gistfile1.rb

# app/business/concert/update.rb
# Concert::RescheduleEmail.sent(concert, new_time)

class Concert::RescheduleEmail
  def self.sent(concert, new_time)
    new(concert, new_time).sent
  end
  
  def initialize(concert, new_time)
    @concert, @starts_at = concert, new_time.to_time
  end
  
  def sent
    if concert.starts_at != new_time
      ConcertMailer.reschedule(concert).deliver_now
    end
  end
end