html" title="Concept InputIterator">InputIterator</a><span class="special">&gt;</span> 
    <span class="identifier">result_type</span> <a class="link" href="optional_last__idp75552224.html#idp83102432-bb"><span class="keyword">operator</span><span class="special">(</span><span class="special">)</span></a><span class="special">(</span><span class="identifier">InputIterator</span><span class="special">,</span> <span class="identifier">InputIterator</span><span class="special">)</span> <span class="keyword">c