decorator.rb

class Coffee
  def cost
    3.00
  end
end

class SprinkledCoffee
  def initialize(coffee)
    @base_cost  = coffee.cost
  end

  def cost
    @base_cost + 1.50
  end
end

class WhippedCoffee
  def initialize(coffee)
    @base_cost = coffee.cost
  end

  def cost
    @base_cost + 2.00
  end
end


my_coffee = Coffee.new
my_coffee.cost # => 3.00

fancier_coffee = SprinkledCoffee.new(my_coffee)
fancier_coffee.cost # => 4.50

fanciest_coffee = WhippedCreamCoffee.new(SprinkledCoffee.new(my_coffee))
fanciest_coffee.cost # => 6.50