add iterable

main.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include "iterators.h"
+
+class IShape {
+	IShape* next = nullptr;
+	IShape* prev = nullptr;
+
+public:
+	virtual ~IShape() = default;
+	virtual void draw() const = 0;
+	virtual double area() const = 0;
+
+	void set_next(IShape* n) {
+		next = n;
+		if (n) n->prev = this;
+	}
+
+	IShape* get_next() const { return next; }
+	IShape* get_prev() const { return prev; }
+
+	template<typename Policy>
+	Traversal<IShape, Policy> traverse() {
+		return Traversal<IShape, Policy>(this);
+	}
+
+	using forward = IteratorForward<IShape>;
+	using backward = IteratorBackward<IShape>;
+};
+
+class Circle : public IShape {
+	double r;
+public:
+	Circle(double radius) : r(radius) {}
+
+	void draw() const override {
+		std::cout << "Drawing Circle of radius " << r << "\n";
+	}
+
+	double area() const override {
+		return 3.14159 * r * r;
+	}
+};