ruby - Methods_added 用于 Singleton 方法，但不是 Class 方法

Question

我真的不明白这个Ruby Monk exercise :

There's an important nuance that's worth understanding when dealing with singleton_method_added and method_added.

The most natural tack the mind takes with these two callbacks is to assume that method_added will observe instance methods and singleton_method_added, class methods. This, however, is not entirely true; Ruby's singleton object backs normal objects and contains object specific changes. For classes, these are class methods. But when adding a method to a single, regular object, adding instance methods to that object alone modifies the singleton object for that object.

Let me show you why by having you solve this exercise.

练习是:

AN_OBJECT = Object.new

def AN_OBJECT.methods_added
  @@methods_added ||= []
end

def AN_OBJECT.singleton_methods_added
  @@singleton_methods_added ||= []
end

我的尝试是这样做的:

def AN_OBJECT.methods_added
  unless AN_OBJECT.is_a?(Class)
    @@methods_added ||= []
  end
end

def AN_OBJECT.singleton_methods_added
  if AN_OBJECT.instance_of?(Object)
    @@singleton_methods_added ||= []
  end
end

但规范仍然失败。

我真的很难理解他们到底想让我做什么。什么是单例对象？据我所知，单例类是一种“元类”，它的存在只是为了给类的某个实例提供行为。

单例对象是一种“元对象”，它的存在仅仅是为了给对象的某个实例赋予行为吗？这让我很困惑。

Answer 1

Eureka !

AN_OBJECT = Object.new

def AN_OBJECT.methods_added
  @@methods_added ||= []
end

def AN_OBJECT.singleton_methods_added
  @@singleton_methods_added ||= []
end

def AN_OBJECT.singleton_method_added(method_name)
  @@singleton_methods_added ||= []
  @@singleton_methods_added << method_name
end

如果您向上滚动查看之前的练习，它应该会给您足够的提示来说明如何处理它。可惜我这么晚才发布这个..