e</span> <span class="identifier">demo</span>
<span class="special">{</span>
    <span class="keyword">struct</span> <span class="identifier">foo</span>
    <span class="special">{</span>
        <span class="keyword">typedef</span> <span class="keyword">int</span> <span class="identifier">result_type</span><span class="special">;</span>

        <span class="identifier">result_type</span> <span class="keyword">operator</span><span class="special">()()</span> <span class="keyword">const</span>
        <span