gistfile1.cpp

#include <iostream>

struct event_on {};
struct event_off {};

template<class TEvent>
struct ihandle
{
	virtual void handle(TEvent event) = 0;
};

template<class TState>
struct state_machine
{
	template<class TEvent>
	void handle(const TEvent &event)
	{ state->handle(event); }


	TState *state;
};

struct state_light
	: public ihandle<event_on>
	, public ihandle<event_off>
{};

struct state_light_on : public state_light
{
	virtual void handle(event_on event)
	{ std::cout << "light is already on" << std::endl; }

	virtual void handle(event_off event)
	{ std::cout << "switch to off" << std::endl; }
};

struct state_light_off : public state_light
{
	virtual void handle(event_on event)
	{ std::cout << "switch to on" << std::endl; }

	virtual void handle(event_off event)
	{ std::cout << "light is already off" << std::endl; }
};

int main()
{
	state_light_on slon;
	state_light_off sloff;
	
	state_machine<state_light> sm;
	sm.state = &slon;
	sm.handle(event_on());
	sm.handle(event_off());

	sm.state = &sloff;
	sm.handle(event_on());
	sm.handle(event_off());
}

Der Compiler sucht erst die function in dem Fall "handle" auf struct state_light. Jetzt erkennt er, dass es den zweimal gibt, einmal
in base class ihandle<event_on> und einmal in ihandle<event_off>. Da kommt er schon durcheinander. Der eigentliche overload würde später
passieren, aber soweit kommt er nicht.

github ate my template parameters :-( second try
...
einmal in base class ihandle&lt:event_on> und einmal in ihandle&lt:event_off>
...

grrr ....