ecial">{</span>
        <span class="keyword">return</span> <span class="identifier">result_type</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">value</span><span class="special">(),</span> <span class="identifier">v</span><span class="special">.</span><span class="identifier">index</span><span class="special">());</span>
    <span class="special">}</span>
<span class="special">};</span>

<span class="keyword">int</span> <span class