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: 103376,1e0472f55fc12a52 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2003-02-19 05:28:55 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!skynet.be!skynet.be!fu-berlin.de!uni-berlin.de!tar-alcarin.cbb-automation.DE!not-for-mail From: Dmitry A. Kazakov Newsgroups: comp.lang.ada Subject: Re: How do I create an object instance from a tag? Date: Wed, 19 Feb 2003 14:26:36 +0100 Message-ID: References: NNTP-Posting-Host: tar-alcarin.cbb-automation.de (212.79.194.111) Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: fu-berlin.de 1045661196 49722461 212.79.194.111 (16 [77047]) X-Newsreader: Forte Agent 1.8/32.548 Xref: archiver1.google.com comp.lang.ada:34226 Date: 2003-02-19T14:26:36+01:00 List-Id: On Wed, 19 Feb 2003 10:39:56 +0100 (MET), "Grein, Christoph" wrote: >Problem with this proposal is abstract types. There must not be objects of an >abstract type. > >So if myTag denotes an abstract type, the proposal is illegal. It should at >least propagate Program_Error. Constraint_Error, I would say. It is statically uncheckable. BTW, the source of the problem with it is that S'Tag "leaks". IMO there is no much sense in having tags of imaginary objects. So S'Tag could raise an exception if S is abstract (or unconstrained?). >So there are good reasons why there is not yet a solution for this problem. Similar problem exists with S'Class'Input, if you mangle stream data so that an abstract type tag appears there. >(A solution, together with some trivial other amendments, could be used to find >the nearest common ancestor of two tagged objects. Currently there is no way to >find it.) I do not see it as the same problem. Are there many cases where the above could be useful? Sort of MD for poor? (:-)) Tag comparisons (>, >=, <, <=) could be indeed useful. --- Regards, Dmitry Kazakov www.dmitry-kazakov.de