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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Array conversion and bounds
Date: Sun, 15 Apr 2018 16:11:27 +0300
Organization: Tidorum Ltd
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Xref: reader02.eternal-september.org comp.lang.ada:51512
Date: 2018-04-15T16:11:27+03:00
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On 18-04-15 15:34 , Dmitry A. Kazakov wrote:
> On 2018-04-15 12:37, Niklas Holsti wrote:
>> On 18-04-15 12:36 , Dmitry A. Kazakov wrote:
>>> Do array bounds slide during conversion? Consider this:
>>>
>>>    type A is array (Integer range <>) of Whatever;
>>>    type B is array (Unsigned_32 range <>) of Whatever;
>>>
>>>    X : A (-10..-1);
>>>    Y : B (1..10);
>>> begin
>>>    Y := B (X); -- Is this OK?
>>>
>>> If bounds slide it must be OK, if bounds do not slide, it must raise
>>> Constraint_Error.
>>>
>>> Any language lawyers?
>>
>> I believe the bounds should _not_ slide, because the "target subtype"
>> of the conversion is type B, which is an _unconstrained_ array subtype.
>
> Better to say, they should, but they do not.

Ok, if I read the RM correctly (and you seem to agree with me) they "do 
not" slide when the target subtype is unconstrained.

> Clearly conversions like this should not require resorting to
> Unchecked_Conversion.

Is there some reason why you cannot use the constrained-target-subtype 
method to force sliding?

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .