class Point
    attr_accessor :x, :y

    def initialize( x, y )
        @x = x
        @y = y
    end

    def to_s
        "(#{@x}, #{@y})"
    end
end

# inheritance is signified with the < symbol
class Rectangle < Point
    attr_accessor :width, :height

    def initialize( width, height )
        @width = width
        @height = height
    end

    def to_s
        "#{@width} x #{@height} @ #{super.to_s}"
    end
end

# ruby doesn't have multiple inheritance, but it does have modules and mixins