This can be determined with the token, perhaps supplemented with queries to other objects.
Ok, in this case one easy option would be to make the query within the transition action. Contrary to the entry and exit actions, a transition action does have type-safe access to the triggering event. If other objects need to be queried then these could be accessed from the transition action as well. The data that is gathered in the query could be put into a new event which is passed to simple_state::post_event. The destination state would then define an in_state_reaction triggered by the new event. Or, if you want to make the query after entering the destination state: Repost the event carrying the token in the transition action and define an in-state reaction triggered by the same event. The in-state reaction would then execute the query and store the data in the destination state.
I should have mentioned that in our system this is a general pattern, with different token and data types that need to be responded to differently in different states - this is why it seems that the most reliable and general solution would be to pass the event data into the new state. It's true that this removes type safety, since I now have to dynamic_cast or equivalent in order to get to the actual data, but I'm not terribly worried about this (or, maybe more accurately, I don't see a better alternative).
See above, an alternative is the "transition action posts event that triggers an in-state reaction"-pattern (what a name :-)). With this pattern type-safety is upheld, at the cost of needing to process an additional event, which is probably negligible is your case. Another (IMO minor) problem is that you might need move some of the things that you planned to to in the destination state entry action to the in-state reaction. HTH, -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header.