From: "Florian Groß" <florgro@...>
Date: 2005-04-20T00:29:34+09:00
Subject: Re: - E03c - The Ruby Object Model (Revised Documentation)

Ilias Lazaridis wrote:

> see my reply to Mr. Matsumoto:
> 
> "class Object inherits from nothing (represented by object nil)"
> 
> new diagramm:
> 
> http://lazaridis.com/case/lang/ruby/

Why is it so hard to say "doesn't inherit" instead of "inherits from 
non-existent"? Expertise isn't making things looking more complex than 
they are -- it is making them as simple as possible, but not any 
simpler. Just remove clutter that doesn't matter and you will end up 
with a diagram that is more clear and easier to understand.

I'm not sure what you mean by the term 'singleton instance' -- classes 
are instances of Class. Whenever you see something like 'foobars' you 
can transform that to 'instances of Foobar' mentally.

What Ruby's singleton classes do is providing a way of treating a single 
Object as if it had a class by itself that nobody else uses. Here is an 
example:

   obj = "hello world"
   def obj.reverse() "fake reverse" end
   obj.reverse # => "fake reverse"
   "foobar".reverse # => "raboof"

Which is equivalent to this:

   obj = "hello world"
   class << obj # enter singleton class
     def reverse() "fake reverse" end
   end # exit singleton class
   obj.reverse # => "fake reverse"
   "foobar".reverse # => "raboof"

And as you can see from this example singleton classes are indeed 
handled as regular classes:

   obj = "hello world"
   class << obj
     # outputs #<Class:#<String:0x2b83cc8>> (or similar)
     p self
     # outputs Class
     p self.class
     # outputs [String, Enumerable, Comparable, Object, Kernel]
     p self.ancestors
     attr_accessor :foo
   end
   obj.methods(false) # => ["foo", "foo="]

That is basically all you need to know about singleton classes. The rest 
is implementation details.

If you really want to give Ruby a look and aren't just doing these 
evaluations to waste your time / boost your curriculum vitae then that 
information will help you. If not then you are probably happy about me 
wasting my time by responding to you. I'm still not sure what your 
intentions are, but I'd certainly like to believe that you are a honest 
person, even though you had a bit of trouble with approaching various 
communities before.

It is okay to ask questions about this relatively exotic parts of Ruby, 
but please do research before asking -- that can mean reading a book 
that is available online for free, buying a book and reading it in 
commute time or just trying things out in IRB / a personal set of unit 
tests.