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

From: Leandro Lucarella (llucarella_at_[hidden])
Date: 2007-08-30 11:06:02

> Hi Leandro

Hi

>> 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...

It was a problem with my ISP, if it's not much trouble, please 
Cc/forward me to luca at integratech dyndns org. Thanks!

>> 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>

Yes, I know I could do that, but I have to create a dummy event and it 
looks like a little dirty to me.

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

Great! What about the other idea? I'm sorry about the lame format, my 
MUA was messing my ASCII-art =P. Here it is again, I hope this time is 
more readable:

struct ev: sc::event< ev > {};
struct B;
struct C;
struct A: sc::simple_state< A, Machine >
{
     typedef mpl::list<
             sc::completion_transition< >,
             sc::custom_reaction< ev >
         > reactions;
     sc::result react(const completion_event&)
     {
         if (guard)
             return transit< B >();
         return discard_event();
     }
     sc::result react(const ev&)
     {
         if (!guard)
             return transit< C >();
         return discard_event();
     }
};

>> Another simple question about statechart: it can handle this?
>>
>> ,-----------------.
>> | S |<--- T
>> | |
>> o--+--> A --> B <--o |
>> | |
>> `-----------------´

Same here. What I wanted to show was:

     ,-------------------.  z
     | S                 |<--- T
   w |       x       y   |
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.

Well, it's not exactly the same but in the presentation[1] linked from 
boost.statechart web page is an example (page 6). In the example is not 
the initial pseudostate which goes to the inner state.

>> 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.

Ok, again this is not very pretty, but I didn't figured this out for 
this case, I've tried it and it worked, so thanks :)

>> 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> 

No, I wasn't using orthogonal regions. I tried to reproduce the error in 
a smaller example but I couldn't. I attach the example anyways because I 
hit another error. I'll try to reproduce the previous problem and post 
it later.

TIA

-- 
Leandro Lucarella
Integratech S.A.
4571-5252