<span class="identifier">enable_if_c</span><span class="special">&lt;</span> <span class="identifier">is_base_and_derived</span><span class="special">&lt;</span> <a class="link" href="sink_factory.html" title="Struct template sink_factory">sink_factory</a><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">FactoryT</span><span class="special">::</span><span class="identifier">char_type</span> <span class="special">&gt;</span><span class="special">,</span> <span c