aop.rb

module AOP
  def before_advice target_method, &advice
    original_method = :"#original_{sym}"
    self.class.class_eval do
      alias_method original_method, target_method
      define_method target_method do
        advice.call self
        __send__ original_method
      end
    end
  end
end

array = [2, 3, 1]
array.extend AOP

array.before_advice :sort do |obj|
  p "before sort: #{obj.inspect}"
end
array.sort