#include <iostream>

using namespace std;

class Foo {
    private:
        int a = 0;

    public:
        void doA() {
            a += 1;
            cout << "a=" << a << endl;
        }

        virtual void doB() = 0;

};

class Bar: private Foo {
    public:
    static Foo *createFoo() {
        return new Bar();
    }

    void doB() {
        doA();
    }

};

int main()
{
    Foo *f = Bar::createFoo();
    f->doA();
    f->doB();
    delete f;

    return 0;
}