pan class="identifier">value_type</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Combiner<span class="special">&gt;</span> 
    <a class="link" href="map.html" title="Class template map">map</a><span class="special">&lt;</span> <span class="identifier">DomainT</span><span class="special">,</span> <span class="identifier">CodomainT</span><span cl