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-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,4687ad82921cf6ad
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2004-01-26 12:18:42 PST
Path: 
 archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsswitch.lcs.mit.edu!nntp.TheWorld.com!not-for-mail
From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: issue with implementing a visitor design pattern
Date: 26 Jan 2004 15:18:41 -0500
Organization: The World Public Access UNIX, Brookline, MA
Message-ID: <wccllnubh0e.fsf@shell01.TheWorld.com>
References: <100dqeul3pqiua0@corp.supernews.com>
 <OdKdnWfUk9xjM5XdRVn-gg@comcast.com> <wccr7xyfeu3.fsf@shell01.TheWorld.com>
 <MrNoSpam-AA0930.07381425012004@news-server.bigpond.net.au>
 <wcc4qult42l.fsf@shell01.TheWorld.com>
 <sjj910dp4afg8eprr0is06943dgp2cphh6@4ax.com>
NNTP-Posting-Host: pip1-5.std.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: pcls4.std.com 1075148322 22228 192.74.137.185 (26 Jan 2004 20:18:42
 GMT)
X-Complaints-To: abuse@TheWorld.com
NNTP-Posting-Date: Mon, 26 Jan 2004 20:18:42 +0000 (UTC)
User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2
Xref: archiver1.google.com comp.lang.ada:4835
Date: 2004-01-26T15:18:41-05:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> writes:

> On 24 Jan 2004 16:44:02 -0500, Robert A Duff
> <bobduff@shell01.TheWorld.com> wrote:
> 
> >Dale Stanbrough <MrNoSpam@bigpoop.net.au> writes:
> >
> >> Robert A Duff wrote:
> 
> >Adding "case on 'Tag" to Ada would not be trivial.  One would have to
> >reconcile the open-ended type extension capability of tagged types with
> >the full-coverage rules of case statements.
> 
> Same as with integer types, an obligatory:
> 
>    when others =>
>       ...

"when others" *defeats* the full-coverage rules.  It should be used only
if you know it covers *all* the other cases, including the ones that
haven't been invented yet!

> Then, of course, there could be subtypes of classes and thus finite
> sets of tags:

Maybe...

- Bob