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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada.Locales pseudo-string types
Date: Wed, 8 Aug 2012 10:35:01 +0200
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Date: 2012-08-08T10:35:01+02:00
List-Id: <comp.lang.ada>

On Wed, 08 Aug 2012 11:17:46 +0300, Niklas Holsti wrote:

> For value conversions, including "in" parameters, the exact match could
> be replaced by a static check that the constraints on the source
> elements are the same as or stronger than those on the target elements.
> This would allow Ada.Text_IO.Put (String (Some_Country_Code)).
> 
> For "out" parameters, there could be a static check that the constraints
> on the actual (source) array elements are the same as or weaker than
> those on the formal (target) array elements.
> 
> For "in out" parameters, the present static-match rule would be kept, as
> the logical conjunction of the "in" and "out" rules.

1. You cannot check that statically because the constraint of the subtype
can be dynamic.

2. It is extremely uncomfortable to have legality dependant on the
constraint and the parameter mode. It is worse than just inference it is in
effect weakly typing.

I don't want repeating the discussing about dynamic contracts, but this is
exactly same issue. You either not allow this, or else you add
Constraint_Error to all contracts. There is no sane middle way.

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