</span>
<span class="comment">//- be default constructible if the container constructor requires it</span>
<span class="comment">//- define the key type using "type"</span>
<span class="comment">//- define an operator() taking "const value_type&amp;" and</span>
<span class="comment">//    returning "type" or "const type &amp;"</span>
<span class="keyword">struct</span> <span class="identifier">first_int_is_key</span>
<span class="special">{</span>
   <span class="keyword">typedef</span> <span class="keyword