From: Victor Porton <porton@narod.ru>
Subject: Re: Subtypes and type invariants in Ada2012
Date: Mon, 21 Aug 2017 19:29:44 +0300
Date: 2017-08-21T19:29:44+03:00 [thread overview]
Message-ID: <onf1q0$bbm$1@gioia.aioe.org> (raw)
In-Reply-To: onf14l$9uv$1@gioia.aioe.org
Dmitry A. Kazakov wrote:
> 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.
I don't get. What do you mean saying "breaks"?
For me the condition Is_Prime added to a subtype of Natural seems quite
natural. It is quite natural to have a variable which can hold only prime
numbers. This may appear in some math software.
I would propose to add public subtype invariants (not only private tagged
type invariants as now) to Ada2020. Anything particular against this?
--
Victor Porton - http://portonvictor.org
next prev parent reply other threads:[~2017-08-21 16:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-21 15:38 Subtypes and type invariants in Ada2012 Victor Porton
2017-08-21 16:10 ` J-P. Rosen
2017-08-21 16:18 ` Dmitry A. Kazakov
2017-08-21 16:29 ` Victor Porton [this message]
2017-08-21 16:52 ` Dmitry A. Kazakov
2017-08-21 17:41 ` Victor Porton
2017-08-21 19:55 ` Dmitry A. Kazakov
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