Should this be legal?

["Oliver Kellogg" <oliver.kellogg@vs.dasa.de>]

Hello Ada experts,

The full declaration of the Derived type looks different than
the partial view (Base_2 vs. Base(2))

Should this be legal?
Rational Apex 3.2.0b and GNAT 3.13p both accept it.
(However, both compilers tend to have problems with this
type of construction - especially in more complicated contexts.)

But then, if Base_2 and Base(2) are supposedly interchangeable,
how come the function Legal is accepted but function Illegal is
refused ("constraint not allowed here") ?

Thanks,

Oliver M. Kellogg


-- subtyped_discriminant.ads

package Subtyped_Discriminant is

   type Base (N : Integer) is tagged null record;

   subtype Base_2 is Base (2);

   type Derived is new Base_2 with private;

private

   type Derived is new Base (2) with null record;

   -- However,

   function Legal return Base_2;

   function Illegal return Base (2);

end Subtyped_Discriminant;