涼風青葉.cpp

#include <iostream>
class ComponentBase {
protected:
    static inline std::size_t component_type_count = 0;
};

template<typename T>
class Component : public ComponentBase {
public:
    static inline std::size_t id = component_type_count++;

    static std::size_t component_type_id() { return id; }
};

class A : public Component<A> {
};
class B : public Component<B> {
};
class C : public Component<C> {
};

int main() {
    std::cout << A::component_type_id() << std::endl;
    std::cout << B::component_type_id() << std::endl;
    std::cout << B::component_type_id() << std::endl;
    std::cout << A::component_type_id() << std::endl;
    std::cout << A::component_type_id() << std::endl;
    std::cout << C::component_type_id() << std::endl;
}