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| #include <iostream>
struct BaseInterface { virtual ~BaseInterface()= 0; };
inline
BaseInterface::~BaseInterface()= default;
// Tags
struct A; struct B; struct C;
template< typename... Tags >
struct Interface;
template<>
template< typename Car, typename... Cdr >
struct Interface< Car, Cdr... >:
virtual public BaseInterface,
virtual public Interface< Car >,
virtual public Interface< Cdr... > {
};
// Interfaces
template<>
struct Interface< A >:
virtual public BaseInterface {
virtual void a()= 0;
};
template<>
struct Interface< B >:
virtual public BaseInterface {
virtual void b()= 0;
};
template<>
struct Interface< C >:
virtual public BaseInterface {
virtual void c()= 0;
};
template< typename _Who, typename... What >
struct Implementation;
template< typename _Who, typename _Car, typename... Cdr >
struct Implementation< _Who, Interface< _Car, Cdr... > >:
virtual public Implementation< _Who, Interface< _Car > >,
virtual public Implementation< _Who, Interface< Cdr... > > {
};
template< typename... Args >
struct Sprite;
// Implementation
template<>
struct Implementation< Sprite< A, B, C >, Interface< A > >:
virtual public Interface< A > {
void a() /* override */ {
std::cout << "Implementation of a() for Sprite< A, B, C >\n";
}
};
template<>
struct Implementation< Sprite< A, B, C >, Interface< B > >:
virtual public Interface< B > {
void b() /* override */ {
std::cout << "Implementation of b() for Sprite< A, B, C >\n";
}
};
template<>
struct Implementation< Sprite< A, B, C >, Interface< C > >:
virtual public Interface< C > {
void c() /* override */ {
std::cout << "Implementation of c() for Sprite< A, B, C >\n";
}
};
template<>
struct Sprite< A, B, C >:
virtual public Implementation< Sprite< A, B, C >, Interface< A, B, C > > {
};
template< typename _Sprite >
struct BaseState {
_Sprite & sprite_;
BaseState(
_Sprite & sprite):
sprite_(sprite) {
}
};
template< typename _Sprite, typename... Args >
struct State;
template<>
template< typename _Sprite, typename _Car, typename... Cdr >
struct State< _Sprite, _Car, Cdr... >:
virtual public BaseState< _Sprite >,
virtual public Implementation< _Sprite, Interface< _Car > >,
public State< _Sprite, Cdr... > {
State(
_Sprite & sprite):
BaseState< _Sprite >(sprite),
Implementation< _Sprite, Interface< _Car > >(),
State< _Sprite, Cdr... >(sprite) {
}
operator Implementation< _Sprite, Interface< _Car > > &() {
return this->sprite_;
}
};
template<>
template< typename _Sprite, typename _Tag >
struct State< _Sprite, _Tag >:
virtual public BaseState< _Sprite >,
virtual public Implementation< _Sprite, Interface< _Tag > > {
State(
_Sprite & sprite):
BaseState< _Sprite >(sprite),
Implementation< _Sprite, Interface< _Tag > >() {
}
operator Implementation< _Sprite, Interface< _Tag > > &() {
return this->sprite_;
}
};
template< typename... Args >
inline State< Sprite< Args... >, Args... >
step(
Sprite< Args... > & sprite) {
return State< Sprite< Args... >, Args... >(sprite);
}
inline State< Sprite< A, B, C >, A, B >
step(
State< Sprite< A, B, C >, A, B, C > state) {
return State< Sprite< A, B, C >, A, B >(state.sprite_);
}
inline State< Sprite< A, B, C >, A, B, C >
step(
State< Sprite< A, B, C >, A, B > state) {
return State< Sprite< A, B, C >, A, B, C >(state.sprite_);
}
int
main() {
Sprite< A, B, C > sprite;
State< Sprite< A, B, C >, A, B, C > state0(sprite);
std::cout << "State 0:\n";
state0.a();
state0.b();
state0.c();
State< Sprite< A, B, C >, A, B > state1(step(state0));
std::cout << "State 1:\n";
state1.a();
state1.b();
// state1.c(); // compile time error
State< Sprite< A, B, C >, A, B, C > state2(step(state1));
std::cout << "State 2:\n";
state2.a();
state2.b();
state2.c();
} |
