From: Arlen Cuss <celtic@...>
Date: 2008-02-29T08:48:50+09:00
Subject: Re: constants defined in Kernel are also defined in Object?

On Fri, Feb 29, 2008 at 10:30 AM, Joel VanderWerf
<vjoel@path.berkeley.edu> wrote:
>  But:
>
>
>  Kernel.const_set(:FOO, 42)
>  class Foo; end
>  p Foo::FOO                    # ==> 42
>
> p Foo.const_defined?(:FOO)    # ==> false
>
> p Object.const_defined?(:FOO) # ==> true

Indeed! It works in both cases because Foo is an Object, Object
includes Kernel -- Foo won't tell you that FOO is defined because Foo
didn't define it itself!

I've been writing a new parser and byte-code VM for Ruby recently
(http://rubyex.sairyx.org/, excuse the advertising), which meant
figuring out the whole Ruby object model. This had me tricked at
several stages, but here's how I summarised it to myself:

1. Foo is an instance of Object [eventually].
2. Object mixes in Kernel.
2.a. Kernel's constants are Object's too.
3. Foo::SOME_CONST will see through to Object::SOME_CONST and then
that to Kernel::SOME_CONST.

Correct me if I'm wrong in some detail.

Arlen