dip_example_2.rb

class EmailList
  attr_reader :mailer
  delegate :send_email, :to => :mailer
  def initialize(mailer_type)
    @mailer = mailer_type.new
  end
end
# in RottenPotatoes EmailListController:
def advertise_discount_for_movie
  moviegoers = Moviegoer.interested_in params[:movie_id]
  mailer = if Config.has_amiko? then Amiko else MailerMonkey end
  EmailList.new(mailer).send_email_to moviegoers
end