Inherit several bases by using variadic templates

variadic_inheritance.cpp

#include <iostream>
#include <type_traits>
#include <typeinfo>

template <typename BASE, typename ... BASES>
struct MultiDerived : BASE, MultiDerived<BASES> ...
{
    void EveryAction()
    {
        BASE::Action();
        int dummy[sizeof...(BASES)] = {(BASES::Action(), 0)...};
    }
};

template <typename CLASS, typename BASE>
struct Derived : virtual CLASS, BASE
{
};

template <typename CLASS, typename BASE, typename ... BASES>
struct UniquelyDerived : UniquelyDerived<UniquelyDerived<CLASS, BASE>, UniquelyDerived<CLASS, BASES ...>>
{
};

template <typename CLASS, typename BASE>
struct UniquelyDerived<CLASS, BASE> : /* virtual */ std::conditional<std::is_base_of<BASE, CLASS>::value, CLASS, Derived<CLASS, BASE>>::type
{
    void EveryAction()
    {
    }
};

struct Base1
{
    Base1() { std::cout << "Base1::Base1()" << std::endl; }
    void Action() { std::cout << "Base1::Action()" << std::endl; }
};

struct Base2
{
    Base2() { std::cout << "Base2::Base2()" << std::endl; }
    void Action() { std::cout << "Base2::Action()" << std::endl; }
};

struct Base3
{
    Base3() { std::cout << "Base3::Base3()" << std::endl; }
    void Action() { std::cout << "Base3::Action()" << std::endl; }
};

struct Base4
{
    Base4() { std::cout << "Base4::Base4()" << std::endl; }
    void Action() { std::cout << "Base4::Action()" << std::endl; }
};

struct Base5
{
    Base5() { std::cout << "Base5::Base5()" << std::endl; }
    void Action() { std::cout << "Base5::Action()" << std::endl; }
};

template <typename T>
void print_info()
{
    std::cout << "------------------------------" << std::endl;

    std::cout << "Construction of the object:" << std::endl;
    T object{};

    std::cout << "Use of the object:" << std::endl;
    object.EveryAction();

    std::cout << "Info about the object:" << std::endl;
    std::cout << "- type is " << typeid(T).name() << std::endl;
    std::cout << "- size is " << sizeof(T) << std::endl;

    std::cout << "------------------------------" << std::endl;
}

int main()
{
    print_info<MultiDerived<Base1>>();
    print_info<MultiDerived<Base2, Base4>>();
    print_info<MultiDerived<Base3, Base4, Base5>>();
    //print_info<MultiDerived<Base5, Base5>>();

    std::cout << "------------------------------" << std::endl;

    //print_info<UniquelyDerived<Base1>>();
    print_info<UniquelyDerived<Base1, Base2>>();
    print_info<UniquelyDerived<Base1, Base2, Base2>>();
    print_info<UniquelyDerived<Base1, Base2, Base2, Base2>>();
    print_info<UniquelyDerived<Base1, Base2, Base3, Base4, Base5>>();
    print_info<UniquelyDerived<Base1, Base2, Base3, Base4, Base4, Base4>>();
    print_info<UniquelyDerived<Base1, Base2, Base3, Base4, Base5, Base1>>();
}