dentifier">is_from</span><span class="special">(</span><span class="identifier">element_type</span> <span class="special">*</span> <span class="identifier">p</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>

    <span class="identifier">element_type</span> <span class="special">*</span> <span class="identifier">construct</span><span class="special">();</span>
    <span class="comment">// other construct() functions</span>
    <span class="keyword">void</s