convert "class of" in pascal to D.

[Paulo Pinto]

Am 30.01.2013 18:18, schrieb dennis luehring:
> Am 30.01.2013 17:16, schrieb Eko Wahyudin:
>> thanks all,
>>
>> I think i am understand, if the closest solution is template,
>> there is no solution in D for my code like this.
>>
>> type
>>         TMyObjectClass = class of TMyObjectA;
>>
>> var
>>         ClassArray : array of TMyObjectClass; //the content
>> initialized
>> randomly
>>         ObjectArray : array of TMyObjectA;
>>         i, j : Integer;
>>
>> procedure CreateAllObject;
>> begin
>>         J:= length(ClassArray);
>>         for I:= 0 to J do begin
>>           ObjectArray[I]:= ClassArray[I].Create({some argument});
>>         end;
>> end;
>>
>> if D unable to do this, I think we must do something with D.
>>
>> I'm still thinking, why constructor in D adopt C++ style rather
>> than pascal style, while pascal style is better :-?
>
> sorry but the pascal "class of"-type and the ctor-derivation isn't that
> super-mighty at all
> as long as the ctors of your object are the same everything is fine
> else -> the feature isn't useable anymore, then you need a real object
> factory
>
> 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.

You can do lots of cool tricks with metaclass programming, specially in 
Smalltalk.


--
Paulo