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: 103376,703c4f68db81387d X-Google-Thread: 109fba,703c4f68db81387d X-Google-Thread: 115aec,703c4f68db81387d X-Google-Thread: f43e6,703c4f68db81387d X-Google-Attributes: gid103376,gid109fba,gid115aec,gidf43e6,public X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!news.glorb.com!news.banetele.no!w3bhost.de!feeder.xsnews.nl!feeder.news-service.com!post.news-service.com!news1.surfino.com!not-for-mail Message-Id: <1531922.sRsIxUZLL9@linux1.krischik.com> From: Martin Krischik Subject: Re: [OT] Re: Teaching new tricks to an old dog (C++ -->Ada) Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng Reply-To: martin@krischik.com Date: Sat, 12 Mar 2005 19:40:28 +0100 References: <4229bad9$0$1019$afc38c87@news.optusnet.com.au> <1110032222.447846.167060@g14g2000cwa.googlegroups.com> <871xau9nlh.fsf@insalien.org> <3SjWd.103128$Vf.3969241@news000.worldonline.dk> <87r7iu85lf.fsf@insalien.org> <1110052142.832650@athnrd02> <42309456$1@news.broadpark.no> <1110569032.207770@athnrd02> <1110607809.837000@athnrd02> <1110608948.651588@athnrd02> <1110609321.686344@athnrd02> <1136ao15lb0go9c@corp.supernews.com> Organization: None User-Agent: KNode/0.8.0 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7Bit X-Complaints-To: abuse@surfino.com NNTP-Posting-Host: 83.169.175.19 (83.169.175.19) NNTP-Posting-Date: Sat, 12 Mar 2005 20:00:16 +0100 X-Trace: 00a0e42333c40f60c0ab609864 Xref: g2news1.google.com comp.lang.ada:9247 comp.lang.c++:45319 comp.realtime:1380 comp.software-eng:4943 Date: 2005-03-12T19:40:28+01:00 List-Id: CTips wrote: > REH wrote: > >> "Ioannis Vranos" wrote in message >> news:1110609321.686344@athnrd02... >> >> >>>>Myself thinks though that this whole range specialisation thing is >>>>non-sense for regular application programming at least. >>> >>> >>>Indeed. :-) >>> >>> >> >> Not all of us do "regular application programming." I write >> mission-critical systems. In such an environment, it is non-sense NOT to >> define ranges for data types that have them. I would rather it "failed >> loudly" when a variable strayed out of range and raised an exception I >> can recover from, then continuing to run, causing unknown or undefined >> behavior. >> > > Thats another problem with Ada's run-time checking. If you're using it > in an environment where the hardware may "fail" [e.g. alpha particles > randomizing memory], the checks are quite often in the wrong place. > > For example, look at the Ada equivalent of the following code. > typedef enum {0, 1, 2, 3} four_val > four_val x; > > x = (four_val) some_int; > .... > assert( x < 4); > > The compiler will drop in a check at the cast to ensure that the wrong > value is not getting stored into x. Then, it will proceed to eliminate > the check that x < 4, because it knows that 0..3 are the only legal > values of x. However, if there is a hardware bug, the value of x will > get changed between the definition point and the use point. Well actualy: since 4 is not a valid value for the enum four_val the Ada compiler won't compile the code - Ada does not automaticy convert enums into integer. The way you would do it in Ada is pragma Assert (x'Valid); The 'Valid attribute checks if a variable contains a valid value. >When bringing up hardware, I like to have a little more control over >where the run-time checks are going to be placed. This is another niche >situtation in which the compiler's "automatic" checking does the wrong >thing. 'Valid is used when a variable may contain an invalid value because of calling a non Ada function or maybe a hardware problem :-) . You may also use "pragma Volatile" if you fear that a variable chances its value. Which is the very same in C89: without "volatile" the optimizer may remove a access to a variable. No difference between C and Ada once optimizer kicks in. But then: most C programmers fear the optimizer while most Ada programmers welcome the optimizer. With Regards Martin -- mailto://krischik@users.sourceforge.net Ada programming at: http://ada.krischik.com