From: "Hal E. Fulton" <hal9000@...>
Date: 2002-12-02T11:30:13+09:00
Subject: Re: class << self  (was Re: [FAQ] What do some of Ruby's symbols mean?)

----- Original Message -----
From: "Gavin Sinclair" <gsinclair@soyabean.com.au>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Sunday, December 01, 2002 7:44 PM
Subject: Re: class << self (was Re: [FAQ] What do some of Ruby's symbols
mean?)


> > There's no arcane magic going on here - self is an object of class
> > Class, and in this case it has the value Array.
>
> That, to me, is obfuscated.  'self' is generally understood as the current
> instance of the class.  Therefore, it is only meaningful inside instance
> methods.  In the "class << self" idiom, there is no instance method.
'self'
> may be defined, but it's not *meaningful* in the sense described above.
> There's a yawning gulf between syntax and semantics, and I suggest that
it's
> taking advantage of an undocumented feature.

Hmmmmm. This always makes my brain itch, but I'll make
a stab at it.

I guess I would say that Ruby is OO "even when it isn't" --
in the sense that a "toplevel" method or constant belongs
to Object.

You may argue that it doesn't make sense -- and maybe you
are right -- but I think "self" is always defined in Ruby.
The one-line programs "puts self" and "puts self.class"
will print "main" and "Object" respectively.

Given this paradigm, it does arguably seem natural that in
the middle of a class definition, "self" takes on the value
of the class.

And of course, Class#meth (instance method of Class) means
that there will be a Foo.meth (class method of Foo) for
every class Foo; and a singleton method for the singleton
class of a class is the same as a class method for the
class. Isn't it?  ;)

Hal