From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.5-pre1 (2020-06-20) on ip-172-31-74-118.ec2.internal X-Spam-Level: X-Spam-Status: No, score=-1.9 required=3.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.5-pre1 Path: eternal-september.org!reader02.eternal-september.org!maths.tcd.ie!nntp-feed.chiark.greenend.org.uk!ewrotcd!nntp.terraraq.uk!aioe.org!5WHqCw2XxjHb2npjM9GYbw.user.gioia.aioe.org.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Ada and Unicode Date: Mon, 19 Apr 2021 15:31:28 +0200 Organization: Aioe.org NNTP Server Message-ID: References: <607b5b20$0$27442$426a74cc@news.free.fr> <86mttuk5f0.fsf@stephe-leake.org> NNTP-Posting-Host: 5WHqCw2XxjHb2npjM9GYbw.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; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 X-Notice: Filtered by postfilter v. 0.9.2 Content-Language: en-US Xref: reader02.eternal-september.org comp.lang.ada:61846 List-Id: On 2021-04-19 15:15, Luke A. Guest wrote: > On 19/04/2021 14:10, Dmitry A. Kazakov wrote: > >>> They're different types and should be incompatible, because, well, >> they are. What does Ada have that allows for this that other languages >> doesn't? Oh yeah! Types! >> >> They are subtypes, differently constrained, like Positive and Integer. > > No they're not. They're subtypes only and therefore compatible. The UTF > string isn't constrained in any other ways. Of course it is. There could be string encodings that have no Unicode counterparts and thus missing in UTF-8/16. >> Operations are same values are differently constrained. It does not >> make sense to consider ASCII 'a', Latin-1 'a', UTF-8 'a' different. It >> is same glyph differently encoded. Encoding is a representation >> aspect, ergo out of the interface! > > As I already said in Unicode the glyph is not part part of Unicode. The > single code point character concept doesn't exist anymore. It does not matter from practical point of view. Some Unicode's idiosyncrasies are better ignored. >> BTW, subtype is a type. > subtype is a compatible type. Ada subtype is both a sub- and supertype, i.e. substitutable [or so the compiler thinks] in both directions. A derived tagged type is substitutable in only one direction. Neither is fully "compatible", because otherwise there would be no reason to have an exactly same thing. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de