n><span class=identifier>endl</span><span class=special>;
    </span><span class=keyword>return </span><span class=identifier>os</span><span class=special>;
  </span><span class=special>}</span>
<span class=special>};
</span>
<span class=keyword>struct </span><span class=identifier>name</span><span class=special>{};</span>
<span class=keyword>struct </span><span class=identifier>by_name</span><span class=special>{};</span>
<span class=keyword>struct </span><span class=identifier>age</span><span class=specia