pan> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">D</span> <span class="special">&gt;</span> <a class="link" href="weak_ptr.html#idp56974032-bb"><span class="identifier">lock</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  <span class="keyword">long</span> <a class="link" href="weak_ptr.html#idp56975056-bb"><span class="identifier">use_count</span></a><span class="special">(<