Re: [Boost-users] [StateChart] How to pass arguments to a state constructor when doing state transition?

Subject: Re: [Boost-users] [StateChart] How to pass arguments to a state constructor when doing state transition?
From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2011-03-22 14:21:07

Hi

> I have a state like this, which has two parameters in it's constructor
> except the ctx.
> I want to know how to pass these two arguments to the constructor,  when 
> do
> state transition?
> I have tried this:
> transit< RepeatedPlayingState , 1, 2>();
>
> But it cause compiling error? How to do this? I want to pass something to 
> a
> new entered state.

Short answer: By design you can't. The reasons are as follows:

- In general, a transition must be able to enter multiple states at once 
(for the case when there are nested and/or orthogonal states). If you were 
able to pass arguments to transit like you ask then to what state 
constructors are the arguments forwarded? To just the first entered, all of 
them, or just a few select ones?
- Moreover, the same state can be the target of multiple different 
transitions. If just one of those transitions wanted to pass arguments, then 
all other incoming transitions would be forced to pass the same arguments 
too.

So, for the general case passing arguments to transit would become 
unworkable very quickly. However, you can use 
simple_state::triggering_event() to get the triggering event inside the 
state constructor. Note: The states that do so must derive from state 
instead of simple_state.

HTH & Regards,

-- 
Andreas Huber
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