</span>
<span class=keyword>struct</span> <span class=identifier>name_extractor</span>
<span class=