Re: [boost] [statechart] Completion transitions again.

From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2007-08-29 18:11:06

Hi Leandro

> I saw your email[1] via the gmane web interface (did you Cc me?

Not exactly, I forwarded the message:

To: llucarella_at_[hidden]
Message-ID: <37229.1564.qm_at_[hidden]>

> maybe
> you mail was eaten by my antispam =).

Probably...

> I don't really know how to handle "partial" completion transitions (I
> mean, with guards). But simple completion transitions could be expressed
> something like:
>
> struct B;
> struct A: sc::simple_state< A, Machine >
> {
> typedef sc::completion_transition< B > reactions;
> };
>
> I guess is better to have partial support than no support at all =)

It seems what you want to do with completion transitions can easily be 
achieved by posting an event in the entry action of a state? That is, the 
only additional work you'd have to do in comparison to a library supported 
scenario is to derive from state instead of simple_state and post an event 
in the ctor? A state that automatically posts an event in its entry action 
is useful in other scenarios, please see Dynamic choice points under:

<http://www.boost.org/libs/statechart/doc/rationale.html#Limitations>

I'm considering to add such a class. I'll have to think about the naming and 
the exact interface though.

> Another simple question about statechart: it can handle this?
>
> ,-----------------.
> | S |<--- T
> | |
> o--+--> A --> B <--o |
> | |
> `-----------------´
>
> I want the state machine to start at A, but any other time S is entered,
> I want to start at B. AFAIK this is possible in UML.

Really? A pointer would be appreciated.

> Can I express that
> in boost.statechart?

Not directly, again you could find out which state you want to enter in a 
initial helper state entry action and then post an appropriate event.

> I think I hit an static assertion when trying to do
> that (/usr/include/boost/statechart/simple_state.hpp:885: error: invalid
> application of ‘sizeof’ to incomplete type
> ‘boost::STATIC_ASSERTION_FAILURE<false>’).

You passed mpl::list filled with multiple initial states? If so, then you 
tried to create a state with multiple orthogonal regions:

<http://www.boost.org/libs/statechart/doc/tutorial.html#OrthogonalStates>

--
Andreas Huber
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