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: fac41,9a0ff0bffdf63657 X-Google-Attributes: gidfac41,public X-Google-Thread: f43e6,9a0ff0bffdf63657 X-Google-Attributes: gidf43e6,public X-Google-Thread: 1108a1,9a0ff0bffdf63657 X-Google-Attributes: gid1108a1,public X-Google-Thread: 103376,4b06f8f15f01a568 X-Google-Attributes: gid103376,public From: Loryn Jenkins Subject: Re: Which wastes more time? (Was Re: Software landmines (loops)) Date: 1998/09/09 Message-ID: <35F56290.AB5491D9@s054.aone.net.au>#1/1 X-Deja-AN: 389083854 Content-Transfer-Encoding: 7bit References: <35F42CAC.6F566DC7@s054.aone.net.au> <35F4F454.542516E4@s054.aone.net.au> X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii X-Trace: news.mel.aone.net.au 905274048 11860 203.12.186.132 (8 Sep 1998 17:00:48 GMT) Organization: TekRite Pty Ltd Mime-Version: 1.0 Reply-To: loryn@acm.org NNTP-Posting-Date: 8 Sep 1998 17:00:48 GMT Newsgroups: comp.lang.eiffel,comp.object,comp.software-eng,comp.lang.ada Date: 1998-09-08T17:00:48+00:00 List-Id: Patrick Doyle wrote: > > In article <35F4F454.542516E4@s054.aone.net.au>, > Loryn Jenkins wrote: > > > >Patrick Doyle wrote: > >> > >> You have a good point that if you commit to the PERSON-CAR_OWNER > >> thing then you've locked yourself out of modelling someone who > >> sells his car. So, it's a design decision. If you're not going > >> to model that, then the extra complexity of the role pattern > >> may not be justified. > > > >Tell me something: How would you envisage PERSON <-- CAR_OWNER working > >together within a program? > > I gave an example earlier of a reporting program which generates > a report based on a moment in time. If a person sells his car, > he will either do so before or after this program is run; > in either case, if he is a CAR_OWNER at the start, he will > be a CAR_OWNER for the duration of the program. That's what I thought. And my response to that is: Why do you need class PERSON at all, in this situation? You're not intending to use it polymorphically with CAR_OWNER. In fact, the only reason for having it is that it existed before, and now you simply want to extend it to cover this CAR_OWNERship situation. Hence, from the point of view of this program, you're modelling a module extension type relationship. Now, can you think of an example application where it would be appropriate to have a sub-type inheritance relationship directly between PERSON and CAR_OWNER? Loryn Jenkins