Just found that the below works.

Note, that the result type of "a" (overridden) is different. Well, TFoo2 will always satisfy the needs of TFoo, so it seems save. I still found it surprising. Is it intended?

program Project1;
type
   TFoo= class
   public
     function a: TFoo; virtual;
   end;
   TFoo2= class(TFoo)
   public
     function a: TFoo2; override;
   end;
function TFoo2.a: TFoo2;
begin
end;
function TFoo.a: TFoo;
begin
end;
begin
end.

I hope so :) [1]
But it seems (from a 2011 blog) Delphi still doesn't allow that? I wouldn't mind fpc allowed contravariant arguments too ;) (But I guess I only ever missed it once or twice...)

Regards,
Flávio

[1] http://en.wikipedia.org/wiki/Covariance_and_contravariance_%28computer_science%29

Another question that never got answered. Yet I would expect, that either it is implemented with intend, then someone must know. Or it is a bug then that should be checked?

If no one knows, shall I assume it is a bug, and report it?