er">value_as</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Axis</span> <span class="special">&amp;</span><span class="special">,</span> <span class="identifier">real_index_type</span><span class="special">)</span><span class="special">;</span>
        <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Axis<span class="special">,</span> <span class="keyword">typename</span> U<span class="special">&g