gistfile1.hpp

#include <iostream>

using namespace std;

class A {

    public:

        A(int val) : m_val(val) {}

        A& operator=(A& a) {
           m_val += a.m_val;
           return *this;
        }

        int val() { return m_val; }

    protected:

        int m_val;

};

class B : public A {

    public:

        B(int val) : A(val) {}

        B& operator=(B& b) {
            A::operator=(b);
            m_val += 5;
            return *this;
        }

};

int main(int argc, char** argv) {

    A a1(1);
    A a2(2);

    a1 = a2;

    cout << "should be 3: ";
    cout << a1.val() << endl;

    B b1(1);
    B b2(2);

    b1 = b2;

    cout << "should be 8: ";
    cout << b1.val() << endl;

}