Example after refactor

fayes4.rb

class NewRental
  def identifier
    'a latest movie'
  end

  def price(days_rented)
    NewRentalPrice.new(days_rented).amount
  end
end

class ClassicRental
  def identifier
    'an oldie'
  end

  def price(days_rented)
    ClassicalRentalPrice.new(days_rented).amount
  end
end

class DocumentaryRental
  def identifier
    'a documentary'
  end

  def price(days_rented)
    DocumentaryRentalPrice.new(days_rented).amount
  end
end

class CustomerStatement
  attr_reader :price, :days_rented, :rental_type

  def initialize(price, days_rented, rental_type)
    @price       = price
    @days_rented = days_rented
    @rental_type = rental_type
  end

  def movie_identifier
    rental_type.identifier
  end

  def to_s
    "Thanks for renting #{movie_identifier} from Fayes! " \
    "Your total charge is $#{price} for #{days_rented} days."
  end
end

class Rental
  attr_reader :days_rented, :movie_type

  def initialize(days_rented, movie_type)
    @days_rented = days_rented
    @movie_type = movie_type
  end

  def statement
    @statement = CustomerStatement.new(price, days_rented, rental_type)
  end

  def price
    rental_type.price
  end

  private

  def rental_type(movie_type)
    if movie_type == 'documentary'
      DocumentaryRental.new(days_rented)
    elsif movie_type == 'new'
      NewRental.new(days_rented)
    elsif movie_type == 'classic'
      ClassicRental.new(days_rented)
    end
  end
end