How to take address of an overloaded operator defined as a friend in class body in C++ -

how can take address of overloaded operator defined friend in class body?

i tried following

struct s {   friend bool operator==(s, s) { return true; } };  int main() {   bool (*f)(s, s) = &operator==; } 

but gcc gives error

test.cc: in function ‘int main()’: test.cc:6:30: error: ‘operator==’ not defined    bool (*f)(s, s) = &operator==;                               ^ 

which can fixed declaring operator in (global) namespace:

bool operator==(s, s); 

is there way take address without redeclaring operator?

a name first declared in friend declaration within class or class template x becomes member of innermost enclosing namespace of x, is not accessible lookup (except argument-dependent lookup considers x) unless matching declaration @ namespace scope provided

http://en.cppreference.com/w/cpp/language/friend, emphasis mine.

generally, should declare friends outside of class, unless explicitly want hide them lookup except adl (which might idea , might not, don't have enough experience judge, , depends on situation.).