mplate</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Polygon</span><span class="special">,</span> <span class="special">&gt;</span>
<span class="identifier">ring_return_type</span><span class="special">&lt;</span><span class="identifier">Polygon</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">exterior_ring</span><span class="special">(</span><span class="identifier">Polygon</span> <span class="spec