From: Robert Klemme <bob.news@...>
Date: 2006-02-02T18:38:20+09:00
Subject: Re: Class vs. Object

James Herdman wrote:
> First of all, thanks to everyone who's replied so far.  I appreciate
> the help and insight.
>
> I think I'm getting the grip of things.
>
>>>> "".kind_of? Object
>> => true
>
> This confused me a bit.  "" is an instance of String, right?  I know
> String is an instance of Object, but that doesn't really make "" an
> Object... or does it?

It does.  Note, that String is an instance of Object (because everything
is an Object in Ruby) as well as being a subclass of Object:

>> String.kind_of? Object
=> true
>> String.ancestors.include? Object
=> true

> Another thing that confused me is this:
>
> String.kind_of? String
> => false

The class object String is by no means an instance of itself.  It's rather
an instance of class Class.

> At first I thought that perhaps an object can't be an instance of
> itself as it, itself, is defining said object (i.e. it is a Class --
> the blueprint). However,
>
> Object.kind_of? Object
> => true

Everything is an Object in Ruby - even the class Object itself.

> and
>
> Module.kind_of? Module
> => true
>
> What am I missing?

(i)
>> Class.superclass
=> Module
>> Class.ancestors
=> [Class, Module, Object, Kernel]

(ii)
>> Module.class
=> Class

Since Module is the super class of Class (i) and Module itself is a class
(ii) obviously Module is an instance of Class as well as Module. :-)

I guess, by now I have completely confused you. :-)  There's a certain
self referentiality in Ruby's class and object model.  But this allows for
some very cool features!

    robert