identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">last_name</span> <span class="special">=</span> <span class="string">""</span>
        <span class="special">)</span>
        <span class="special">:</span> <span class="identifier">first_name</span><span class="special">(</span><span class="identifier">first_name</span><span class="special">)</span>
        <span class="spe