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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT GPL 2013 bug?
Date: Mon, 12 Aug 2013 15:12:51 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2013-08-12T15:12:51-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:k71biho5pjg7.16zreugtnwyc6$.dlg@40tude.net...
> On Fri, 09 Aug 2013 16:04:02 -0400, Robert A Duff wrote:
...
> BTW, why Ada 2005 used incompatible null-exclusion instead of compatible
> null-permission, e.g.
>
>   procedure P (X : null or access T); -- I accept null
>
> or something like that?

Because that would make the syntax for named access and anonymous access 
different, or would simply move the incompatibility to named access types.

The difference between the default behavior for anonymous and named access 
in Ada 95 was unjustifiable once we had null exclusions. That meant we had 
to break something, and the least painful was the implicit "not null" on 
controlling access parameters (something best avoided anyway, IMHO).

                                  Randy.