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-Thread: 103376,29d8139471e3f53e
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!news3.google.com!feeder.news-service.com!newsfeed.straub-nv.de!news-2.dfn.de!news.dfn.de!news.uni-stuttgart.de!news.belwue.de!newsfeed.arcor.de!newsspool3.arcor-online.net!news.arcor.de.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Preventing type extensions
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: <87iq2bfenl.fsf@mid.deneb.enyo.de>
 <874odv9npv.fsf@ludovic-brenta.org> <87y6b7cedd.fsf@mid.deneb.enyo.de>
 <66a3704c-54f9-4f04-8860-aa12f516134b@t3g2000vbb.googlegroups.com>
 <87d3sib44t.fsf@mid.deneb.enyo.de>
 <134q4k2ly2pf4$.17nlv1q6q5ivo.dlg@40tude.net>
 <4c8dec8e$0$6990$9b4e6d93@newsspool4.arcor-online.net>
Date: Mon, 13 Sep 2010 11:42:38 +0200
Message-ID: <epkb3s8dfxk0$.1qdvo5vg2fsgh.dlg@40tude.net>
NNTP-Posting-Date: 13 Sep 2010 11:42:39 CEST
NNTP-Posting-Host: de815430.newsspool2.arcor-online.net
X-Trace: 
 DXC=MlIoAf0T7HnIkjb;<8iR=aA9EHlD;3Ycb4Fo<]lROoRa8kF<OcfhCOk6LmHB:n:C5f[6LHn;2LCVn7enW;^6ZC`d\`mfM[68DCco6\4NRo0RNh
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:14036
Date: 2010-09-13T11:42:39+02:00
List-Id: <comp.lang.ada>

On Mon, 13 Sep 2010 11:19:10 +0200, Georg Bauhaus wrote:

> Reasons against extensibility just point to a very real phenomenon,
> that of (mis)trust among the members of a group relevant to the program/
> library: these include programmers, managers, sales personnel, users...
> Will they trust the currently known programmers, trust future colleagues,
> to use the extensible O-O library only in ways, say, covered by the
> legal contract from year X?  (Hint: viral callbacks.)

Mistrust in what? To give some terms:

type extension = aggregation of an instance + delegation to the operations
of the instance.

What is here not to trust? Aggregation? Delegation?

As for callbacks, I don't understand your note. My point was that
re-dispatch is the problem, not aggregation or delegation. Don't implement
anything by means of re-dispatch and you will have no "callbacks." A type
extension cannot break anything in the parent's implementation unless it
re-dispatches.

> If a system must reflect trust and mistrust, shouldn't the
> mechanics of a language support both?

In Ada it is called visibility.

> And hence---given the split
> between Ada's non-tagged and tagged types---shouldn't the langauge
> support "final" types?

This split was a pragmatic decision, to be fixed (removed) some day.

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