ation is quite logical: as the hash value of a composite
key depends on all of its elements, it is impossible to calculate it from
partial information.
</p>

<h2><a name="key">C++17 terse key specification syntax</a></h2>

<p>
C++17 introduces the declaration of <code>auto</code> template parameters, which can be
taken advantage of to eliminate some redundancy in the specification of Boost.MultiIndex
predefined key extractors. For instance, instead of the classical:
</p>

<blockquote><pre>
<span class=keywo