#include <iostream>

using namespace std;

template <class T> struct A;

class B
{
    template <class T> friend class A;

    int x;

public:

    B(int x) : x(x) {}
};

template <class T> struct A
{
    void func(B b) { cout << b.x << endl; }     
};

int main(void)
{
    A<void> a;

    a.func(B(5));

    return 0;
}

5