Re: [boost] [review] FSM Second Call for Reviews

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2008-08-31 12:55:45

On Sun, 2008-08-31 at 15:28 +0200, Thomas Klimpel wrote:
> Andrey Semashev wrote:
> > Not exactly. You don't have to override the transit handler unless you
> > want to define some non-trivial transition logic. If you stick to the
> > same degree of functionality that TMP provides (IOW, no runtime
> > conditions for the transition to take place), then you can use the
> > fsm::transition class as a direct replacement for the row template in
> > the TMP approach.
> > 
> > If you have to decide when and which state to transit to in runtime,
> > then yes, you have to define your custom transition rule.
> 
> But how can I specify the "transition action", if not by overriding the "transit" method?

As I said, if you need some non-trivial (i.e. something more complex
than a mere call to switch_to), you have to implement the transit
handler. Otherwise, you don't have to do that and you get precisely what
the TMP solution provides. 

> And even if I override the "transit" method, how should I handle the fact that the event will still be delivered to the target state?

Process the event. Every event passed to the state machine must be
processed in some way - either in one of the on_process handlers, or in
the unexpected events handler. You cannot cancel the event delivery
because the machine has to return something from the FSM's process
method.