 class="identifier">C</span> <span class="special">&amp;</span> iterable<span class="special">,</span> <span class="identifier">metadata_type</span> meta <span class="special">=</span> <span class="special">{</span><span class="special">}</span><span class="special">,</span> 
           <span class="identifier">allocator_type</span> alloc <span class="special">=</span> <span class="special">{</span><span class="special">}</span><span class="special">)</span><span class="special">;</span></pre>Construct axis