Can't overload i/o operators for private enum in namespace

Question

I have a private enum in a class within a namespace. I'm trying to overload the I/O operators, but all I get is the compiler complaining about the Enum being private. The solution from this post did nothing to help me. Here is an isolated version of my problem.

TestClass.h

#include <iostream>
namespace Test
{
    class TestClass
    {
        enum Enum : unsigned int {a = 0, b};
        friend std::ostream& operator<<(std::ostream& os, Enum e);
    };
    std::ostream& operator<<(std::ostream& os, TestClass::Enum e);
};

TestClass.cpp

#include "TestClass.h"
std::ostream& operator<<(std::ostream& os, Test::TestClass::Enum e)
{
    //do it
}

The compiler complains about this, but does not complain when I remove the class from the namespace, so how do I get this to compile?

I'm using

g++ -c TestClass.h

to compile this

Answer 1

The operator in your cpp file is not the friend you declared. The friend is a member of the namespace, because the class it's declared in is a member.

So wrap the operator definition in the namespace scope too. Or fully qualify the defintion

std::ostream& Test::operator<<(std::ostream& os, Test::TestClass::Enum e)
{
    //do it
}