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operator2.cpp

#include <iostream>

using namespace std;

class Base {
 public:
    Base() {}
    virtual ~Base() {};
    virtual ostream &print(ostream &o) const = 0;

 protected:
    int id;
};

class Derived: public Base {
 public:
    Derived() {}
    Derived(int i) {
        Base::id = i, id2 = 123;
    }
    ~Derived(){}
    ostream &print(ostream &o) const {
        o << "id = " << Base::id << "\n";
        o << "id2: " << id2 << "\n";
        return o;
    }
 private:
    int id2;
};

class Derived2: public Base {
 public:
    Derived2() {}
    ~Derived2() {}
    ostream &print(ostream &o) const {
        o << "id = " << Base::id << "\n";
        o << "name = " << name << "\n";
        return o;
    }
 private:
    string name = "Another type from another class to print";
};

ostream &operator<<(ostream &o, Base *d) {
    d->print(o);
    return o;
}

int main() {
    Base *d = new Derived(20);
    Base *d2 = new Derived2();

    cout << d;
    cout << "--\n";
    cout << d2;

    delete d;
    delete d2;

    return 0;
}