From: Gavin Sinclair <gsinclair@...>
Date: 2002-12-01T23:58:50+09:00
Subject: class << self  (was Re: [FAQ] What do some of Ruby's symbols mean?)

From: "Shannon Fang" <xrfang@hotmail.com>


> Hi,
> On Sun, 1 Dec 2002 23:35:30 +0900
> ts <decoux@moulon.inra.fr> wrote:
>
>
> >  If instance methods are stored in the class, where do you think that the
> >  class methods are stored ?
>
> I'm sorry I can't understand the purpose of your question. Is it related
> to understanding class << object? The level I'm interested in is for
> application developers, why they need to use <<, does it make their life
> easier, or...? I did not consider to make the language developer's life
> easier.. (sorry for being selfish :-p).
>
> Shannon


You know what a class method is, right?

  class Example
    def Example.foo
      19
    end
  end

  Example.foo           # -> 19


The same is achieved with

  class Example
    class << self
      def example
        19
      end
    end
  end

I don't know why and I don't like it.  I'm happy enough with singleton objects
(but what's wrong with "def obj.meth"?):

  class << object
    def to_s
      "something unexpected"
    end
  end

But I don't see why I should juggle Ruby meta-class models in my head just to
define class methods.

One advantage of the apparently beautiful "class << self" is that you can
define several class methods at once without explicitly typing the class name,
but I don't see what's gained here.  To me it's obfuscated, and even when
understood - or merely acknowledged - I think the notation is unintuitive.

Hopefully I'm missing something and am about to have my fourth Ruby epiphany :)

Gavin