From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: Victor Porton Newsgroups: comp.lang.ada Subject: Re: Subtypes and type invariants in Ada2012 Date: Mon, 21 Aug 2017 19:29:44 +0300 Organization: Aioe.org NNTP Server Message-ID: References: NNTP-Posting-Host: I58n5mqJebgcOFNDKXkBJw.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Complaints-To: abuse@aioe.org User-Agent: KNode/4.14.10 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:47769 Date: 2017-08-21T19:29:44+03:00 List-Id: 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