an class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">is_valid</span><span class="special">(</span><span class="identifier">poly</span><span class="special">)</span> <span class="special">?</span> <span class="string">"valid"</span> <span class="special">:</span> <span class="string">"still invalid"</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span>