In the below program, there are two structs A and B, each with its own method f and comparison operator ==. And the struct C inherits both A and B together with their methods. Then the program calls method and operator of an object of type C:
struct A {
bool f(const A &) const;
bool operator ==(const A &) const;
};
struct B {
bool f(const B &) const;
bool operator ==(const B &) const;
};
struct C : A, B {};
int main() {
B b;
C c;
//c.f(b); // error everywhere
//c.operator ==(b); //error everywhere
(void)(c == b); //error in GCC, ok in Clang and MSVC
}
The call to method f fails due to ambiguity as explained in the question Why do multiple-inherited functions with same name but different signatures not get treated as overloaded functions? . The same ambiguity error happens with explicit call to operator ==.
But the expression c == b is rejected only by GCC, while both Clang and MSVC accept it. Demo: https://gcc.godbolt.org/z/nhM1MzTM4
Which compiler behavior is right here?
