/span> <span class="keyword">typename</span> DefaultT<span class="special">&gt;</span> 
  <a class="link" href="result_of/extract_or_default.html" title="Struct template extract_or_default">result_of::extract_or_default</a><span class="special">&lt;</span> <span class="identifier">T</span><span class="special">,</span> <span class="identifier">DefaultT</span><span class="special">,</span> <span class="identifier">TagT</span> <span class="special">&gt;</span><span class="special">::</span><span class="identi