How to use Boost.MSM is_flag_active inside on_entry?

Question

I would like to use is_flag_active() function inside one of my state's on_entry template function:

struct StBladeDown : public msm::front::state<> {
    template<class Event, class FSM>
    void on_entry(Event const& event, FSM& fsm) {
        if(fsm.is_flag_active<FlagMaster>()) { // ERROR
            // doSomeThing();
        }
    }
};

However I got the following compile error:

StOk.hpp: In member function 'void mr::mrd::amfo::StOk_::StBladeDown::on_entry(const Event&, FSM&)':
StOk.hpp:78: error: expected primary-expression before '>' token
StOk.hpp:78: error: expected primary-expression before ')' token

However outside of the state machine, I mean if I first declare a state machine, I can use the is_flag_active:

StAMFODirector backEnd;
backEnd.start();
processEvent(backEnd,EvBladeDown());
processEvent(backEnd,EvMaster());
if(backEnd.is_flag_active<FlagMaster>()){ // OK
    _LOG_DEBUG("Flag Master active");
}

If I use the front_end's is_flag_ I get compiler error again (no such function in msm::back::state_machine).

Any idea how to use is_flag_active together with on_entry? Or if it is not possible are there any alternatives?

Thanks for any help, Gabor

Answer 1

Try this:

struct StBladeDown : public msm::front::state<> {
    template<class Event, class FSM>
    void on_entry(Event const& event, FSM& fsm) {
        if (fsm.template is_flag_active<FlagMaster>()) {
            // doSomeThing();
        }
    }
};

Note the addition of the template keyword. See this FAQ for information about why it's necessary in this context: What is the ->template, .template and ::template syntax about?