gistfile1.rb

class AddComment
  attr_reader :store

  def initializer(store)
    @store = store
    return self
  end

  def call(post_id, comment_attrs)
    post = store.find(post_id)
    comment = post.add_comment(comment_attrs)
    if comment.save
      publish(:success, post, comment)
    else
      publish(:fail, post, comment)
    end
  end
end

class CommentController
  def create
    service = MyApp::AddComment.new(Post)
    service.on(:success) { |post, comment| redirect_to post }
    service.on(:fail)    { |post, comment| @post, @comment = post, comment; render :new }
    service.call(post_id: 1, comment: { body: "cool!"})
  end
end