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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: class wide iterable (and indexable)
Date: Mon, 28 Jan 2019 18:23:08 +0100
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Xref: reader01.eternal-september.org comp.lang.ada:55390
Date: 2019-01-28T18:23:08+01:00
List-Id: <comp.lang.ada>

On 2019-01-28 16:54, Shark8 wrote:
> On Wednesday, January 23, 2019 at 3:47:43 PM UTC-7, Randy Brukardt wrote:
>> "Shark8" wrote in message
>> news:9eedf818-8bfb-465b-afe5-aa3fb0525948...
>>> Wouldn't this be a non-issue if we could Static_Predicate Array-types like
>>> so?
>>>
>>> Type Some_String is Array(Positive range <>) of Character
>>>   with Static-Predicate => Some_String'First = 1;
>>
>> The idea of a static predicate is for them to stand-in for proper set
>> constraints (I would have preferred the latter, but I was alone on that), so
>> they don't have anything to do with array bounds.
> 
> What do you mean by "proper set constraints"? [And how would they look?]
> Things like {x| x in {2**y where y in 0..15} }? (X in 1|2|4|8|16|..|32_768)

Certainly not an arbitrary constraint. The problem is with the 
operations, i.e. with substitutability. Constraining should not violate 
much of it and the user must known what gets broken. An arbitrary 
constraint breaks pretty much everything and you have no idea which 
operations still work. Ada's range constraint breaks a limited number of 
things and many of these breaks can be statically checked.

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