As the subject indicates, I'm trying to find the best way to share data between states in a MSM state machine. My first attempt has been to let each sub-machine and state inherit from a common base class, e.g.: struct MyStateMachine_ : public msm::front::state_machine_def<MyStateMachine_,CommonBaseClass> My idea is to add a reference to some shared data in the base class, making it easy to access the shared data from any state. The shared data reference must be passed to the base class. Questions: 1. Is it possible to pass constructor parameters to the common base class' constructor? I have tried different options without success, it seems that the default constructor with no arguments is the only option. 2. If 1. is not possible, what is the best way to initialize the shared property correctly? For example an easy method to iterate over all defined states? (not only the active ones). I have tried to iterate over all states with get_state_by_id, but this method does not enter sub-machines' states. 3. In general, what is the preferred way of implementing shared data between state classes in Boost.MSM? It would have been natural to store the data in the root state, but I can't see that there is an easy way to get access to the root FSM. (only the "nearest parent" FSM in the hierarchy is passed to the various event handler methods). Regards, Tommy