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,c52c30d32b866eae X-Google-Attributes: gidfac41,public X-Google-Thread: 1108a1,c52c30d32b866eae X-Google-Attributes: gid1108a1,public X-Google-Thread: 103376,2ea02452876a15e1 X-Google-Attributes: gid103376,public From: schlegel@informatik.uni-rostock.de (Juergen Schlegelmilch) Subject: Re: Real OO Date: 1996/05/09 Message-ID: #1/1 X-Deja-AN: 153849066 references: organization: Comp Sci Dept, Uni Rostock, Germany reply-to: schlegel@Informatik.Uni-Rostock.de newsgroups: comp.lang.eiffel,comp.lang.ada,comp.object Date: 1996-05-09T00:00:00+00:00 List-Id: On Thu, 9 May 1996 00:52:19 GMT, Don Harrison wrote: > Thanks for the pointer. Have asked cecil@cs.washington.edu for more info. Sorry, I forgot to include numbers in my pointer: The technical report is available as University of Washington CS&E Technical Report 95-08-05 Iowa State University CS Technical Report #95-19 It also says an earlier version appeared in the proceedings of OOPSLA'94. > :the Liskov Substitution Principle, > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > Could you (or somone) explain what this is? Sorry, I'm a bit ignorant. This goes back to an article: Liskov, Barbara. "Data Abstraction and Hierarchy." SIGPLAN Notices 23,5 (May 1988) pg 25. It says that objects of a subclass must not only be structurally substitutable (i.e. show the same interface) but also behaviourally, i.e. they have to accept the same set of event sequences. First of all, this means you cannot have (single-dispatch with) covariance since this allows an object in a subclass to require more specific parameters. Second and more important, the observable changes in the object must be equivalent for all sequences of events (= method calls). --- I have to admid that I never read the original article from Barbara Liskov, so anyone can correct me on the exact definition. Regards, Juergen -- +-----------------------------------------------------------------------------+ Dipl.-Inf. Juergen Schlegelmilch University of Rostock email: schlegel@Informatik.Uni-Rostock.de Computer Science Department http://www.informatik.uni-rostock.de/~schlegel Database Research Group Tel: ++49 381 498 3402 18051 Rostock Fax: ++49 381 498 3404 Germany +-----------------------------------------------------------------------------+