From: mark sparshatt <msparshatt@...>
Date: 2005-04-19T16:56:27+09:00
Subject: Re: [EVALUATION] - E03c - The Ruby Object Model (Revised   Documentation)

Ilias Lazaridis wrote:
> Christian Neukirchen wrote:
> 
>> Ilias Lazaridis <ilias@lazaridis.com> writes:
>>
>>> Ilias Lazaridis wrote:
>>>
>>> an example for wrong ruby documentation:
>>>
>>> -
>>>
>>> cmd:> ri Class
>>>
>>>
>>> "Classes, modules, and objects are interrelated. In the diagram that
>>> follows, the arrows represent inheritance, and the parentheses
>>> meta-classes. All metaclasses are instances of the class `Class'."
>>>
>>>                           +------------------+
>>>                           |                  |
>>>             Object---->(Object)              |
>>>              ^  ^        ^  ^                |
>>>              |  |        |  |                |
>>>              |  |  +-----+  +---------+      |
>>>              |  |  |                  |      |
>>>              |  +-----------+         |      |
>>>              |     |        |         |      |
>>>       +------+     |     Module--->(Module)  |
>>>       |            |        ^         ^      |
>>>  OtherClass-->(OtherClass)  |         |      |
>>>                             |         |      |
>>>                           Class---->(Class)  |
>>>                             ^                |
>>>                             |                |
>>>                             +----------------+
>>
>>
>> I do not see what's wrong here, can you explain?
> 
> 
> definitive errors:
> 
> a) not all arrows represent inheritance, just the verticals.
> 
> b) the relation "(Object)"---[inherits from]--->"Class" is false.
> 
> correct: "(Object)"---[inherits-from]------->nil
> 

As other people have pointed out this is wrong since nothing can inherit 
from nil, since it isn't a class.

The mistake you're making is that (Object) doesn't represent an instance 
of Object. It represents Object's metaclass.

Using _why's metaid library

Object.metaclass.superclass #=> Class

So the ruby documentation is correct, (Object) does inherit from Class

> or
> 
> correct: "(Object)"---[is-an-instance-of]--->Class
> 

This is correct. (Object) both inherits from and is an instance of Class.

> -
> 
> and finally:
> 
> the diagramm gives the impression, that "Object" and "(Object)" (etc.) 
> are both classes,

Object and (Object) are both classes.

> which is of course false. There is a "definition" and 
> an "(instance)".

no there is a "class" and a (metaclass)

--
Mark Sparshatt