tifier">demo</span>
<span class="special">{</span>
    <span class="keyword">struct</span> <span class="identifier">plus</span>
    <span class="special">{</span>
        <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">&gt;</span>
        <span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span>

        <span class="keyword">template</span> <sp