[fpc-pascal] Class reference doubt

[Luiz Americo Pereira Camara]

On 24/11/2011 05:47, Graeme Geldenhuys wrote:
> On 2011-11-24 03:58, Luiz Americo Pereira Camara wrote:
>> possible to get the expected behavior without forcing programmer to
>> create a virtual constructor by using the new RTTI
> What has the "new RTTI" got to do with anything?
>
> Simply define TObj.Create as virtual, and TFoo.Create as overridden.
> This is rather normal coding practise with classes. Nothing special.

This solution is not quite generic because is necessary to descend from 
an specific class and also needs to change an interface declaration. So 
to use in old code / classes it would be necessary to change the 
hierarchy and the interface.

Also it would not work with classes that i cant change the hierarchy 
like rtl ones or third party

With Delphi is possible to call a constructor even if has a different 
name from Create and with parameters without changing interface or hierarchy

It seems useful for me

Luiz

>
> ----8<-------------8<-------------8<-------------8<-------------8<----
> program test;
> {$mode ObjFpc}{$H+}
> type
>    TObj = class
>    public
>      constructor create; virtual;
>    end;
>    TObjClass=class of TObj;
>
>    TFoo = class(TObj)
>    public
>      constructor create; override;
>    end;
>
> constructor TObj.Create;
> begin
>    inherited create;
>    WriteLn('TObj.create');
> end;
>
> constructor TFoo.create;
> begin
>    inherited Create;
>    WriteLn('TFoo.Create');
> end;
>
> var
>    cls: TObjClass;
>    obj: TObj;
> begin
>    cls := TFoo;
>    WriteLn('cls class is ',cls.ClassName);
>    Obj := cls.Create;
>    Obj.Free;
> end.
> ----8<-------------8<-------------8<-------------8<-------------8<----
>
>
> And here is the output...
>
> $ ./test
> cls class is TFoo
> TObj.create
> TFoo.Create
>
>
>
> Regards,
>    - Graeme -
>