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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Subtypes and type invariants in Ada2012
Date: Mon, 21 Aug 2017 18:18:27 +0200
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Date: 2017-08-21T18:18:27+02:00
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On 2017-08-21 17:38, Victor Porton wrote:

> So, my question: Is it possible to restrict a subtype with something like a
> type invariant?

Type invariant is not a restriction of public interface/properties, it 
is an implementation detail. So it should never produce a [sub]type.

> I want a subtype restricted by an arbitrary condition. Is it possible?

Arbitrary condition breaks type operations. E.g. condition Is_Prime (X) 
breaks more or less everything (assuming covariance). All restrictions 
do. A few don't break much, e.g. range constraints.

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