Re: [Boost-users] [statechart] forward_event()

Subject: Re: [Boost-users] [statechart] forward_event()
From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2009-10-09 11:07:11

Hi

> I have a state [A] with three orthogonal substates [X,Y,Z]. The states [A] 
> and [X] provide custom reactions for an event [E]. If processing event [E] 
> the state machine calls first the custom reaction in [A]. This method 
> returns with forward_event() ; After this the custom reaction in [A] is 
> called again. And then custom reaction in [X] is called.
>
> This is a little cumbersome. Why is the custom reaction in [A] called 
> twice?
>
> And why is the outermost state called first? It would be something easier 
> to work vice versa. First the more "specialized" inner states could do 
> there work and then the "generalized" outer states can do the everything 
> else.

This behavior is as designed, for an in-depth description please see:

<http://www.boost.org/libs/statechart/doc/reference.html#process_event>

Reaction search always starts with an *arbitrary* innermost state and then 
first works its way outward. Only when the outermost state has been reached 
is the next innermost state checked for a suitable reaction. This behavior 
stems form the fact that all reactions defined in outer states are 
"inherited" by their direct and indirect inner states, as mandated by the 
UML standard.

What are you trying to achieve? Maybe I can suggest a more suitable 
implementation.

HTH,

-- 
Andreas Huber
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