Hi Robert,
I wonder if the library can provide a debugging mode that would provide a helpful default implementation of no_transition that could help identify the unknown transition rather than requiring the user to write something? Such a function might access internal details, perhaps only provided in the said debugging mode, that would be clearer about the source state and event for which no transition was provided than would user-level code.
Right now you only get an assert in debug mode. I also wonder if more would be possible. About the event, sure, it is already done, about the source state, I can't promise anything, but I will have a look at it. If I understand correctly, you would be satisfied with an assert or error message bringing a bit more debug information? Christophe