#include <iostream>
#include <string>

class is_printable {
public:
    virtual std::ostream& print() const = 0;
};

class A : public is_printable {
public:
    A(std::string s)
        : _s(s)
    {
    }
    std::ostream& print() const override
    {
        return std::cout << _s;
    }

private:
    std::string _s;
};

class B : public is_printable {
public:
    B(int s)
        : _s(s)
    {
    }
    std::ostream& print() const override
    {

        return std::cout << _s;
    }

private:
    int _s;
};

std::ostream& operator<<(std::ostream& s, const is_printable& o)
{
    return o.print();
}

int main()
{
    A a("Tekst");
    B b { 123 };

    std::cout << "a:\t" << a << "; b:\t" << b << "\n";
    is_printable& a_r = a;
    is_printable& b_r = b;

    std::cout << "a_r:\t" << a_r << "; b_r:\t" << b_r << "\n";
}