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!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: Victor Porton Newsgroups: comp.lang.ada Subject: A bad counterintuitive behaviour of Ada about OO Date: Tue, 05 Aug 2014 23:09:40 +0300 Organization: Aioe.org NNTP Server Message-ID: NNTP-Posting-Host: AnnUDmZwVERVUXyHDyOl5A.user.speranza.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/4.12.4 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:21461 Date: 2014-08-05T23:09:40+03:00 List-Id: http://freesoft.portonvictor.org/binaries/ada-obj-test.tar.gz contains a tiny Ada program which prints 0 despite intuition suggests that it should print 123, because it just copies (using Adjust) an object holding 123. In this program Handle_Type models some handle provided by an external API, where 0 is an undefined handle. Base_Object is a tagged record which holds a handle inside itself and can copy or destroy the handle automatically (as Base_Object is a controlled object). Example_Record is a derived type of Base_Object which imitates a behavior of a simple library which operates over some handles. For example, in this example copying a handle preserves it unchanged. This tiny program was created by me as a model of my real Ada bindings for Raptor C library, which produces a wrong behavior. Why Ada behaves in this counter-intuitive way? What should I do in similar situations when developing real Ada software? -- Victor Porton - http://portonvictor.org