Re: [Boost-users] statechart: interaction with environment

From: Andreas Huber (ahd6974-spamgroupstrap_at_[hidden])
Date: 2006-01-21 08:19:42

Oliver.Kowalke_at_[hidden] wrote:
> Hello,
> I try to understand how boost::statechart work - so I have some
> questions.
> If the FSM implements a communication protocol how does the FSM
> interact with the environment?
>
> 1. Problem: How to passing callback-functions to the FSM?
> * The callback should be invoked if the FSM is in a certain state
> and some conditions are met.
> * Do I have to pass the callback(s) with an event

That's the usual and often the best way, because this ensures that your 
FSM can transparently interact with different callers (i.e. senders of 
events). Another, less frequently used option is to pass the callback(s) 
to the constructor of the FSM.

> which has to be
> injected to the FSM from outside

With "injected" I assume you mean that the callback is a member of the 
event?

> and store them in a given state?

Right, if you cannot call the callback immediately (e.g. because you 
have to wait for an event from a different sender before calling the 
callback) you usually store it in a state or the FSM object itself.

> 2. Problem: How to pass initialization parameter into the FSM?
> * Some states need to be initialized with parameters (for instance
> host and port in order to create a socket).
> * Do I Have to pass the parameters via injected events?

That's one way. Again, another is to pass those parameters to the FSM 
constructor.

> 3. Problem: How to pass data between several states in an FSM?
> * Same as Problem 2?

Data that must be shared between multiple states is usually put into a 
common outer state or the FSM object itself. For example, see the 
StopWatch example where the elapsedTime_ member inside the Active state 
is available to both the Stopped and Running states.

HTH & Regards,

-- 
Andreas Huber
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