From: Ilias Lazaridis <ilias@...>
Date: 2005-04-19T19:39:37+09:00
Subject: Re: [EVALUATION] - E03c - The Ruby Object Model (Revised   Documentation)

mark sparshatt wrote:
> 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.

simply rephrase to:

"Object inherits from nothing" or

"Object does not inherit".

> The mistake you're making is that (Object) doesn't represent an instance 
> of Object. 

I understand.

Thus horizontal arrows represent inheritance, too.

Let's see.

> It represents Object's metaclass.

again my initial question:

how do I access this metaclass?

> Using _why's metaid library

this library is irrelevant.

I'm evaluating standard ruby and its Object Model.

The [Meta] Object Model must be accessible without additional libraries.

> Object.metaclass.superclass #=> Class

output of pure ruby:

irb(main):014:0> Object.metaclass.superclass
NoMethodError: undefined method `metaclass' for Object:Class
         from (irb):14

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

not in my installation:

I have no "(Object)"

>> or
>>
>> correct: "(Object)"---[is-an-instance-of]--->Class
> 
> This is correct. (Object) both inherits from and is an instance of Class.

it's easier:

(Object) is not existent.

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

"Object" and "(Object)" are essentially the same thing.

>> which is of course false. There is a "definition" and an "(instance)".
> 
> no there is a "class" and a (metaclass)

there are no metaclasses in ruby.

If i'm wrong:

please show me the pure-ruby [no additional libraries] access-code.

-

The version 1.1 UML diagramm backups all my statements.

You can verify it with a standard ruby installation:

http://lazaridis.com/case/lang/ruby/

..

-- 
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