在Ruby中覆盖方法调用？

# the current implementation of Test,defined by someone else
# and for that reason we might not be able to change it directly
class Test
  def self.items
    @items ||= []
  end
end

# we open the class again,probably in a completely different
# file from the definition above
class Test
  # open up the metaclass,methods defined within this block become
  # class methods,just as if we had defined them with "def self.my_method"
  class << self
    # alias the old method as "old_items"
    alias_method :old_items,:items
    # redeclare the method -- this replaces the old items method,# but that's ok since it is still available under it's alias "old_items"
    def items
      # do whatever you want
      puts "items was called!"
      # then call the old implementation (make sure to call it last if you rely
      # on its return value)
      old_items
    end
  end
end

我使用类<<重写了你的代码.自我语法打开元类,因为我不知道如何在类方法上使用alias_method.