Re: [Boost-users] [statechart] Getting state information into themachine

From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2008-03-06 15:01:05

Hi

> Here is an simple example: Each session object of the server has two
> states:
> signed-off and authorized. Receiving a login event leads to a transition
> to
> the authorized state. Thats pretty easy. But the login data (stored in the
> login event) got lost. I can hold this data in the state machine itself
> (outermost_context()). Or I can use a pseudo event to forward this data to
> the authorized state. But I'm looking for a nifty way to avoid this
> overhead.

Your observations are correct. Provided that you absolutely want to 
transition when such an event arrives, then these are currently the only 
ways to make the event available to the destination state. Which way is best 
depends on your situation but in your example I'd probably simply post the 
incoming event and have it picked up with an in-state reaction in the 
destination state.

> I like this concept of state-local storage very much. But I'm not
> shure about how to use it.

Maybe you've noticed the existence of 
BOOST_STATECHART_RELAX_TRANSITION_CONTEXT? Currently, this doesn't help you. 
However, one way to solve your problem would be to generalize the relaxing 
concept, so that you can specify any function that happens to accept the 
right type of event and also is a member of any state in the source or 
destination configuration. I've tried to implement this before, but 
abandoned the idea because it makes at lot of heavily templated code much 
more complex. Maybe I'll try again but don't count on getting this feature 
soon!

HTH,

-- 
Andreas Huber
When replying by private email, please remove the words spam and trap
from the address shown in the header.