Method like a class attribute

realistic_way.rb

module ActionView
  module Layouts
    def self.included(base)
      base.extend(ClassMethods)
    end

    module ClassMethods
      def layout
        p 'Hello World'
      end
    end
  end
end


module ActionController
  class Base
    include ActionView::Layouts
  end
end

class ApplicationController < ActionController::Base
  layout

  def say_hello
    p 'Hola'
  end

  def self.say_goodbye
    p 'Chau'
  end
end

a = ApplicationController.new
a.say_hello
ApplicationController.say_goodbye