convert "class of" in pascal to D.

[Paulo Pinto]

Am 30.01.2013 20:11, schrieb dennis luehring:
> Am 30.01.2013 19:58, schrieb Paulo Pinto:
>> Am 30.01.2013 18:18, schrieb dennis luehring:
>>> in real OOP objects are specialized through its virtual method
>>> implementations AND its ctor-parameters (which are similar in very very
>>> few rare cases)
>>>
>>> for example pseudo code
>>>
>>> class Stream
>>>    virtual read_bytes()...
>>>
>>>    class FileStream: Stream
>>>      this(filename)
>>>
>>>    class NetworkStream: Stream
>>>      this(tcp_ip,timeout)
>>>
>>> Stream[] streams
>>>
>>> streams ~= FileStream("c:/temp/test.txt");
>>> streams ~= NetworkStream("123.112.2.1", 1000);
>>>
>>> stream[n].read_bytes()
>>>
>>> this is a much more common OOP/ctor situation then yours
>>> i think its part of pascal/object delphi to ease the VCL development
>>>
>>> but this can be easily reached with an internal CreateInstance
>>> routine like
>>>
>>> Stream
>>>    virtual Stream CreateInstance()
>>>
>>> and
>>>    FileStream implements CreateInstance() with with return new
>>> FileStream
>>>    NetworkStream "" with new NetworkStream etc.
>>>
>>> so whats the realy big deal/feature of this "class of"-type except for
>>> very trivial OOP case
>>
>> Actually there are many definitions what real OOP means.
>>
>> As for Delphi's case, if I am not mistaken it tries to follow the
>> metaclass concept that Smalltalk has, and Java/.NET have to a certain
>> extent.
>
> no there aren't many definitions but many many missuse of the concept

Well, Smalltalk, Simula, C++/Java/C#, OCaml, CLOS, JavaScript, BETA,
Modula-3, Eiffel, Ada, Sather, and many others. All have different 
concepts what OO should really be.

Enough material to write a few OOPSLA papers I would say.

> you interface is the adaptor, your virtual method code is the special
> behavior, your ctors parameters are the intialisers of the special
> behavior - everything else is just a pseudo-procedural style - its not
> OOP if you need to use casts and ifs on your object-type, thats
> procedural programming with class-based fake-namespaces

There I agree with you. Casts should only be a kind of last resort and 
are mostly a sign of bad design.

>
> can you give me a small example of the metaclass concept of smalltalk -
> related to my simple stream example?
>

Your simple example was correct, as this is not the use case of 
metaclasses. Maybe my post was a bit off topic.

In case you are not familiar with the concept, in Smalltalk everything 
is an object. Every object is of course represented by a class 
description and you create instances of the said classes.

Additionally each class also has a class that represents it. In a simple 
description it allows to manipulate the set of methods, instances and 
other information that represents the real class.

It is also the container for what is known as static methods/variables 
in other languages.

However, given Smalltalk's dynamic behavior, you can on the fly change a 
class's metaclass and with it simulate multiple inheritance, method call 
delegation or other tricks.

If I am not mistaken, Objective-C and Ruby allow similar tricks, given 
their Smalltalk influence.

--
Paulo