pan><span class="special">&lt;</span><span class="identifier">construct_from_double</span><span class="special">&gt;&amp;)</span>
            <span class="special">{</span>
              <span class="keyword">return</span> <span class="number">3.141592653589793238462643383279502884e+00</span><span class="special">;</span>
            <span class="special">}</span>
            <span class="keyword">static</span> <span class="keyword">inline</span>  <span class="identifier">T</span> <span class="identifier">g