ruby - 返回当前类的实例

Question

I noticed if I make a subclass which inherits from Datetime , it's .now will return the subclass instance, not Datetime instance.

class MyDateTime < DateTime
end

MyDateTime.now
>#<MyDateTime: 2012-06-05T16:42:57+08:00 ((2456084j,31377s,900801494n),+28800s,2299161j)>

It seems magical. I can't reproduce this behavior in my own class:

class A
  def self.a
   return A.new
  end
end

class B < A
end

B.a
#<A:0x00000001e22358>

I tried to read the source code of DateTime but it's written in C. Is it possible to write a class method which returns an instance of the class it belongs to?

Answer 1

Try it with self:

class A
  def self.a
   return self.new
  end
end

class B < A
end

B.a