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From: Jacob Sparre Andersen <jacob@jacob-sparre.dk>
Newsgroups: comp.lang.ada
Subject: Re: Community Input for the Maintenance and Revision of the Ada
 Programming Language
Date: Sat, 12 Aug 2017 20:29:18 +0200
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:47718
Date: 2017-08-12T20:29:18+02:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov wrote:

>>     type May_Be_Integer(Valid: Boolean := True) is constant record
>>       case Valid is
>>      when True  => Value: Integer;
>>      when False => null;
>>       end case;
>>     end record;
>
> Hmm, isn't it simply a subtype:
>
>    type May_Be_Integer (Valid: Boolean := True) is record
>       case Valid is
>          when True =>
>             Value : Integer;
>          when False =>
>             null;
>       end case;
>    end record;
>
>    subtype Surely_Integer is May_Be_Integer (True);

No.  "constant" must mean that both "Valid" and "Value" are immutable.

I'm not sure why we should need constant/immutable types, but I'm open
to learn.

Greetings,

Jacob
-- 
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