From: "David A. Black" <dblack@...>
Date: 2005-11-24T11:51:58+09:00
Subject: Re: A question about metaclass

Hi --

On Thu, 24 Nov 2005, Daniel Sheppard wrote:

>> My question is where the C.new method is.
>> The class Class or C's singleton class?
>>
>> According to PickAxe2, it seems that C.new is in Class.
>> However, according to Little Ruby book, it seems that C.new
>> is in C's metaclass.
>
> class C
> end
>
> C.new #executed new from Class
>
> class C
>  def new(arg)

You're defining C#new (an instance method of C).  Do you mean to
define:

   def C.new(arg)

?

>    p "ARGGGHHH!! #{arg}"
>    super.new

If you are defining C.new, then super will return an instance of C:

   class C
     def C.new
       super
     end
   end

   C.new    # #<C:0x355e9c>

If you call new on that object, you'll get an NoMethodError :-)

>  end
> end

See if this helps:

   class C
   end

   p C.new

   def C.new
     puts "Here"
     super
   end

   p C.new

> C.new #executed new from C's metaclass/singleton class/eigenclass.

(class << obj; self; end) is obj's singleton class.  Sometimes the
singleton class of a class object is also called a "metaclass" (though
there's been debate as to whether a separate term is needed, and
whether "metaclass" is the best separate term).  "Eigenclass" is just
one of maybe 25 words that have been suggested for a future "official"
term, since Matz has said he's thinking about what the best term might
be.


David

-- 
David A. Black
dblack@wobblini.net