From: Rick DeNatale <rick.denatale@...>
Date: 2009-12-11T22:49:39+09:00
Subject: Re: solve this ruby problem

On Fri, Dec 11, 2009 at 6:38 AM, Howard Roberts
<howardroberts@comcast.net> wrote:
>  I can tell you this:
>
> (pretty much) Everything in Ruby is a class

No my friend, most things in Ruby are not classes, (pretty much)
everything in Ruby is an object, and objects have classes, some
objects have singleton classes, which give them extra methods or
override methods they would have otherwise gotten from their class and
its parents (superclasses). Classes, themselves, being objects have a
class called Class, and all have a singleton class which gives them
additional methods (class methods) which are in addition to or
override methods provided by Class.

There's at least one subtle difference, relating to the meaning of
singleton, between singleton classes of ordinary objects and singleton
classes of classes. Methods defined in the singleton class of an
ordinary object only apply to that individual object instance, whereas
methods defined in the singleton class of a class are available to
that class and any of its subclasses.  The difference is that in the
first case the superclass field of the singleton class refers to the
object's class, while in the latter it refers to the singleton class
of the class's superclass.  So while some consider class methods to be
'singleton methods' of the class, a case can be made that this isn't
really true, particularly if the class has any subclasses, because the
class methods apply to more than a single object.

-- 
Rick DeNatale

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