[Question] Can you know upfront if an event can be processed?

[diiigle]

The return value of process_event is already nice to determine if an event has been processed or silently dropped.

bool sm::process_event(event)

When working with user interfaces though, you would like to know upfront what events are currently possible (to grey impossible ones out).

Is there a way to iterate over currently possible events?

sm.visit_current_events([](auto& event){ })

or have a way to test specific events without calling the action?

bool sm::can_process_event(event)

The latter could be achieved with same shared context and guards that would block if you are currently in "query mode". I am just wondering if there could be a reusable way of implementing it, without overloading all guards.

Edit: I did some digging and found

sml/include/boost/sml.hpp

Lines 2558 to 2564 in 58536b9

	constexpr bool execute(const TEvent &event, SM &sm, TDeps &deps, TSubs &subs, typename SM::state_t &, Ts &&...) {
	if (call<TEvent, args_t<G, TEvent>, typename SM::logger_t>::execute(g, event, sm, deps, subs)) {
	call<TEvent, args_t<A, TEvent>, typename SM::logger_t>::execute(a, event, sm, deps, subs);
	return true;
	}
	return false;
	}

So an implementation of can_process_event could call this function with another template parameter, that would prevent calling the action a (call<TEvent, args_t<A, TEvent>,), whereas a call through process_event would allow it.