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 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Your wish list for Ada 202X Date: Sat, 12 Apr 2014 10:45:54 +0200 Organization: cbb software GmbH Message-ID: <9cm2e094hvj7.sj0t2sh2komn.dlg@40tude.net> References: <7f1c01c5-3563-4b94-9831-152dbbf2ecdc@googlegroups.com> <8bhozh836pyt$.1qctlysud0s2q$.dlg@40tude.net> <1cdsyxjzsfgzm.1synpaujysv21$.dlg@40tude.net> <1aa804jg9qq4o$.wdiq33yo621l.dlg@40tude.net> <1w6eh0aiksmdh$.1h16p7y0b8c6h.dlg@40tude.net> <17twpp4p8u7o$.1idvzaaio4f3t$.dlg@40tude.net> <16388p09ph28u$.1mglp0rm7pli9$.dlg@40tude.net> Reply-To: mailbox@dmitry-kazakov.de NNTP-Posting-Host: AuYlnUSfTZrfhAkRjyySpQ.user.speranza.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: 40tude_Dialog/2.0.15.1 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:19258 Date: 2014-04-12T10:45:54+02:00 List-Id: On Fri, 11 Apr 2014 16:44:13 -0500, Randy Brukardt wrote: > "Dmitry A. Kazakov" wrote in message > news:16388p09ph28u$.1mglp0rm7pli9$.dlg@40tude.net... >> Your example refers to overloading possible for operations on unrelated >> types. I don't see how this is scenario could be possible for a primitive >> MD operation. One of the requirements put on MD is that *all* combinations >> of tags up to the root of the inheritance tree be defined and checked at >> compile time. This requirement automatically precludes appearance of C from >> air. It cannot be primitive and thus the preference rules would not apply >> to it. > > Doesn't matter. First, you'd have to prevent adding or removing new > primitive operations to a hierarchy. That seems like a nasty limitation. What? This limitation is with us since Ada 95! You cannot add a primitive operation after the freezing point in Ada. You cannot remove a primitive operation at all. > Second, you can introduce a new primitive operation by withing ["ripple"] or > using ["Beaujolias"] an existing package that wasn't previously part of the > client. Introducing an otherwise unused package ought not change the > behavior of a client. It will not, because the rule [*] should be that tags higher in the hierarchy (counting from the root) than the highest known tag in the expression should not be considered. E.g. if you have Root <- A <- B <- C Then in the expression A + B, the variant C'(A + B) is automatically depreciated. >> This requirement is actually a problem of MD, I don't know how to solve, >> i.e. how to stretch a hierarchy across several packages. Let two packages >> define two types P and Q and a cross operation F between. When in a third >> package R gets derived from P, then how and where we define F for R and Q, >> provided this third package may know nothing about the package of Q. > > I suppose if you could actually solve such a problem without introducing > crazy usage requirements, you could get the same effect as a preference rule > safely. Possibly. > But I'd guess (and I admit it is a guess) that the problems are > essentially the same and the fact that one clearly fails the test means that > the other would clearly fail the test as well. If so, then OO failed, as you used to say! ---------------- * This rule is akin to no re-dispatch rule -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de