Replace Conditional with Polymorphism

replace-conditional-with-polymorphism.rb

class MountainBike
  def price
    case @type_code
    when :rigid
      (1 + @commission) * @base_price
    when :front_suspension
      (1 + @commission) * @base_price + @front_suspension_price
    when :full_suspension
      (1 + @commission) * @base_price + @front_suspension_price +
      @rear_suspension_price
    end
  end
end

replacement.rb

module MountainBike
  ...
end

class RigidMountainBike
  include MountainBike
  def price
    (1 + @commission) * @base_price
  end
end

class FrontSuspensionMountainBike
  include MountainBike
  def price
    (1 + @commission) * @base_price + @front_suspension_price
  end
end

class FullSuspensionMountainBike
  include MountainBike
  def price
    (1 + @commission) * @base_price + @front_suspension_price +
    @rear_suspension_price
  end
end