ad, the signal may call into
      a partially destroyed object.
    </p>
<p>We solve this problem by requiring that tracked objects be
      managed by <code class="computeroutput">shared_ptr</code>.  Slots keep a
      <code class="computeroutput">weak_ptr</code> to every object the slot depends
      on.  Connections to a slot are disconnected when any of its tracked
      <code class="computeroutput">weak_ptr</code>s expire.  Additionally, signals
      create their own temporary <code class="computerou