active support callbacks example

callbacks.rb

class V
  include ActiveSupport::Callbacks  
  define_callbacks :derp
  set_callback :derp, :after, :after_derp
  attr_accessor :x
  def derp
    run_callbacks :derp do
      @x = 1
      puts @x
    end
  end  
  def after_derp
    @x = 2
    puts @x
  end  
end  

[106] pry(main)> z.derp

1

2

=> nil