Declare a method of class template as friend funciton

friend class template method.cpp

// Generic template
template <typename T>
struct Foo {
	static int bar(const T& t) { return -1; }
};

// Specialization
class C;

template<>
class Foo<C> {
public:
	static int bar(const C& c);
};

// Class for template parameter
class C {
public:
	C(int i): i_(i) {}

	friend int Foo<C>::bar(const C&);
private:
	int i_;
};

// Implementation of template specialization
int Foo<C>::bar(const C& c) {
	return c.i_;
}