omment">// exception.</span>
    <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">decay</span><span class="special">&lt;</span> <span class="identifier">Fn</span> <span class="special">&gt;::</span><span class="ident