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 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,2ff5c149712ec0eb
X-Google-Attributes: gid103376,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news3.google.com!out02a.usenetserver.com!news.usenetserver.com!in04.usenetserver.com!news.usenetserver.com!feed.cgocable.net!meganewsservers.com!feeder2.on.meganewsservers.com!195.62.97.14.MISMATCH!newsfeed0.kamp.net!newsfeed.kamp.net!213.239.142.2.MISMATCH!feed.xsnews.nl!border-1.ams.xsnews.nl!tudelft.nl!txtfeed1.tudelft.nl!feeder1.cambrium.nl!feed.tweaknews.nl!news.netcologne.de!nhp.netcologne.de!newsfeed.arcor.de!newsspool3.arcor-online.net!news.arcor.de.POSTED!not-for-mail
Newsgroups: comp.lang.ada
Subject: Re: Ada Interfaces and the Liskov Substitution Principle
From: Georg Bauhaus <rm.tsoh+bauhaus@maps.futureapps.de>
In-Reply-To: <12h6mi42jcha0.7f9vfsnihjwr$.dlg@40tude.net>
	 <Pine.LNX.4.64.0705232101220.20072@th.informatik.uni-mannheim.de>
	 <1179953657.839272.160320@a26g2000pre.googlegroups.com>
	 <f32d9o$fi9$1@jacob-sparre.dk>
	 <1179991769.376381.252010@m36g2000hse.googlegroups.com>
	 <12h6mi42jcha0.7f9vfsnihjwr$.dlg@40tude.net>
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
Message-Id: <1180003336.1163.29.camel@kartoffel>
Mime-Version: 1.0
X-Mailer: Evolution 2.10.1 
Date: Thu, 24 May 2007 12:42:16 +0200
Organization: Arcor
NNTP-Posting-Date: 24 May 2007 12:42:12 CEST
NNTP-Posting-Host: ff1f7dbd.newsspool3.arcor-online.net
X-Trace: 
 DXC=oo8^c^DCDB8L2C_`koXfC5McF=Q^Z^V384Fo<]lROoR1Fl8W>\BH3Y2gAH8R8U>S\?N[W<lHX`=B4\6BhD5G6\i<Z^nDGkbKSD=
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:15901
Date: 2007-05-24T12:42:12+02:00
List-Id: <comp.lang.ada>

On Thu, 2007-05-24 at 10:02 +0200, Dmitry A. Kazakov wrote:

> > Coming from C++, I have never seen any single example where assignment
> > made sense with polymorphic hierarchies.
...
> 
> > Do you know any such example? Can you show it?
> 
> Marshaling objects.

In fact, Eiffel has a relative, the assignment attempt
(written "?="). And the Eiffel arguments versus Liskov/Wing
are that the principles guiding program design should come
from the solution to a problem, not from models when these
cannot capture the solution. In a sense, it is argued that
that L/W substitution (and also co/contra-variance) violate
programming principles!

For example, you can make a primitive operation abstract
("deferred", "take it away") in a derived type. This might
make sense when for some good reasons, a *real* *world* heir
cannot
(a) have the inherited operation
(b) change its parents.