[fpc-devel] type classes

[Mattias Gaertner]

On Sun, 21 Oct 2007 14:10:37 +0200
Peter Vreman <peter at freepascal.org> wrote:

> At 14:03 21-10-2007, you wrote:
> >On Sun, 21 Oct 2007 13:46:57 +0200
> >Florian Klaempfl <florian at freepascal.org> wrote:
> >
> > > Mattias Gaertner schrieb:
> > > > Is it possible to use TTranslateStrings = type TStrings?
> > > > I ask because, the compiler allows it, but stops later with only
> > > > this message:
> > > > lcl/interfaces/gtk2/interfaces.pas(1,1) Fatal: Compilation
> > > > aborted
> > > >
> > > > Question:
> > > > Is it allowed to use
> > > > NewClass = type SomeClass;
> > > > ?
> > >
> > > In theory yes, in pratice it seems to be buggy :)
> >
> >Thanks for the quick response.
> 
> Also delphi handles things strange. The following code is from 
> webtbf/tw3930a.pp. The code looks correct, but delphi fails with 
> "Incompatible types: 'TMyStringList' and 'TStringList'". That makes 
> typed classes not very usefull unless you override all constructors.
> 
> 
> uses
>    Classes;
> 
> type
>    TMyStringList = type TStringlist;
> 
> var
>    list : TMyStringList;
> 
> begin
>    list:=TMyStringList.Create;
> end.

It might sound strange, but this 'incompatible types' is good.

I need it only for RTTI. A TMyStringList will never be created. 
Basically I need

type
  TTranslateStringsText = type TStrings;
  
  TMyComponent = class(TPersistent)
    ...
  published
    property Items: TTranslateStringsText read ... write ...;
  end;

The implementation will always use TStrings, not TTranslateStringsText.
Only the RTTI information should show TTranslateStringsText.
Especially this must work: 
  Items:=TStringList.Create;

BTW, I don't know what other sense is in 'type someclass'. Maybe
Borland thought the same.


Mattias