Inheritance Example: Stringable

// stringable.cpp

#include "cmpt_error.h"
#include <iostream>
#include <string>

using namespace std;

// Stringable is an abstract base class (ABC)
class Stringable {
public:
        virtual string to_str() const = 0;
        virtual ~Stringable() { }
};

class Window : public Stringable {
private:
        string name;
        int w; // width
        int h; // height
public:
        Window(const string& init_name, int init_w, int init_h)
        : name(init_name), w(init_w), h(init_h)
        {}

        string to_str() const {
                return "Window(" + name + ", "
                                 + to_string(w) + ", "
                                 + to_string(h) + ")";
        }
}; // Window

// RGB color
class Color : public Stringable {
private:
        int r = 0;   // red, 0 to 255
        int g = 0;   // green, 0 to 255
        int b = 0;   // blue, 0 to 255
public:
        Color() { }  // default constructor

        Color(int init_r, int init_g, int init_b)
        : r(init_r), g(init_g), b(init_b)
        {
                if (r < 0 || r > 255) cmpt::error("red out of range");
                if (g < 0 || g > 255) cmpt::error("green out of range");
                if (b < 0 || b > 255) cmpt::error("blue out of range");
        }

        Color(const Color& other)  // copy constructor
        : Color(other.r, other.g, other.b)
        { }

        int red() const { return r; }
        int green() const { return g; }
        int blue() const { return b; }

        string to_str() const {
                return "rgb(" + to_string(r) + ", "
                              + to_string(g) + ", "
                              + to_string(b) + ")";
        }
}; // Color

struct Point : public Stringable {
        double x = 0.0;
        double y = 0.0;

        Point() { }

        Point(double a, double b)
        : x(a), y(b)
        { }

        string to_str() const {
                return "(" + to_string(x) + ", "
                           + to_string(y) + ")";
        }

}; // Point

ostream& operator<<(ostream& out, const Stringable& s) {
        out << s.to_str();
        return out;
}

int main() {
        Window w("Test", 100, 150);
        cout << w << "\n";

        Color c(100, 100, 120);
        cout << c << "\n";

        Point p{5, -2};
        cout << p << "\n";

        Point origin;
        cout << origin << "\n";
}