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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Community Input for the Maintenance and Revision of the Ada
 Programming Language
Date: Thu, 31 Aug 2017 11:52:01 +0200
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Xref: news.eternal-september.org comp.lang.ada:47851
Date: 2017-08-31T11:52:01+02:00
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On 31/08/2017 09:36, Jacob Sparre Andersen wrote:
> Robert Eachus wrote:
> 
>> There is an 'elegant' solution.  Add a UTF8 character string type.
> 
> Wouldn't it be more elegant to redefine Character to cover all Unicode
> code-points?  (And make Wide_Character and Wide_Wide_Character renamings
> (i.e. subtypes) of Character.)  The Latin-N character sets will of
> course have to be declared as subtypes of Character, and I/O
> serialization will have to be told of character encodings.
> 
> I can imagine that there may be some incompabilities from making such a
> change, but what are they?

You need a view of a string as an array of code points / unicode 
characters *and* another view as an array of encoding items, e.g. octet 
for UTF-8 or word for UTF-16 etc.

UTF-16 and UTF-8 strings are equivalent types in the view of code point 
arrays. UCS-2 is a constrained subtype of both. ASCII string is a 
constrained subtype of any.

In the second view ASCII string is a subtype of only UTF-8 string. It is 
an unrelated type to UCS-2 and UTF-16.

You cannot handle this in present Ada.

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