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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT GPL 2013 bug?
Date: Fri, 09 Aug 2013 16:04:02 -0400
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Date: 2013-08-09T16:04:02-04:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> Why? null considered an object is not class-wide, so I see no difference to
> plain parameters. null.Foo would be illegal anyway and Foo (null) would be
> ambiguous (in presence of several overriding instances).

    type T is tagged ...;
    type A is access T'Class;
    procedure P (X: access T);

    X : A := null;
    P(X); -- This is a dispatching call, so it needs to look at
          -- X.all'Tag, which doesn't exist.

- Bob