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 X-Google-Thread: a07f3367d7,dbbbb21ed7f581b X-Google-Attributes: gida07f3367d7,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news1.google.com!news3.google.com!feeder.news-service.com!feeder.erje.net!newsfeed.velia.net!noris.net!newsfeed.arcor.de!newsspool2.arcor-online.net!news.arcor.de.POSTED!not-for-mail From: "Dmitry A. Kazakov" Subject: Re: Operation can be dispatching in only one type Newsgroups: comp.lang.ada User-Agent: 40tude_Dialog/2.0.15.1 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Reply-To: mailbox@dmitry-kazakov.de Organization: cbb software GmbH References: <025105f2-5571-400e-a66f-ef1c3dc9ef32@g27g2000yqn.googlegroups.com> <94e76749-c49c-45aa-b7dc-386da0d71c66@e4g2000prn.googlegroups.com> <1u0im1tdws15u.1n9v9rz7bu4t4$.dlg@40tude.net> <39kf90ha60px$.d7746cf5cx6h.dlg@40tude.net> <691d6892-bc5e-4d81-8025-c36556bf2593@13g2000prl.googlegroups.com> <1h9hilcg5i6il.12edpgu4szw1h.dlg@40tude.net> <1wtsriaxu0s4s$.ikwnnz5teukp$.dlg@40tude.net> <1iipp3bn16fe2.yqa1gz1ru17a$.dlg@40tude.net> Date: Fri, 20 Nov 2009 09:34:51 +0100 Message-ID: <18wh86jvjvoe0.cofxcc8udm6q$.dlg@40tude.net> NNTP-Posting-Date: 20 Nov 2009 09:34:49 CET NNTP-Posting-Host: bf34813e.newsspool3.arcor-online.net X-Trace: DXC=WId\m58:K]L6PJ?[X6JIXEMcF=Q^Z^V3H4Fo<]lROoRA8kFO;HKV>EVbJBL X-Complaints-To: usenet-abuse@arcor.de Xref: g2news1.google.com comp.lang.ada:8162 Date: 2009-11-20T09:34:49+01:00 List-Id: On Thu, 19 Nov 2009 17:54:40 -0600, Randy Brukardt wrote: > "Dmitry A. Kazakov" wrote in message > news:1iipp3bn16fe2.yqa1gz1ru17a$.dlg@40tude.net... >> On Wed, 18 Nov 2009 18:27:42 -0600, Randy Brukardt wrote: >> >>> "Dmitry A. Kazakov" wrote in message >>> news:1wtsriaxu0s4s$.ikwnnz5teukp$.dlg@40tude.net... >>> ... >>>>> OK, I don't understand this. First, I don't understand what about >>>>> accessibility checks was a disaster; >>>> >>>> Because they are the major contributor to hours spent on debugging >>>> unhandled exceptions. >>> >>> That seems odd to me. I rather *like* getting unhandled exceptions, because >>> it is almost always easy to see what the problem is from the exception name >>> and the traceback. >> >> Only theoretically. Practically, the existing handlers of "legal" >> exceptions get perplexed, the stack gets wound up causing a cascade of >> exceptions in Finalize's. > > That might be true in general, but definitely not in this case: a handler > for Program_Error is *always* wrong (unless it is a global handler for *any* > exception), as Program_Error always represents a program bug. So I don't see > how "existing" handlers can be confused. exception when Error : others => some cleanup -- This usually becomes a problem raise; > It is necessary to treat all Adjust and Finalize routines like task bodies > in that they need a "when others" handler -- otherwise the exceptions are > sucked up and you get completely lost. Our programming standard requires > such handlers (generally, they output Exception_Information to the logging > facility - and almost every significant Ada system needs some sort of > logging facility). Yes, but this does not help. Upon exception propagation (Constraint_Error), you get some objects finalized. This in turn causes a snowball of exceptions in finalized objects, because no design is robust to hold any error at any place. In the end you have a huge log of meaningless messages, which only complicate debugging. Sometimes I which Ada had "halt at once" statement which would stop all tasks and hold any I/O. But of course the proper solution would be contracted exceptions. >> The difference is that for string bound there is a way to do it safe and >> for 'Access there is none (and I also agree with Robert's response.) > > Well, Ada 2012 (or whatever it will be called) should help that out by > giving you a way to compare accessibilites (via memberships). So at least > you will be able to make checks to avoid the problem. Better than nothing, > but still not ideal. The better way to avoid the problem is to never, ever > use anonymous access types. (Named access types have checks that are always > made at compile-time for most compilers -- but not Janus/Ada, because of > generic sharing.) The problem is not bound to only anonymous types. It also appears when you convert access types. The source type (or both) might be a formal generic parameter, so you cannot statically ensure that a "local" pointer is converted no a "less local" one. Pool specific pointers need to be converted though one target object is derived from another. Here everything is broken: generic contract, meaningless conversion, meaningless check, meaningless exception. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de