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 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: function Is_Open (File : File_Type) return Boolean; :Text_io Date: Tue, 27 Oct 2015 21:04:19 +0100 Organization: cbb software GmbH Message-ID: <1dzlgoh4u2j7t$.1un3dfy0oeigd$.dlg@40tude.net> References: <87twpd2qlo.fsf@theworld.com> <1pj15r7pul7f1.15qgdyrc8k133$.dlg@40tude.net> <87pp0030c1.fsf@theworld.com> <135hiczk56x02.1xixcme8btbl4.dlg@40tude.net> Reply-To: mailbox@dmitry-kazakov.de NNTP-Posting-Host: j6IQVb9uobzjXrpQLDU2rQ.user.speranza.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: 40tude_Dialog/2.0.15.1 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:28083 Date: 2015-10-27T21:04:19+01:00 List-Id: On Tue, 27 Oct 2015 17:43:36 +0100, G.B. wrote: > On 27.10.15 16:26, Dmitry A. Kazakov wrote: >> How do you know if some callers would not appreciate Status_Error as >> a possible outcome? > > Actually, this situation is what contracts are made for, > I think: > as a caller, you say what you want the procedure to do, > or else you don't sign this contract. I.e., a redesign > via ECR is in order before you sign. Sure, except that you don't subscribe the contract you cannot fulfill. The point can be summarized this way. If an exception is a part of the contract then Status_Error is much better than Constraint_Error and is already there. If the contract is not to raise, then, firstly, there is no way to enforce it, and, secondly, if there were a way, proving no Status_Error would be no harder than no Constraint_Error. Ergo, no use. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de