 a function of the <code>boost::hash</code>
values of its elements. Should we need to specify different hash functions for the
elements of a composite key, we can explicitly do so by using the
<a href="../reference/key_extraction.html#composite_key_hash"><code>composite_key_hash</code></a>
utility:
</p>

<blockquote><pre>
<span class=keyword>struct</span> <span class=identifier>tuned_int_hash</span>
<span class=special>{</span>
  <span class=keyword>int</span> <span class=keyword>operator</span><span class=