inheritance.rb

module Measurable
  def area
    width * height
  end

  attr_reader :width, :height
end

class Rectangle
  include Measurable
 
  def initialize(width, height)
    @width  = width
    @height = height
  end
end

class Square 
  include Measurable

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

p Square.new(4).area