Re: Limited returns

["Egil Høvik" <egilhovik@hotmail.com>]

On Jun 23, 4:21 pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> Let's consider this:
>
>    with Ada.Finalization;
>    procedure Test_Limited_Stuff is
>       type I is limited interface;
>
>       type T is new Ada.Finalization.Limited_Controlled with record
>          A : Integer;
>       end record;
>
>       type S is new T and I with record
>          Self : not null access S'Class := S'Unchecked_Access;
>       end record;
>
>       function Factory return I'Class is
>       begin
>          return X : S;
> -- GNAT: wrong type for return_subtype_indication
>       end Factory;
>    begin
>       null;
>    end Test_Limited_Stuff;
>
> Is it illegal? I am surprised why? S is in I'Class.
>
> OK, if that is indeed illegal, then let's make another try:
>
>       function Factory return I'Class is
>       begin
>          return X : I'Class := S'(T with others => <>);
> -- GNAT: expected an access type with designated type "S'Class" defined ...
> -- found an access type with designated type "I'Class" defined ...
>       end Factory;
>
> ...still illegal, but more interesting. It seems that a Rosen's trick
> member cannot be initialized because the object's type is more general than
> the designated access type. It should not be so. A compiler bug?
>
> --
> Regards,
> Dmitry A. Kazakovhttp://www.dmitry-kazakov.de



If the goal is to make this compile, do this:

      function Factory return I'Class is
         function S_Factory return S is
         begin
            return X : S;
         end S_Factory;
      begin
         return X : I'Class := S_Factory;
      end Factory;


But then it seems that dispatching on methods of I is broken...
(at least I couldn't get it to work with an abstract procedure.
Didn't
dispatch to the overridden procedure implemented by S or give an
error...)