David Abrahams wrote:
Sure, if every state whose entry action can fail has a superstate, you can bail out and leave the machine in the superstate. Are you requiring that?
No, this is not a requirement. But, you are right in your observation that the failure of an entry action of an outermost state cannot be handled anywhere. Consequently, the error handling algorithm will not find a suitable reaction in such a situation and bail out by rethrowing the original exception (the state machine is terminated already).
Is that superstate always a reasonable place to end up upon failure?
Well, you don't excatly end up there, right? The superstate (more accurately the outermost unstable state) is only a "container" for reaction(s) to the exception_thrown event. If such a reaction is found and executed it *must* make a transition to another state (sort of a safe haven) or terminate the state machine itself. Only then are we stable again. To answer your question: Yes, I believe so.
FWIW, I don't know what an orthogonal region is, and I don't have time to learn right now, so I'm probably missing a lot.
I don't think you are missing that much. I hope I have managed to convince you that everything works fine for state machines without orthogonal regions. Orthogonal regions do complicate the matter but not by a lot.
If you're still convinced you have everything right,
Yes, now I believe even more so than before our discussion. Regards, Andreas