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=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: class wide iterable (and indexable)
Date: Tue, 22 Jan 2019 09:56:50 +0100
Organization: Aioe.org NNTP Server
Message-ID: <q26lsh$1ee3$1@gioia.aioe.org>
References: <b5c56fdb-94d0-4930-952c-7754ec5dd729@googlegroups.com>
 <lyo98z558g.fsf@pushface.org>
 <2a6929c5-72fa-4d84-953a-44ea4597ab38@googlegroups.com>
 <q0m3u6$t9c$1@franka.jacob-sparre.dk>
 <f62bb15c-ebd2-45f7-b591-796a1957e99a@googlegroups.com>
 <q0n6av$1tqs$1@gioia.aioe.org> <q0psvi$v1q$1@franka.jacob-sparre.dk>
 <q0pvlp$1vp1$1@gioia.aioe.org> <q10f1v$v9r$1@franka.jacob-sparre.dk>
 <q11rqe$dtn$1@gioia.aioe.org> <q13biq$nle$1@franka.jacob-sparre.dk>
 <q159mg$1q6k$1@gioia.aioe.org> <q160mb$863$1@franka.jacob-sparre.dk>
 <q1715k$1fou$1@gioia.aioe.org> <q18g50$86r$1@franka.jacob-sparre.dk>
 <q19mh2$19lu$1@gioia.aioe.org> <q1j489$oo8$1@franka.jacob-sparre.dk>
 <q1k9ep$aku$1@gioia.aioe.org>
 <75328dc5-fc59-4228-b77e-77ba6e5101c3@googlegroups.com>
 <q25jpn$jfu$1@franka.jacob-sparre.dk>
NNTP-Posting-Host: MyFhHs417jM9AgzRpXn7yg.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.4.0
Content-Language: en-US
X-Notice: Filtered by postfilter v. 0.8.3
Xref: reader01.eternal-september.org comp.lang.ada:55322
Date: 2019-01-22T09:56:50+01:00
List-Id: <comp.lang.ada>

On 2019-01-22 00:15, Randy Brukardt wrote:
> For instance, in a Vector, the
> lower bound is fixed for all values of a particular type. That would
> eliminate a lot of programming errors that happen in Ada programs (many
> programs fail to deal with unusual lower bounds, because it's hard to get
> right).

I disagree. It would make array slices more difficult to use. Presently 
we can do things like

    Read (Buffer (From..To), Last);

Foo can move the index Last and this is the same index as outside in the 
caller because indices do not slide. If you make the lower bound fixed, 
indices would slide and that would require a lot of index arithmetic 
upon calling subprograms on slices. This would be far more error-prone 
than occasionally forgetting to use Buffer'First instead of 1.

P.S. If we wanted safety we could use private numeric types for array 
indices and alternative array constructors with the number of elements 
(universal integer) instead of a range. That would preclude any literals 
appearing in place of an index.

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