        <span class="comment">// destroy is called whenever the last copy of a multi_pass is</span>
        <span class="comment">// destructed (ownership_policy::release() returned true)</span>
        <span class="comment">//</span>
        <span class="comment">//   mp:    is a reference to the whole multi_pass instance</span>
        <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">MultiPass</span><span class="special">