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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Concatenate enumeration
Date: Fri, 12 Nov 2010 11:55:34 -0600
Organization: Jacob Sparre Andersen
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Date: 2010-11-12T11:55:34-06:00
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"okellogg" <okellogg@users.sourceforge.net> wrote in message 
news:0ff42bdb-63a1-4fc2-bb44-e8d89a82bc68@j18g2000yqd.googlegroups.com...
> In 
> https://groups.google.com/group/comp.lang.ada/browse_thread/thread/33ce43bfeafb2681/237f979efee731d3,
> Randy Brukardt wrote:
>
>> "Robert A Duff" <bobd...@shell01.TheWorld.com> wrote in message
>> news:wcctywksu8t.fsf@shell01.TheWorld.com...
>> ...
>>
>> >> You can't. Enumeration types are not extensible.
>>
>> > Extensible enumeration types were proposed for Ada 9X,
>> > but were dropped.
>>
>> And were proposed again for Ada 2005, and were dropped again. See
>> AI95-0261-1. I doubt it will ever be proposed again.
>
> I wonder why this has not been picked up - especially when looking at
> all the new features that are making it into Ada2012.

The semantic difficulties are staggering. It just doesn't make sense in the 
Ada model of types (mostly because of the Ada requirement that enumerations 
be elementary types). Some solution to the problems probably could be found, 
but the obvious ones make the extensions near useless. Go read AI95-0261-1 
if you care about the details.

                                         Randy.