Ambiguity in a fully qualified static member variable

Question

In this sample code, there is two sentences showing the same static variable. The first one gives no ambiguity, but the second one does, why?

#include <iostream>

using namespace std;

struct A { static const char a = 'a'; };
struct B : public A { };
struct C : public A { };
struct G : public B, public C { };

int main()
{
    G v;

    cout << G::B::A::a << endl;
    cout << v.B::A::a << endl;
}

GCC error (according to some comments, there's no ambiguity in clang):

main.cpp:15:18: error: 'A' is an ambiguous base of 'G'
  cout << v.B::A::a << endl;

Code on coliru

Answer 1

This is clearly a bug in GCC, as a GCC maintainer recommends you report it. However, until it's fixed, you can use a nasty workaround like this:

std::cout << static_cast<B &>(v).A::a;

The advantage is this will help disambiguate if in a (complex) scenario that there are variables with the same name in one of the base classes.