Re: [Boost-users] [statechart] context sensitive history

From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2007-12-01 06:14:57

Hi Chris

> I have the following requirement:  States A and B, where B has two
> substates
> B1 and B2.  When transition occurs from B to A, and then from A
> back to B,
> under some conditions it is desired for B1 to be the initial
> substate, while
> in others we would like the substate to be chosen based on B's
> shallow
> history.
>
> Is there a concise way to obtain this behavior from the statecharts
> library?

Yep, you'd make B1 a shallow-history inner initial state, as follows:

struct B : sc::simple_state< B, Machine,
  mpl::list< sc::shallow_history< B1 > >, sc::has_shallow_history >
{
  // ...
};

(Note the need to wrap the history state into an mpl::list, see
<http://www.boost.org/libs/statechart/doc/tutorial.html#History>)

Now, whenever you need B1 to be the inner initial state (regardless
of previous history), you simply clear history information before
transitioning to B, as documented here:

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

There's now also a FAQ item: 
<http://www.boost-consulting.com/boost/libs/statechart/doc/faq.html#DisableHistory>

HTH,

-- 
Andreas Huber
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