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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: issue with implementing a visitor design pattern
Date: Tue, 27 Jan 2004 09:36:20 +0100
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Date: 2004-01-27T09:36:20+01:00
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On 26 Jan 2004 15:18:41 -0500, Robert A Duff
<bobduff@shell01.TheWorld.com> wrote:

>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!

It is a strange thing, "when others". Especially when others (:-)) is
empty, like in:

subtype Empty is String (0..-1);
X : Empty := (others => ' ');

--
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de