_index">iunordered_set_index</a> <span class="special">:</span> <span class="keyword">private</span> iunordered_set_index_aux::allocator_holder&lt; MapConfig &gt;,
                             <span class="keyword">public</span> iunordered_set_index_aux::index_t&lt; MapConfig &gt;
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
  <span class="comment">// types</span>
  <span class="keyword">typedef</span> <span class="identifier">index_type</span><span class=