polymorp.rb

def link_to_notifiable(notifiable)
  notifiable.link_to_notifiable(self)
end

# concerns/notifiable_presenters.rb
class Answer
  def link_to_notifiable(helper)
    helper.link_to_answer, question
  end
end

class Comment
  def link_to_notifiable(helper)
    helper.link_to_comment, to_question
  end
end

class Favorite
  def link_to_notifiable(helper)
    helper.link_to_question, question
  end
end

class Question
  def link_to_notifiable(helper)
    helper.link_to_question, self
  end
end