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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Limited returns
Newsgroups: comp.lang.ada
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Organization: cbb software GmbH
Date: Mon, 23 Jun 2008 16:21:07 +0200
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Date: 2008-06-23T16:21:07+02:00
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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. Kazakov
http://www.dmitry-kazakov.de