nHandling">Exception
  handling</a> chapter in the Tutorial.</p>

  <h3>Two stage exit</h3>

  <p>An exit action can be implemented by adding a destructor to a state. Due
  to the nature of destructors, there are two disadvantages to this
  approach:</p>

  <ul>
    <li>Since C++ destructors should virtually never throw, one cannot simply
    propagate an exception from an exit action as one does when any of the
    other actions fails</li>

    <li>When a <code>state_machine&lt;&gt;</code> object is destru