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=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fac41,9a0ff0bffdf63657 X-Google-Attributes: gidfac41,public X-Google-Thread: 103376,4b06f8f15f01a568 X-Google-Attributes: gid103376,public X-Google-Thread: f43e6,9a0ff0bffdf63657 X-Google-Attributes: gidf43e6,public X-Google-Thread: 1108a1,9a0ff0bffdf63657 X-Google-Attributes: gid1108a1,public From: Mike Spille Subject: Re: Software landmines (loops) Date: 1998/09/01 Message-ID: <35EC1590.D50DB8F6@tisny.com>#1/1 X-Deja-AN: 386897040 Content-Transfer-Encoding: 7bit References: <902934874.2099.0.nnrp-10.c246a717@news.demon.co.uk> <6r1glm$bvh$1@nnrp1.dejanews.com> <6r9f8h$jtm$1@nnrp1.dejanews.com> <6renh8$ga7$1@nnrp1.dejanews.com> <6rf59b$2ud$1@nnrp1.dejanews.com> <6rfra4$rul$1@nnrp1.dejanews.com> <35DBDD24.D003404D@calfp.co.uk> <6sbuod$fra$1@hirame.wwa.com> <35f51e53.48044143@ <904556531.666222@miso.it.uq.edu.au> <35EAEC47.164424A7@s054.aone.net.au> <35EBBFAF.DE38C061@s054.aone.net.au> Organization: Transaction Information Systems Content-Type: text/plain; charset=us-ascii MIME-Version: 1.0 Newsgroups: comp.lang.eiffel,comp.object,comp.software-eng,comp.lang.ada Date: 1998-09-01T00:00:00+00:00 List-Id: James Weirich wrote: > > Matthew> Let's once again compare the decision tables. If we > Matthew> re-write the code, to put it into Matt-like (because Matt > Matthew> likes it) syntax: > > Matthew> equal (l,r: LIST): BOOLEAN is > Matthew> require > Matthew> l /= Void and r /= Void > Matthew> do > Matthew> if l.count /= r.count then > Matthew> return False > Matthew> end > Matthew> from > Matthew> l.start; r.start > Matthew> until > Matthew> l.off > Matthew> loop > Matthew> if l.item /= r.item then > Matthew> return False > Matthew> end > Matthew> l.forth; r.forth > Matthew> end > Matthew> return True > Matthew> end > > Matthew> This version has only two rules in the decision table for > Matthew> the loop predicate: > > Matthew> 1 2 > Matthew> l.off T F > > Yes, but you are ignoring the fact that there are now two loop exits. > If you ask the question "When will the loop terminate?", you must > consider all the exits, including the early return. > Would your average programmer ask the question "Where will the loop terminate?", or "What does the function do?". I think the latter question is alot more important. I personally subscribe to the technique of "bailing-out" as soon as possible in a function. This has two effects: nesting later on is greatly reduced (I find if-else nesting affects readability), and the early-bailouts give me guarantees later in the code that I don't need to check for. > So instead of a single, 2 entry table, you have two 2-entry tables. > Combining them into a single table will produce the same 4 entry table > as the one you produced for Loryn Jenkins's code. > > Seems to me the complexity is about equivalent. > > -- > -- Jim Weirich jweirich@one.net http://w3.one.net/~jweirich > --------------------------------------------------------------------- > -- "A distributed system is one in which I cannot get something done > -- because a machine I've never heard of is down." --Leslie Lamport -Mike