After Inherited callback

after_inherited.rb

module App::AfterInherited
  # Ruby 2.1	
  # http://stackoverflow.com/questions/7093992/how-to-have-an-inherited-callback-in-ruby-that-is-triggered-after-the-child-clas?answertab=active#tab-top
  # http://t-a-w.blogspot.com/2007/04/settracefunc-smoke-and-mirrors.html
  # end - module/class definition ended


  # usage:
  #
  # class A
  #   extend App::AfterInherited
  #
  #   def self.inherited(child)
  #     after_inherited do
  #       puts "XXX - after YYY"
  #     end
  #   end
  # end
  #
  # class B < A
  #   puts "YYY"
  #   # .... code here can include class << self, etc.
  # end
  #
  # Output:
  # => YYY
  # => XXX - after YYY
  #
  def after_inherited(child = nil, &block)
    line_class = nil
    set_trace_func -> (event, file, line, id, binding, classname) do
      unless line_class
        # save the line of the inherited class entry
        line_class = line if event == 'class'
      else
        # check the end of inherited class
        if line >= line_class && event == 'end'
          # if so, turn off the trace and call the block
          set_trace_func nil
          block.call(child)
        end
      end
    end
  end

end