use some</span>
<span class="comment">// specific types. One could also take Value as template parameter and access</span>
<span class="comment">// first_type and second_type members, etc.</span>
<span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">First</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Second</span><span class="special">&gt;</span>
<span class="keyword">struct<