[fpc-devel] RFC: Delphi style class helpers

[Paul Ishenin]

21.12.2010 3:37, Sven Barth wrote:

> Especially at the core devs, but maybe also for other interested persons
> I have the following questions regarding the implementation of this
> feature:
> - should class helpers have access to protected fields of the extended
> class? I propose not or this would beat the complete idea of "sealed" (I
> also believe that Delphi doesn't allow it as well)

Protected, strict protected and private but not strict private.

> - should class helpers be able to be instantiated or even referenced in
> any way? (including forward declarations)

no

> - should class helpers be allowed to override/reintroduce methods?

reintroduce - yes, but since class helper is not a child class using 
reitroduce does not do anything.

> - should class helpers be able to extend other class helpers (as class
> helpers are implemented as child classes of the extended class this
> might currently be possible)?

no

> - should class helpers be able to implement interfaces?

This needs to be tested but I don't think they can. You can't define a 
helper that implements interface - so all interfaces should be listed in 
class. Another thing that you can reintroduce QueryInterface, 
GetInterface in the helper but I don't think they will be used by 'is' 
and 'as' operators.

> - can/should "message" methods be forbidden?

In delphi they are not forbidden but also they can't be reached by 
Dispatch call.

> - should abstract methods be forbidden?

In delphi they are not forbidden and require an implementation. It looks 
tht delphi skips 'abstract'. Also delphi skips 'virtual' and 'dynamic'. 
I think in FPC this should be forbidden.

> - should a class helper for class X hide a method which was introduced
> in a subclass of X?

no

> - can class helpers extend generic classes?

no one example I tried was able to compile

I have attached few tests which answers to most of your questions.

Best regards,
Paul Ishenin
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