Question

This compiles with out problems in VS 2009? Am I stupid?
GCC gives a warning, that the template is private….?
What am I missing?

#include <iostream>

using namespace std;

class A
{
private:
    template<typename T>
    A& operator<<(const T & v)
    {
        cout << v << endl;
        return *this;
    }
};

int main()
{
   A a;
   a << 4;
   system("pause");
}

Answer 1

This code should not compile – this is a bug (or silly extension) in VS. GCC should refuse it as well. The operator is inaccessible in the scope it is used.

Comeau treats this correctly:

"ComeauTest.c", line 28: error: function "A::operator<<(const T &) [with T=int]"
          (declared at line 14) is inaccessible
     a << 4;

EDIT: A relevant standard snippet, from 13.3/1

[Note: the function selected by
overload resolution is not guaranteed
to be appropriate for the context.
Other restrictions, such as the
accessibility of the function, can
make its use in the calling context
ill-formed. ]