给定一个Ruby对象的实例,我如何获得它的元类？

Question

通常,我可能会使用以下内容获取Ruby对象的特定实例的元类:

class C
  def metaclass
    class << self; self; end
  end
end

# This is this instance's metaclass.
C.new.metaclass => #<Class:#<C:0x01234567>>

# Successive invocations will have different metaclasses,
# since they're different instances.
C.new.metaclass => #<Class:#<C:0x01233...>>
C.new.metaclass => #<Class:#<C:0x01232...>>
C.new.metaclass => #<Class:#<C:0x01231...>>

假设我只想知道任意类的任意对象实例的元obj类,并且我不想metaclass在类的上定义(或类似)方法obj.

有没有办法做到这一点？

Answer 1

官方名称是singleton_class.获取它的方法(在Ruby 1.9.2中)很简单:

obj.singleton_class

对于较旧的Ruby版本,您可以使用backports:

require 'backports/1.9.2/kernel/singleton_class'
obj.singleton_class
# or without using backports:
class << obj; self; end

Answer 2

是的.

metaclass = class << obj; self; end