From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=ham autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII
X-Google-Thread: 103376,fea5f9c57f8bf287
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2001-10-20 12:02:04 PST
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!fr.clara.net!heighliner.fr.clara.net!proxad.net!feeder2-1.proxad.net!news.free.fr!not-for-mail
Message-ID: <3BD1CAC0.F5F48B14@free.fr>
Date: Sat, 20 Oct 2001 21:04:32 +0200
From: Damien Carbonne <damien.carbonne@free.fr>
X-Mailer: Mozilla 4.75 [fr] (X11; U; Linux 2.2.17-21mdk i686)
X-Accept-Language: en
MIME-Version: 1.0
Newsgroups: comp.lang.ada
Subject: Re: Discriminants constraining unconstrained array types
References: <87g08e9urn.fsf@chiark.greenend.org.uk>
 <3BD1B6F3.F90883D7@worldnet.att.net>
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
NNTP-Posting-Date: 20 Oct 2001 21:02:04 MEST
NNTP-Posting-Host: 213.228.10.35
X-Trace: 1003604524 news1-1 859 213.228.10.35
Xref: archiver1.google.com comp.lang.ada:14973
Date: 2001-10-20T21:02:04+02:00
List-Id: <comp.lang.ada>

James Rogers a �crit :

> Matthew Woodcraft wrote:
> >
> > The following rule appears in the GNAT coding style guide:
> >
> > | Do not declare discriminated record types where the discriminant is
> > | used for constraining an unconstrained array type. (Discriminated
> > | records for a variant part are allowed.)
> >
> > Does anyone know a reason to avoid this feature of the language in
> > general, or is it more likely that there's just some issue with the
> > runtime or bootstrap behaviour which makes it inadvisable to use in the
> > compiler itself?
>
> I was not involved in the team that wrote this guideline.
>
> I can explain some of the problems with declaring discriminated
> record types used for constraining unconstrained array types.
>
> The first problems is memory usage. Take the following example:
>
> type Unconstrained_Type is array(Positive range <>) of Integer;
>
> type Inadvised_Record_Type (Max : Positive) is record
>    Buffer : Unconstrained_Type(1..Max);
> end record;
>

I think what you explain further is right only if the declaration was:

type Inadvised_Record_Type (Max : Positive :=  1) is record
   Buffer : Unconstrained_Type(1..Max);
end record;

Note: "1" could be replaced by any other valid value.
The issue is with default values and declarations without constraint.