#ifndef POLYGON_HPP
#define POLYGON_HPP

class polygon
{
	protected:
		double side_length_;

	public:
		polygon() : side_length_(0)
		{}

		void set_side_length(double side_length)
		{
			side_length_ = side_length;
		}

		virtual double area() const = 0;
};

// the types of the class factories
typedef polygon* create_t();
typedef void destroy_t(polygon*);

#endif