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=0.7 required=5.0 tests=BAYES_00,INVALID_MSGID, PDS_OTHER_BAD_TLD 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: 1108a1,9a0ff0bffdf63657 X-Google-Attributes: gid1108a1,public X-Google-Thread: f43e6,9a0ff0bffdf63657 X-Google-Attributes: gidf43e6,public From: dewar@gnat.com Subject: Re: Software landmines (loops) Date: 1998/09/01 Message-ID: <6sfnjt$5br$1@nnrp1.dejanews.com>#1/1 X-Deja-AN: 386659491 References: <902934874.2099.0.nnrp-10.c246a717@news.demon.co.uk> <6r1glm$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> <35EB1706.22E7E52E@draper.com> X-Http-Proxy: 1.0 x11.dejanews.com:80 (Squid/1.1.22) for client 205.232.38.14 Organization: Deja News - The Leader in Internet Discussion X-Article-Creation-Date: Tue Sep 01 02:53:50 1998 GMT Newsgroups: comp.lang.eiffel,comp.object,comp.software-eng,comp.lang.ada X-Http-User-Agent: Mozilla/2.02 (OS/2; I) Date: 1998-09-01T00:00:00+00:00 List-Id: In article <35EB1706.22E7E52E@draper.com>, Tim McDermott wrote: > > > Matthew Heaney wrote: > > > Here's is something I whipped up for another post recently. It's an > > equality operator for a bounded stack. > > > > The implementation of the function has multiple returns. > > > > Does this implementation fit your definition of spaghetti code? > > > > Would the implementation be better by not using multiple returns? > > > > function "=" (L, R : Stack_Type) return Boolean is > > begin > > > > if L.Top /= R.Top then > > return False; > > end if; > > > > for Index in Positive range 1 .. L.Top loop > > if L.Items (Index) /= R.Items (Index) then > > return False; > > end if; > > end loop; > > > > return True; > > > > end "="; > > > > My feeling is that trying to implement this operation using only a > > single return would just make it more complicated. > > How about this: > > function "=" (L, R : Stack_Type) return Boolean is > begin > > Boolean isEqual = True; > Positive Index = 1; > > if L.Top /= R.Top then > isEqual = False; > end if; > > while Index < L.Top && isEqual loop > if L.Items (Index) /= R.Items (Index) then > isEqual = False; > end if; > Index++; > end loop; > > return isEqual; > > end "="; > > What Dykstra was getting at with single entance, single exit is that you can > attempt to reason about the programs that are well structured. In the > second version, you can make assertions about pre- and post-conditions. In > fact they jump out of the loop test. That is not the case with the first > version. > > Tim > > Yes, this is a very predictable response, but I MUCH prefer the original with multiple returns, why? Because when I read return False; I know that is the end of it, and I can immediately verify that this part of the program is correct, and that the value returned in this case is what it should be. I can then forget that case and move to the next one. If on the other hand I read: > isEqual = False; Then I have to keep this in mind, as I read on, to make sure some idiot has not added later on a statement like if some-weird-hard-to-follow-condition then isEqual = True; end if; changing the original value. and of course I have to keep looking, because someone may change the value back to False. Variables are dangerous in themselves, replacing multiple returns by introducing a variable is in this case jumping out of the frying pan into the fire! -----== Posted via Deja News, The Leader in Internet Discussion ==----- http://www.dejanews.com/rg_mkgrp.xp Create Your Own Free Member Forum