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-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,a1ce307c10055549 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2002-12-21 07:54:44 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!newsfeed.cwix.com!news.binc.net!kilgallen From: Kilgallen@SpamCop.net (Larry Kilgallen) Newsgroups: comp.lang.ada Subject: Re: calenday (was Re: IBM Acquires Rational Ada Date: 21 Dec 2002 08:54:42 -0600 Organization: LJK Software Message-ID: References: <5JfM9.395655$P31.145145@rwcrnsc53> NNTP-Posting-Host: eisner.encompasserve.org X-Trace: grandcanyon.binc.net 1040485981 15119 192.135.80.34 (21 Dec 2002 15:53:01 GMT) X-Complaints-To: abuse@binc.net NNTP-Posting-Date: Sat, 21 Dec 2002 15:53:01 +0000 (UTC) Xref: archiver1.google.com comp.lang.ada:32160 Date: 2002-12-21T08:54:42-06:00 List-Id: In article , "Marin David Condic" writes: > Fine. Same deal with messages or other structures. Place them after the tag > (exactly represented) and load/store with an offset from the start of the > record. I suppose it might be a bit easier if the tag appears after > everything - but that just creates problems if you want to extend the > record. I can always do overlays or offsets or addresses or something > similar to get past the tag so long as I know exactly where it is and how > big it is. > > Would you think the case you cited would be something that would need tagged > records or would it more appropriately be represented by a plain-vanilla > record? Where would you want to put the tag if not at offset 0? > > MDC > -- > ====================================================================== > Marin David Condic > I work for: http://www.belcan.com/ > My project is: http://www.jast.mil/ > > Send Replies To: m c o n d i c @ a c m . o r g > > "I'd trade it all for just a little more" > -- Charles Montgomery Burns, [4F10] > ====================================================================== > > Larry Kilgallen wrote in message > news:FxwVAF3i62TM@eisner.encompasserve.org... >> >> It depends on whether there are external constraints on the record. >> VMS kernel data structures, for instance, use the first 64 bits for >> a doubly-linked list, the next 16 bits for length and the 16 bits >> after that for a "type" (the closest thing to a constraint or tag). >> >> Interoperation with other languages is crucial in this domain, unlike >> all-Ada environments. The allocation of these structures must start at the queue link longwords, since they get allocated and deallocated by non-Ada components. I have dealt with this in Ada93 for ordinary variant records, but it seems to me that tags have the same issue as discriminants. The start of the record is _not_ ok. Randy's answer about leaving a hole seems the best I have read so far.