Variation of RubyTapas episode "021 Domain Model Events" without using callbacks

tasks_controller_refactoring.rb

class TasksController < ApplicationController
  def update
    if @task.update_attributes(params[:task])
      tracker = PostSaveTaskTracker.new(@task)
      TaskPusher.new(tracker, socket_id).push_changes
      TaskMailSender.new(tracker, current_user).deliver_email
      # success response
    else
      # failure respond
    end
  end
end

class TaskTracker < Struct.new(:task)
  def changed?(attribute)
    if changes.has_key?(attribute)
      prev_attr, curr_attr = changes[attribute]
      prev_attr != curr_attr
    end
  end
  
  def changes
    task.changed_attributes
  end
end

class PostSaveTaskTracker < TaskTracker
  def changes
    task.previous_changes
  end
end

class TaskPusher < Struct.new(:tracker, :socket_id)
  def push_changes
    if tracker.changed?("assignee")
      # push assignee changes
    end
    if tracker.changed?("project_id")
      # push project changes
    end
  end
end

class TaskMailSender < Struct.new(:tracker, :recipient)
  def deliver_email
    if tracker.changed?("status")
      # email status change
    end
    if tracker.changed?("assignee")
      # email assignee change
    end
  end
end