/span>

   <span class="keyword">bool</span> <span class="identifier">moved</span><span class="special">()</span> <span class="keyword">const</span> <span class="comment">//Observer</span>
   <span class="special">{</span>  <span class="keyword">return</span> <span class="special">!</span><span class="identifier">value_</span><span class="special">;</span> <span class="special">}</span>

   <span class="keyword">int</span> <span class="identifier">value</span><span class="special">()</span> <span class="key