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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: not null access procedure (was: Re: Dynamic String)
Date: 01 Nov 2005 20:07:47 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2005-11-01T20:07:47-05:00
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Anonymous Coward <bogus_addy@bogus_domain.net> writes:

> In article <1130875772.717413.45520@g14g2000cwa.googlegroups.com>, Matthew Heaney wrote:
> > 
> > Ada 2005 will indeed include a standard container library.  You can
> > find the latest AI-302 draft (released just a couple of days ago)
> > here:
> > 
> > http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-20302.TXT?rev=1.23
> 
> I noticed some syntax in the package specification of that link above,
> which is unfamiliar to me:
> 
>    procedure Update_Element
>      (Container : in out Vector;
>       Index     : in     Index_Type;
>       Process   : not null access procedure (Element : in out Element_Type));
> 
> What is meant by this "not null"?  Is this available in ADA95, or new
> to ADA05?

New to Ada 2005.  "Not null" means there's a run-time check that the
pointer is not null.  It's pretty annoying that in order to pass a
procedure as a parameter, you have to say the noise words "not null access",
but that was considered necessary for compatibility.

> I also had a more general question with access procedures.  Does an
> access procedure still have scope in the package it is defined in?
> Will it be able to access other subprograms and variables that it
> normally would, when it is executed by the container package,
> considering the container package has no visibility into its user?

Yes.  This is the "downward closure" feature that we've all been waiting
for.

- Bob