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=-0.9 required=5.0 tests=BAYES_00,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM autolearn=no 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!postnews.google.com!m36g2000hse.googlegroups.com!not-for-mail
From: Maciej Sobczak <see.my.homepage@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada Interfaces and the Liskov Substitution Principle
Date: 24 May 2007 00:29:29 -0700
Organization: http://groups.google.com
Message-ID: <1179991769.376381.252010@m36g2000hse.googlegroups.com>
References: <Pine.LNX.4.64.0705232101220.20072@th.informatik.uni-mannheim.de>
   <1179953657.839272.160320@a26g2000pre.googlegroups.com>
   <f32d9o$fi9$1@jacob-sparre.dk>
NNTP-Posting-Host: 137.138.37.241
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
X-Trace: posting.google.com 1179991776 6792 127.0.0.1 (24 May 2007 07:29:36
 GMT)
X-Complaints-To: groups-abuse@google.com
NNTP-Posting-Date: Thu, 24 May 2007 07:29:36 +0000 (UTC)
In-Reply-To: <f32d9o$fi9$1@jacob-sparre.dk>
User-Agent: G2/1.0
X-HTTP-UserAgent: Mozilla/5.0 (X11; U; Linux i686; en-US;
 rv:1.8.0.10) Gecko/20070228 Red Hat/1.5.0.10-0.1.slc3
 Firefox/1.5.0.10,gzip(gfe),gzip(gfe)
Complaints-To: groups-abuse@google.com
Injection-Info: m36g2000hse.googlegroups.com; posting-host=137.138.37.241;
   posting-account=Ch8E9Q0AAAA7lJxCsphg7hBNIsMsP4AE
Xref: g2news1.google.com comp.lang.ada:15898
Date: 2007-05-24T00:29:29-07:00
List-Id: <comp.lang.ada>

On 23 Maj, 23:58, "Randy Brukardt" <r...@rrsoftware.com> wrote:

> > My humble opinion: assignment of class-wide types should be prohibited
> > in the first place. I mean - at compile time.
> > It's just asking for troubles.
>
> That doesn't make much sense. Yes, it is a bit weird that assignment is
> potentially a dispatching operation, but otherwise there is no semantic
> problem with it.

Can it be dispatching on both arguments?
If not, how can you reasonably implement it?

And even if it could, still, how can you *reasonably* implement it?

Let's take a classic example with the hierarchy of geometric objects
(Object, Rectlangle, Triangle, Circle, and so on) and this:

procedure Do_Something(X : in Object'Class; Y : out Object'Class) is
begin
  Y := X; -- ?
end Do_Something;

> (The OP having an illegal example, thus proving nothing.)

The OP did not prove that Ada violates LSP, but he did point out where
the problems can hide.

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?

> It might be a bit hard to use usefully, but that's no reason for banning it.

C programmers can use the same logic to justify everything. ;-)

--
Maciej Sobczak
http://www.msobczak.com/