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=-0.3 required=5.0 tests=BAYES_00, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 X-Google-Thread: a07f3367d7,73cb216d191f0fef X-Google-Attributes: gida07f3367d7,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII X-Received: by 10.180.182.229 with SMTP id eh5mr1243932wic.1.1364344207906; Tue, 26 Mar 2013 17:30:07 -0700 (PDT) Path: p18ni19764wiv.0!nntp.google.com!feeder1.cambriumusenet.nl!82.197.223.103.MISMATCH!feeder3.cambriumusenet.nl!feed.tweaknews.nl!193.141.40.65.MISMATCH!npeer.de.kpn-eurorings.net!npeer-ng0.de.kpn-eurorings.net!border2.nntp.ams2.giganews.com!border4.nntp.ams.giganews.com!border2.nntp.ams.giganews.com!border2.nntp.dca.giganews.com!nntp.giganews.com!newsgate.cuhk.edu.hk!goblin2!goblin.stu.neva.ru!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Is this expected behavior or not Date: Wed, 20 Mar 2013 14:21:09 +0100 Organization: cbb software GmbH Message-ID: <1xg9wka6slgit.1q0leacagdeuv.dlg@40tude.net> References: <7jct0noryc1v.1rnj5kkzx6m35.dlg@40tude.net> <5141c499$0$6642$9b4e6d93@newsspool2.arcor-online.net> <18r2kop6fyozu.tctrjnghfxqs.dlg@40tude.net> <1wv3p3nrtejfk$.bwebhg9agt0l.dlg@40tude.net> <514874d3$0$6628$9b4e6d93@newsspool2.arcor-online.net> <1o60gooo8xvba$.1ei9cebb07zek$.dlg@40tude.net> <514897bd$0$6641$9b4e6d93@newsspool2.arcor-online.net> <1oqwvcemo8dha$.hevuedtz8eze.dlg@40tude.net> <14aijp8ckzahf$.1ilfm1nw6qgyt$.dlg@40tude.net> Reply-To: mailbox@dmitry-kazakov.de NNTP-Posting-Host: FbOMkhMtVLVmu7IwBnt1tw.user.speranza.aioe.org Mime-Version: 1.0 X-Complaints-To: abuse@aioe.org User-Agent: 40tude_Dialog/2.0.15.1 X-Notice: Filtered by postfilter v. 0.8.2 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8bit Date: 2013-03-20T14:21:09+01:00 List-Id: On Wed, 20 Mar 2013 12:01:25 +0100, J-P. Rosen wrote: > Le 20/03/2013 11:04, Dmitry A. Kazakov a �crit : >>> It is different in that a subtype does NOT inherit operations, it has >>> the SAME operations as its type. >> >> How do you know that they are same? In what sense are they same? >> >> But they are evidently not same: >> >> procedure Foo (X : out Integer) is >> begin >> X := -1; >> end Foo; >> >> when inherited by Positive changes its behavior. > They are not inherited! You can call the above Foo with a variable of > type Positive; Constraint_Error is raised after the call when converting > back. But once again, it is the same operation that is called by Integer > and Positive. See, same operation applied to same value of same type gives different result. This is called UNTYPED. >>> Proof: a fundamental feature of OOP is that you can redefine inherited >>> operations. You cannot redefine operations of a subtype to be different >>> from those of its type. >> >> But they are redefined. The compiler adds conversion to the subtype for >> each in-argument and conversion from the subtype for each out-argument. >> Which is what happens with Foo above the body of >> >> procedure Foo (X : out Positive) >> >> is the body of >> >> procedure Foo (X : out Integer) + constraint check. >> > This is not the way it is defined in Ada, This is the way it works, so it is the way it is. > and what I said is that the > user cannot redefine Foo for Positive. Which was the core problem with the subtype Prime and the operation 'Succ the OP reported. Inheritance as-is composed with a conversion is relatively harmless when the constraint is a range. But when the constraint is arbitrary it would break almost everything and it does. This is a hard mathematical fact, no LRM or ISO has any authority here. >>> Note also that a subtype is a property of an object; a value has no >>> subtype, only a type. >> >> No, subtyping is a relation between two types, denoted as T<:S. > In standard OO speak yes, but that is NOT the meaning in Ada. The definition is independent on any language. I don't redefine the meaning of Ada-subtype. I translate Ada's definition into the terms of ADT. In these terms Ada-subtype is a proper type. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de