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Subject: Re: [boost] [msm] nested pseudo exits with same event ending up in no trans in the most outer state machine.
From: Christophe Henry (christophe.j.henry_at_[hidden])
Date: 2010-07-20 05:02:30

Hi Richard,

>Is it not allowed to use derived classes as backends ?.

Actually, I don't know. I mean, I don't know of a C++ rule forbidding
it, but I'm not a language lawyer.
What I know is that this problem used to happen sporadically with eUML
in the 2.0, but only with VC, and in this case, I see it happen also
with g++ 4.4.
I'd say it's a compiler bug but usually, g++ is right so I'm not sure.

>I was not a ware of it. Is it mentioned in the documentation ?

Probably not because I didn't see it happen any more with MSM v2.10.
It used to happen with the 2.0 and only with VC and eUML.

>If only composite state machines can not be derived classes of
>msm:backend than this is fine because I had only one place till now
>which I have changed already.

We are moving inside uncharted territory. All what I can say is that
it used to happen sporadically and only for eUML composites or
substates. I never, in any version, saw it happen with the main fsm.

Let's try to find a way around. Why do you need to use the back-end as
base class? Could you elaborate?
And will the need go away after I implement the previously discussed
feature that you can pass to the back-end concrete substates instead
of default-constructed ones? Something like what Dave suggested:

  player p(/* for the front-end*/ 3, "a",
              backend_args = (
                 init2=Playing("more data"))

If you describe your use case, I'll try to find a solution. It'd not
be the first time I find a way around compiler bugs ;-)


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