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 autolearn=ham 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!news4.google.com!news.glorb.com!newsfeed00.sul.t-online.de!t-online.de!newsfeed1.ip.tiscali.net!tiscali!transit1.news.tiscali.nl!dreader2.news.tiscali.nl!not-for-mail Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng Subject: Re: Teaching new tricks to an old dog (C++ -->Ada) 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> <87is4598pm.fsf@insalien.org> <1110054476.533590@athnrd02> <1110059861.560004@athnrd02> <87wtsl7jts.fsf@insalien.org> <1110264816.858853.54020@l41g2000cwc.googlegroups.com> <1110336185.044049.21920@l41g2000cwc.googlegroups.com> From: Ludovic Brenta Date: Wed, 09 Mar 2005 23:29:02 +0100 Message-ID: <87wtsgfo7l.fsf@insalien.org> User-Agent: Gnus/5.1007 (Gnus v5.10.7) Emacs/21.3 (gnu/linux) Cancel-Lock: sha1:GUGJOj5AlotdgmOVouq3tUngNuU= MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Organization: Tiscali bv NNTP-Posting-Date: 09 Mar 2005 23:28:44 CET NNTP-Posting-Host: 83.134.240.205 X-Trace: 1110407324 dreader2.news.tiscali.nl 44105 83.134.240.205:33726 X-Complaints-To: abuse@tiscali.nl Xref: g2news1.google.com comp.lang.ada:8978 comp.lang.c++:44865 comp.realtime:1154 comp.software-eng:4713 Date: 2005-03-09T23:28:44+01:00 List-Id: "Jerry Coffin" writes: > Dr. Adrian Wrigley wrote: > > [ ... ] > >> Isn't there some confusion here? >> >> Surely the "aliasing" issue (ignored by C++ completely(?)) is >> largely independent if the >> "reinterpret_cast"/"Unchecked_Conversion" issue? > > Yes -- he started by mentioning aliasing, but mostly seemed to be > talking about type punning, so that was what I replied to. The > discussion centered around safety, which is essentially orthogonal > to aliasing. No, I did insist on aliasing as the main point, and then briefly about the representation clause that caused two objects to be overlaid. Aliasing is definitely *not* orthogonal to safety. The coding standards I have reviewed for avionics, as well as the "Guide for the use of the Ada programming language in High Integrity Systems" [1] all discuss how aliasing adversely affects safety. It is important, in safty-critical software, to understand aliasing: what it is, when it takes place, and what the consequences are. Performance in this context is a minor concern compared to predictability of the software. [1] http://www.dkuug.dk/JTC1/SC22/WG9/n359.pdf -- Ludovic Brenta.