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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Bug in Ada - Latin 1 is not a subset of UTF-8
Date: Thu, 20 Oct 2016 09:36:31 +0200
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Date: 2016-10-20T09:36:31+02:00
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On 20/10/2016 02:31, Randy Brukardt wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:nu4nee$18le$1@gioia.aioe.org...
> ...
>> Numeric character is a constraint expressible in Ada:
>>
>>    subtype Numeric is Character range '0'..'9';
>>
>> Numeric string constraint is not expressible, but it still a constraint.
>
> It's expressible as a predicate, though; that's the entire point of
> predicates (to act like user-defined constraints):
>
>     subtype Numeric_String is String
>         with Dynamic_Predicate => (for all E of Numeric_String => E in
> Numeric);
>
> It's not 100% as good as a constraint (as modifications of individual
> components won't be checked), but it almost always will do the job.

Not nice. Is there a reason why, apart from premature optimization?

> You also could declare a new type with the proper constraint:
>     type Numeric_String is array (Positive range <>) of Numeric;
>
> That will have all of the string operations, but it (unfortunately) can't be
> converted to String (you'd have to write a function to do that).
>
> Since both of these possibilities exist, I'd hardly call the constraint "not
> expressible". At worst, it's inconvinient to express it.

Yes, maybe.

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