s=identifier>ActionT</span><span class=special>&gt;
        </span><span class=identifier>action</span><span class=special>&lt;</span><span class=identifier>DerivedT</span><span class=special>, </span><span class=identifier>ActionT</span><span class=special>&gt;
        </span><span class=keyword>operator</span><span class=special>[](</span><span class=identifier>ActionT </span><span class=keyword>const</span><span class=special>&amp; </span><span class=identifier>actor</span><span class=special>) </span><s