为什么Class是Class的实例，而不是Object的实例? [英] Why is Class an instance of Class, and not of Object?

问题描述

Class.instance_of?(Object)返回 false ，而 Class.instance_of?(Class)返回 true .我觉得这很奇怪，因为我认为 Class 作为一个对象，必须是 Object 类的一个实例.怎么可以成为自己的实例?

Class.instance_of?(Object) returns false, while Class.instance_of?(Class) returns true. I find this surprising because I thought Class, being an object, had to be an instance of the Object class. How can it be an instance of itself?

但是，假设 Class 是 Object 类的一个实例，似乎会导致更令人困惑的问题.由于 Object 是一个类，因此它必须是 Class 类的实例.这是怎么回事?

But assuming that Class is an instance of the Object class seems to lead to an even more confusing issue; since Object is a class, it has to be an instance of the Class class. What is going on here?

推荐答案

Ruby中的类是一流的对象:每个都是类 Class

Classes in Ruby are first-class objects: each is an instance of class Class

因此，您定义的每个类都为您提供:

So every class you define gives you:

  > MyClass.instance_of?(Class)
  => true

在此页面上查看带有继承的图: http://ruby-doc.org/core-2.2.3/Class.html

Check out the diagram with the inheritance on this page: http://ruby-doc.org/core-2.2.3/Class.html

类，模块和对象是相互关联的.在下面的图中，垂直箭头表示继承，而圆括号是元类.所有元类都是类'Class'的实例.

Classes, modules, and objects are interrelated. In the diagram that follows, the vertical arrows represent inheritance, and the parentheses metaclasses. All metaclasses are instances of the class `Class'.

                         +---------+             +-...
                         |         |             |
         BasicObject-----|-->(BasicObject)-------|-...
             ^           |         ^             |
             |           |         |             |
          Object---------|----->(Object)---------|-...
             ^           |         ^             |
             |           |         |             |
             +-------+   |         +--------+    |
             |       |   |         |        |    |
             |    Module-|---------|--->(Module)-|-...
             |       ^   |         |        ^    |
             |       |   |         |        |    |
             |     Class-|---------|---->(Class)-|-...
             |       ^   |         |        ^    |
             |       +---+         |        +----+
             |                     |
obj--->OtherClass---------->(OtherClass)-----------...

这意味着:

  > Class.ancestors 
  => [Class, Module, Object, Kernel, BasicObject]

  > Class.superclass
  => Module
  > Module.superclass
  => Object
  > Object.superclass
  => BasicObject
  > BasicObject.superclass
  => nil

为了对此有更深入的了解，我强烈推荐戴夫·托马斯(Dave Thomas)的电视广播系列: Ruby对象模型和元编程

To get a deeper understanding of this, I highly recommend Dave Thomas's screencast series: The Ruby Object Model and Metaprogramming

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