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 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: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Bug in Ada - Latin 1 is not a subset of UTF-8 Date: Tue, 18 Oct 2016 22:03:13 +0200 Organization: Aioe.org NNTP Server Message-ID: References: <86f0d2fe-d498-4bc4-bb9d-e34629c89bb4@googlegroups.com> NNTP-Posting-Host: XXXaKfQ6zzC8DMOzOT/pgA.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:32127 Date: 2016-10-18T22:03:13+02:00 List-Id: On 2016-10-18 19:35, G.B. wrote: > On 18.10.16 18:35, Dmitry A. Kazakov wrote: >> No invariant can make Latin-1 A-umlaut UTF-8 A-umlaut. > > Who would ever want to do that? Somebody claiming that UTF-8 string is a constrained subtype of Latin-1 string. > To get a subset U from a set S, you apply a constraint > to S. That's not (easily) expressible in Ada in this case. There is no such constraint at all. A-umlaut in Latin-1 is one character, in UTF-8 it is two characters. To introduce a subtype relationship we need a conversion, not a constraint. Ada does not support this method of subtype construction. > But if it is, with the help of a predicate, the we can > say that UTF_8_String is-a "constrained" String because > their sets are. They are not, as demonstrated on the example of A-umlaut. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de