From: Peter Vandenabeele <peter@...>
Date: 2010-12-06T08:49:26+09:00
Subject: Re: Singleton class, metaclass, eigenclass: what do they mean?

On Sun, Dec 5, 2010 at 11:49 PM, Rick DeNatale <rick.denatale@gmail.com> wrote:
...
>>> The 'things' pointed to by klass pointers are either:
>>
>> Could this be a typo where you intended to say 'super' pointers?
>
> I think I should have said klass or superclass pointers.

If I see correctly, those are really different things. The klass
pointers for all "regular" classes (Class objects) and for virtual
classes (singleton classes (of an object) and metaclasses (of a
class), to follow your terminology) are all uniformily pointing to
the Class object, so not much to see there ... What I was
discussing is the 'super' chain that is relevant for method lookup.

>> $ irb
>> ruby-1.9.2-head > class A < Object; end
>>  => nil
>> ruby-1.9.2-head > A.singleton_class
>>  => #<Class:A>
>> ruby-1.9.2-head > A.singleton_class.superclass
>>  => #<Class:Object>
>> </code>
>>
>
> That's a diference between Ruby 1.9 and 1.8  in 1.8.7
>
> class B < A
> end
>
> B.superclass # => A
> b_sing = class << B; self; end
>
> b_sing.superclass # => #<Class:Class>

Indeed, I saw that too and I am confused by it ...
(that's why I only reported the 1.9.2 case that I understand).

If I understand correctly, also in ruby 1.8.7 the 'super' pointer of
the metaclass of a class, really points to the metaclass of
the superclass of that class (how else could B inherit the
class methods of A ?).

So I do not understand what this means ...
b_sing.superclass # => #<Class:Class>

and even more confusing to me ...
b_sing.superclass.superclass # => #<Class:Class>

It looks like there was a convention to report superclass of all virtual
classes to be #<Class:Class>  (I do not understand that answer).

Thanks for all you time into this ...

Peter