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: a07f3367d7,66fae8c862b81b17
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,UTF8
Received: by 10.224.111.140 with SMTP id s12mr3064331qap.5.1351979848421;
        Sat, 03 Nov 2012 14:57:28 -0700 (PDT)
Received: by 10.52.76.136 with SMTP id k8mr906041vdw.13.1351979848396; Sat, 03
 Nov 2012 14:57:28 -0700 (PDT)
Path: 
 gf5ni18188417qab.0!nntp.google.com!c7no5159459qap.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Sat, 3 Nov 2012 14:57:28 -0700 (PDT)
In-Reply-To: <op.wm7f72j3ule2fv@cardamome>
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com;
 posting-host=46.171.80.166;
 posting-account=bMuEOQoAAACUUr_ghL3RBIi5neBZ5w_S
NNTP-Posting-Host: 46.171.80.166
References: <1aWdnbcg_8-BzAzNnZ2dnUVZ_j6dnZ2d@giganews.com>
 <k6rk3m$fu6$1@dont-email.me>
 <559eb706-9bb1-496d-9034-1984d693531a@googlegroups.com>
 <op.wm48fcpwule2fv@cardamome>
 <5460fdc7-5490-4889-b771-67cc281c10c5@googlegroups.com>
 <op.wm56yo11ule2fv@cardamome>
 <f37a66a6-3cca-4f4c-85ce-efb95ca4af57@googlegroups.com>
 <op.wm7fsuxjule2fv@cardamome> <op.wm7f72j3ule2fv@cardamome>
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <6260a796-83c4-4ce5-88cb-8249846bc035@googlegroups.com>
Subject: Re: Copy vector in Ada
From: Maciej Sobczak <see.my.homepage@gmail.com>
Injection-Date: Sat, 03 Nov 2012 21:57:28 +0000
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Date: 2012-11-03T14:57:28-07:00
List-Id: <comp.lang.ada>

W dniu sobota, 3 listopada 2012 17:03:33 UTC+1 u=C5=BCytkownik Hibou57 (Yan=
nick Duch=C3=AAne) napisa=C5=82:

> Some other words: I hardly believe an assignment operator could ever be O=
K =20
> within a context where the meaning of what an object is depends on whethe=
r =20
> it is used by value or reference (the truncation case Peter made me =20
> recall), and where there's nothing like proper class wide type, as C++ =
=20
> class wide behaviour also depends on whether an instance is used by value=
 =20
> vs by reference (always class wide with reference). Can you make an =20
> assignment operator works fine and uniformly in such circumstances?

No and I don't even intend to do it. Mixing assignment with polymorphism is=
 evil and cannot be implemented reasonably anyway. In the case of derivatio=
n hierarchy I would rather introduce the "clone" operation or something equ=
ivalent. Interestingly, in the hierarchy I would also ban the copying entir=
ely, which means that pass by copy becomes impossible and the whole problem=
 of uniformity just disappears.

Note that Ada does not provide any universal solution to this problem, eith=
er - assignment cannot be reasonably implemented apart from the case of mat=
ching tags, which introduces a run-time aspect to the whole; this is in con=
trast to banning assignment, which in terms of limitedness is always resolv=
ed statically.
It's a bit messy.

> The
> orthogonality C++ lacks here is a fact to be added to the particular poin=
t =20
> you raised.

Not much. In the case of derivation hierarchy, neither Ada nor C++ offer an=
ything useful (and that's OK as the concept is broken anyway). C++ does pro=
vide a cleaner solution for the case of non-dispatching assignment.

--=20
Maciej Sobczak * http://www.msobczak.com * http://www.inspirel.com