module Decorator
  def decorate(obj, &block)
    extender = Module.new
    extender.module_eval(&block)
    obj.extend extender
    obj
  end

  module_function :decorate
end

a = []
Decorator.decorate(a) {
  def push(*args)
    puts "They are pushing stuff on us *again*!"
    super
  end
}
a.push 1, 2, 3