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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada and Unicode
Date: Mon, 19 Apr 2021 14:52:43 +0200
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On 2021-04-19 13:56, Luke A. Guest wrote:
> On 19/04/2021 10:08, Stephen Leake wrote:
>>> What's the way to manage Unicode correctly ?
>>
>> There are two issues: Unicode in source code, that the compiler must
>> understand, and Unicode in strings, that your program must understand.
> 
> And this is there the Ada standard gets it wrong, in the encodings 
> package re utf-8.
> 
> Unicode is a superset of 7-bit ASCII not Latin 1. The high bit in the 
> leading octet indicates whether there are trailing octets. See 
> https://github.com/Lucretia/uca/blob/master/src/uca.ads#L70 for the data 
> layout. The first 128 "characters" in Unicode match that of 7-bit ASCII, 
> not 8-bit ASCII, and certainly not Latin 1. Therefore this:
> 
> package Ada.Strings.UTF_Encoding
>    ...
>    subtype UTF_8_String is String;
>    ...
> end Ada.Strings.UTF_Encoding;
> 
> Was absolutely and totally wrong.

It is practical solution. Ada type system cannot express differently 
represented/constrained string/array/vector subtypes. Ignoring Latin-1 
and using String as if it were an array of octets is the best available 
solution.

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