class + object + friend

#include <iostream>
using namespace std;

template <typename ObjectType>
class BaseClass{
public:
    friend ObjectType;

    int Increment(){
        return obj.Increment();
    }
    
    int getStuff() const 
    {
      return stuff;
    }

private:
    static int stuff;
    ObjectType obj;
};

template<typename T>
int BaseClass<T>::stuff = 0;

class ObjectType{
public:     
    int Increment ()
    {
        return BaseClass<ObjectType>::stuff++;
    };
};

int main () {
    BaseClass<ObjectType> base;
    base.Increment(); // should increase stuff by 1;
    cout << base.getStuff() << endl;
    base.Increment(); // should increase stuff by 1;
    cout << base.getStuff() << endl;
}