ass="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span>           <span class="comment">// reference for</span>
            <span class="identifier">boost</span><span class="special">::</span><span class="identifier">add_reference</span><span class="special">&lt;</span>       <span class="comment">// abstract type.</span>
                <span class="identifier">abstract</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="keyw