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=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fac41,2c6139ce13be9980 X-Google-Attributes: gidfac41,public X-Google-Thread: 1108a1,2c6139ce13be9980 X-Google-Attributes: gid1108a1,public X-Google-Thread: 103376,3d3f20d31be1c33a X-Google-Attributes: gid103376,public X-Google-Thread: f43e6,2c6139ce13be9980 X-Google-Attributes: gidf43e6,public From: donh@syd.csa.com.au (Don Harrison) Subject: Re: Safety-critical development in Ada and Eiffel Date: 1997/08/13 Message-ID: #1/1 X-Deja-AN: 263894092 Sender: news@syd.csa.com.au References: Reply-To: donh@syd.csa.com.au X-Nntp-Posting-Host: dev50 Organization: CSC Australia, Sydney Newsgroups: comp.object,comp.software-eng,comp.lang.ada,comp.lang.eiffel Date: 1997-08-13T00:00:00+00:00 List-Id: Jon S Anthony wrote: :In article donh@syd.csa.com.au (Don Harrison) writes: : :> it can be expected to do a better job of it. If Ada protected types allow :> the designer to explicitly leave objects unlocked (which doesn't appear to :> be supported by the Ada95 Rationale), then they are more permissive but :> in a detrimental way, IMO. : :You're not twigging this stuff. Possibly. :The objects can be unlocked for :_read_ access, but never for any update access. Care to give an example? :> :can requeue requests, :> :> IMO, the situations in which you would use "requeue" are better handled by :> designing differently - perhaps by using an additional class. If anything, :> "requeue" probably encourages poor design. : :Requeue is specifically there to eliminate in principle any timing :errors. The way this works is somewhat subtle, so maybe you are not :twigging this either. On re-reading the Ada95 Rationale, I think I have a handle on this now. (See my response to Ken.) :> simulating the surrounding environment. Then, any assertions :> assuming Ariane 4 inputs would be violated (as would the Ada :> constraint_error). In general, the extra checking afforded by DBC :> would mean more bugs would be identified than if it wasn't :> used. (Yes, I know there is no difference wrt the one that caused :> the failure.) : :The problem with this is the simple observation of "why would the :assertions be there in the first place?" After all, in the particular :case at hand, they were _intentionally_ removed. And with perfectly :sound engineering principles in mind. Assertions in the code _cannot_ :capture the constraints presumed for the context of use. This has to :come from somewhere else (external documentation, "instructions", :"warrenty notes", whatever.) The odd thing here is that this point :should be "blindingly obvious", to use one of your phrases. Yes, I agree it is. I'm talking about (an aspect of) how I think it *ought* to be done, not how it *was* done. Don. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Don Harrison donh@syd.csa.com.au