oach
    taken by Boost.Signals2 is to return a
    <code class="computeroutput"><a class="link" href="../boost/signals2/connection.html" title="Class connection">signals2::connection</a></code> object that enables
    connected/disconnected query, manual disconnection, and an
    automatic disconnection on destruction mode (<code class="computeroutput"><a class="link" href="../boost/signals2/scoped_connection.html" title="Class scoped_connection">signals2::scoped_connection</a></code>).
    In addition, tw