How do I define friends in global namespace within another C++ namespace?

Question

I\'d like to define a binary operator on in the global namespace. The operator works on a class that is defined in another namespace and the operator should get access to th

Answer 1

First, note that your operator declaration was lacking a namespace qualification for A:

NAME::A operator * (double lhs, const NAME::A& rhs)

and then the decisive trick is to add parentheses to the friend declaration like this, just as you proposed in your "pseudo-code"

friend A (::operator *) (double lhs, const A& rhs);

To make it all compile, you then need some forward declarations, arriving at this:

namespace NAME
{
    class A;
}

NAME::A operator * (double lhs, const NAME::A& rhs);

namespace NAME
{
    class A {
        public:
            friend A (::operator *) (double lhs, const A& rhs);
        private:
            int private_var;
    };
}

NAME::A operator * (double lhs, const NAME::A& rhs)
{
    double x = rhs.private_var;
}

Alexander is right, though -- you should probably declare the operator in the same namespace as its parameters.