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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Is this expected behavior or not
Date: Tue, 12 Mar 2013 10:17:37 +0100
Organization: cbb software GmbH
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Date: 2013-03-12T10:17:37+01:00
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On Mon, 11 Mar 2013 16:01:04 -0400, Robert A Duff wrote:

> Anh Vo <anhvofrcaus@gmail.com> writes:
> 
>> I have read ARM section 3.2.4, Subtype Predicates, I did not see any
>> rules prohibiting from using attribute 'Succ as contained in the code
>> nipet below. I would expect Prime'Succ (3) return 5 for next prime
>> number. However, 4 is returned instead. Is this a correct behavior?
> 
> It is standard-conforming behavior.  Prime'Succ is the same as
> Prime'Base'Succ.

Is the profile same? Let S be a subtype of T, then is 'Succ contravariant
in the result? E.g.

   function "'Succ" (X : S) return T'Base;

for any subtype. Or it is just an erroneous inheritance of the base
operation for fully covariant

   function "'Succ" (X : S) return S;

Or, maybe, it is not even covariant in the argument. Which might be the
case. Considering

   Prime'Succ (2)

If 'Succ is convariant in the argument, this shall raise Constraint_Error
because 2 is not Prime.

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