Re: strange ambiguity in the derived class

Hello,

Trying to compile the example at the end of this post, I am getting
next errors:

[packman@localhost test]$ g++ p.cpp
p.cpp: In member function ?void D::foo1()?:
p.cpp:39: error: request for member ?boo? is ambiguous
p.cpp:16: error: candidates are: const int& B::boo() const
p.cpp:6: error: int& A::boo()
p.cpp: In member function ?void D::foo2() const?:
p.cpp:41: error: request for member ?boo? is ambiguous
p.cpp:16: error: candidates are: const int& B::boo() const
p.cpp:6: error: int& A::boo()

Can someone explain why the example doesn't compile?
The signatures of A:boo() and B:boo() methods are different (one is
const, other isn't).

How to change the example, to make it compile?

Thank in advance.

And the example is here:

#include<iostream>
class A
{
   public:
     virtual ~A(){}
     int& boo()
     { return vboo(); }
   private:
     virtual int& vboo() = 0;
};

class B
{
   public:
     virtual ~B(){}
     const int& boo() const
     { return vboo(); }
   private:
     virtual const int& vboo() const = 0;
};

class C : public A, public B
{
   public:
     C():p(5){}
     virtual ~C(){}
   private:
     virtual const int& vboo() const
     { return p; }
     virtual int& vboo()
     { return p; }
     int p;
};

class D
{
   public:
     void foo1()
     { std::cout<<"D::foo1() ++c.boo()="<<++c.boo()<<std::endl; }
     void foo2() const
     { std::cout<<"D::foo1() c.boo()const="<<c.boo()<<std::endl; }
   private:
     C c;
};

int main()
{
   D d;
   d.foo1();
   d.foo2();
}