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: a07f3367d7,fd189a20f95495f3 X-Google-Attributes: gida07f3367d7,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news3.google.com!proxad.net!feeder1-2.proxad.net!news.in2p3.fr!in2p3.fr!news.ecp.fr!news.jacob-sparre.dk!pnx.dk!jacob-sparre.dk!ada-dk.org!.POSTED!not-for-mail From: "Randy Brukardt" Newsgroups: comp.lang.ada Subject: Re: Task components, the rationale Date: Fri, 22 Jul 2011 18:28:16 -0500 Organization: Jacob Sparre Andersen Research & Innovation Message-ID: References: <4e1eae6c$0$6570$9b4e6d93@newsspool3.arcor-online.net> NNTP-Posting-Host: static-69-95-181-76.mad.choiceone.net X-Trace: munin.nbi.dk 1311377298 22879 69.95.181.76 (22 Jul 2011 23:28:18 GMT) X-Complaints-To: news@jacob-sparre.dk NNTP-Posting-Date: Fri, 22 Jul 2011 23:28:18 +0000 (UTC) X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 6.00.2900.5931 X-RFC2646: Format=Flowed; Original X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6109 Xref: g2news2.google.com comp.lang.ada:21271 Date: 2011-07-22T18:28:16-05:00 List-Id: "Maciej Sobczak" wrote in message news:a30f4a5d-baee-40b5-b30d-2a15042868e7@r9g2000yql.googlegroups.com... ... >If you ask me from the top of my head how *exactly* this can be >solved, I will not attempt to give a full solution (hey, the committee >has a full decade for it ;-) ), Well, actually, work on Ada 2020 would need to be finished by late 2018 in order to have a good chance of being standardized in 2020. Since it is mid-2011 now, I think that is more like 7 years than 10. ... > but one of the possible ideas might >involve adding a lifetime information to the access discriminant, just >as it is done for tracking scopes of types and objects with anonymous >access parameters today. That was suggested for Ada 2012 [by me and others], and it turns out that it cannot be done (at least with the sorts of lifetime indications that Ada has used to date). If it was mandated, it would necessarily make Ada implementations far more expensive than they currently are -- so I doubt very much that we'll see that. (Sorry, I don't remember which AI we were discussing at the time, so I can't give you a reference.) The static accessibility model for access discriminants is *very* problematical; it leads to distributed overhead for functions that might return something with a discriminant -- yet that still is considered preferable to any dynamic model. My preference is to not use them at all (not always possible, as shown by some of these examples). Randy. Randy.