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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Bug with variant derived from interface?
Date: Wed, 3 Jun 2009 15:12:56 -0700 (PDT)
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Date: 2009-06-03T15:12:56-07:00
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On Jun 3, 10:09=A0am, "Alex R. Mosteo" <alejan...@mosteo.com> wrote:
> Before reporting a bug to Adacore I'd like to have your opinion. With the
> following test program I get the error below in both GPL2008/2009.
>
> procedure Bugcase is
>
> =A0 =A0-- =A0type Base is abstract tagged null record;
> =A0 =A0-- =A0This works
>
> =A0 =A0type Base is interface;
> =A0 =A0-- =A0This does not work.
>
> =A0 =A0type Derived_Ok (X : Boolean) is new Base with null record;
>
> =A0 =A0type Derived_Also_Ok (X : Boolean) is new Base with record
> =A0 =A0 =A0 Y : Integer;
> =A0 =A0end record;
>
> =A0 =A0type Derived_Bad (X : Boolean) is new Base with record
> =A0 =A0 =A0 -- =A0Above line is the one failing.
> =A0 =A0 =A0 case X is
> =A0 =A0 =A0 =A0 =A0when others =3D> null;
> =A0 =A0 =A0 end case;
> =A0 =A0end record;
>
> begin
> =A0 =A0null;
> end Bugcase;
>
> $ gnatmake bugcase.adb
> gcc -c bugcase.adb
> bugcase.adb:14:09: call to abstract function must be dispatching
> gnatmake: "bugcase.adb" compilation error

I don't see any reason this program should be illegal.  The message
involving a "call to abstract function" is certainly wrong, because
there aren't any abstract function calls involved.  (Just as a wild
guess, I'm guessing that the abstract function GNAT is complaining
about is "=3D", and there's some special subroutine that tries to
compose the equality function for variant records that isn't handling
this case right...  did I come close???)

                               -- Adam