 class="special">&amp;</span> key<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre></li>
<li class="listitem"><pre class="literallayout"><span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <a name="idp36252032-bb"></a><span class="keyword">operator</span><span class="special">[</span><span class="special">]</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">key_type</span> <span cla