C++ - How to introduce overload set from variadic number of bases.

Question

The derived class hides the name of an overload set from the base class if the derived class has the same name defined, but we can always introduce that overload set back wi

Answer 1

Here is a trick how to reduce handwriting:

// U<X,Y> is a binary operation on two classes
template<template<class,class>class U, class... Xs> struct foldr;
template<template<class,class>class U, class X> struct foldr<U,X> : X {};
template<template<class,class>class U, class X, class... Xs> struct foldr<U,X,Xs...> : U<X, foldr<U,Xs...>> {};

// our operation inherits from both classes and declares using the member f of them    
template<class X, class Y> struct using_f : X,Y { using X::f; using Y::f; };

struct A { void f(int) {} };
struct B { void f(char) {} };
struct C { void f(long) {} };

struct D : foldr<using_f, A, B, C> {};


int main() {
    D d;
    d.f(1);
    d.f('1');
    d.f(1L);
    return 0;
}

So we should write foldr once, then write simple ad-hoc operations - using_f, using_g, using_f_g

Maybe there is a way to further simplifying. Let me think a bit...