s="identifier">Key</span><span class="special">,</span> <span class="identifier">T</span> <span class="special">&gt;</span> <span class="special">&amp;</span> <a class="link" href="flat_map.html#idp36256400-bb"><span class="keyword">operator</span><span class="special">=</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">flat_map</span><span class="special">&lt;</span> <span class="identifier">Key</span><span class="special">,</span> <span class="identifier">