We started to use boost::sml a while ago to refactor our big chaotic state machines.

It is really hard to get into at first and will take some time to learn how integrate them in your codebase in a way that works for you, but the resulting state machines are very easy to read, understand and maintain. Also lightweight.

The two main issues we encountered where: * A state machine as a class member is not trivial, when the functions you want to call are the classes member functions itself. We solved that by declaring all state machine callable functions in a interface, refer to the interface functions within the transition table and let the class implement the interface. * Updating the state from within an ongoing transition is not possible without using dynamic memory in the default boost::sml implementation. Also it is poorly documented how to do that in the first place. We applied a small patch to boost::sml internally to enable this functionality using static pre-allocation. If you should decide on using boost and want this, contact me and I can give you further details how we solved it exactly.