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=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news3.google.com!feeder.news-service.com!feeder.news-service.com!newsfeed-fusi2.netcologne.de!195.14.215.230.MISMATCH!news.netcologne.de!newsfeed-hp2.netcologne.de!newsfeed.arcor.de!newsspool4.arcor-online.net!news.arcor.de.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada vs Eiffel - Ada programmer approach
Newsgroups: comp.lang.ada
User-Agent: 40tude_Dialog/2.0.15.1
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Reply-To: mailbox@dmitry-kazakov.de
Organization: cbb software GmbH
References: 
 <405b5054-4c8f-4e16-9ea8-503a9b9f976e@t21g2000yqi.googlegroups.com>
 <4A19765C.608@obry.net>
 <8105b65f-4de9-4653-b43a-d55ee33f072d@k2g2000yql.googlegroups.com>
 <a924d96e-17b8-4573-ae86-3ccc924d21c8@x6g2000vbg.googlegroups.com>
 <88f38fe3-01ec-407f-b7b6-84a1d10de7f1@h11g2000yqb.googlegroups.com>
 <wccws7s166w.fsf@shell01.TheWorld.com> <878wk299uj.fsf@willow.rfc1149.net>
 <wccvdn6a55g.fsf@shell01.TheWorld.com> <h0k4o9$e37$1@munin.nbi.dk>
Date: Tue, 9 Jun 2009 09:39:51 +0200
Message-ID: <1jyf6p60hv1n4$.1pavbtr5qwfnz$.dlg@40tude.net>
NNTP-Posting-Date: 09 Jun 2009 09:39:51 CEST
NNTP-Posting-Host: 194426cf.newsspool2.arcor-online.net
X-Trace: 
 DXC=c;h4J@GijjcfF8a^:6>b7eA9EHlD;3Ycb4Fo<]lROoRa^YC2XCjHcbi:D]QH12R7@eDNcfSJ;bb[eFCTGGVUmh?dLK[5LiR>kgboP>HcSFVJ2i
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news2.google.com comp.lang.ada:6386
Date: 2009-06-09T09:39:51+02:00
List-Id: <comp.lang.ada>

On Mon, 8 Jun 2009 17:52:27 -0500, Randy Brukardt wrote:

> "Robert A Duff"  writes:
> ...
>> An invariant (whether it be a pragma, or some special syntax) would be
>> attached to a type, and would mean "all objects of this type have
>> this property, always" (except that maybe objects can temporarily
>> violate their invariant, so long as the code puts it back).
>>
>> A related concept that has been discussed is "user-defined constraints".
>> I'm not sure what the difference is, exactly -- I think with user-defined
>> constraints, you can't "temporarily violate".
> 
> A user-defined constraint applies to a view (usually via a subtype), while 
> an invariant applies to a type (always).

I do not see any difference. Invariant is merely a private constraint.
User-defined constraint is a [public] part of the invariant.

> For instance, a user-defined 
> constraint can apply to a formal parameter but not to the actual parameter 
> object (just as any other constraint).

Hmm, I think this confuses constraints put on a type/subtype with
discriminants of an object. Obviously, any combination of discriminants'
values determine some anonymous subtype with a corresponding invariant.
That is an invariant of the object only in the sense that the object has
this anonymous subtype. Objects do not have invariants.

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