In-Class stuff

notes/4_19/decorator.cpp

+#include <iostream>
+
+using namespace std;
+
+class shape {
+public:
+	virtual ~shape() {}
+	virtual void draw() = 0;
+};
+
+class square : public shape {
+public:
+	void draw()
+	{
+		cout << "[]" << endl;
+	}
+};
+
+class circle : public shape {
+public:
+	void draw()
+	{
+		cout << "()" << endl;
+	}
+};
+
+// What if we want to add colors?
+
+// We could extend square for every color,
+// or attribute, but that doesn't scale well
+class green_square : public square {
+public:
+	void draw()
+	{
+		cout << "green-[]" << endl;
+	}
+};
+
+// Better way: Decorator pattern
+class shape_decorator : public shape {
+private:
+	shape *s;
+public:
+	shape_decorator(shape *s) : s(s) {}
+	~shape_decorator() { delete s; }
+	void draw() { s->draw(); }
+};
+
+class green_shape : public shape_decorator {
+public:
+	green_shape(shape *s) : shape_decorator(s) {}
+	void draw() {
+		cout << "green-";
+		shape_decorator::draw();
+	}
+};
+class big_shape : public shape_decorator {
+public:
+	big_shape(shape *s) : shape_decorator(s) {}
+	void draw() {
+		cout << "BIG-";
+		shape_decorator::draw();
+	}
+};
+
+class cute_shape : public shape_decorator {
+public:
+	cute_shape(shape *s) : shape_decorator(s) {}
+	void draw() {
+		cout << "cute-";
+		shape_decorator::draw();
+	}
+};
+
+int main(int argc, char *argv[]) {
+	square s;
+	circle c;
+	green_square gs;
+
+	s.draw();
+	c.draw();
+	gs.draw();
+
+	green_shape d(new square);
+	d.draw();
+
+	big_shape bs(new big_shape(new circle));
+	bs.draw();
+	return 0;
+}