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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: GNAT GPL 2013 bug?
Date: Fri, 9 Aug 2013 13:36:00 +0200
Organization: cbb software GmbH
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Date: 2013-08-09T13:36:00+02:00
List-Id: <comp.lang.ada>

On Fri, 9 Aug 2013 04:06:32 -0700 (PDT), sbelmont700@gmail.com wrote:

> In 3.10~13.1/2:
> 
> "In addition, the anonymous access subtype defined by the
> access_definition for a controlling access parameter (see 3.9.2) excludes
> null."
> 
> So apparently yes, adding 'tagged' to Q should make it toss an exception.

package P is
   type Q is private;
   procedure P (X : access Q) is null;
   ...
end P;

How does a client know if null is a valid value here? It could be

private
   type Q is tagged null record;

or

private
   type Q is null record;

Let I pass it to a generic:

generic
   type T is private;
   with procedure P (X : access T) is <>;
package Foo is

How Foo is supposed to know if P should raise with null?

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de