Newsgroups: comp.lang.eiffel,comp.object,comp.lang.sather,comp.lang.beta Path: news.daimi.aau.dk!news.uni-c.dk!sunic!news.funet.fi!news.eunet.fi!EU.net!howland.reston.ans.net!math.ohio-state.edu!news.acns.nwu.edu!ftpbox!mothost!schbbs!news From: shang@corp.mot.com (David L. Shang) Subject: Re: Cows, Hogs & Farms Reply-To: shang@corp.mot.com Organization: MOTOROLA Date: Fri, 13 Jan 1995 18:11:34 GMT Message-ID: <1995Jan13.181134.15344@schbbs.mot.com> References: <1995Jan12.031516.22136@inca.comlab.ox.ac.uk> Sender: news@schbbs.mot.com (SCHBBS News Account) Nntp-Posting-Host: 129.188.128.126 Lines: 24 Xref: news.daimi.aau.dk comp.lang.eiffel:7177 comp.object:23804 comp.lang.sather:1432 comp.lang.beta:219 In article <1995Jan12.031516.22136@inca.comlab.ox.ac.uk> lady0065@sable.ox.ac.uk (David J Hopwood) writes: > In article <1995Jan9.005627@hobbit>, > Mark S. Hathaway wrote: > >Does Cluster separate the subtyping and inheritance as Sather does? > > No. In Cluster subclassing implies subtyping. IMO this is not a good idea, > because it is useful to be able to use part of the implementation of a class > without subtyping from it. > It is useful to be able to use part of the implementation of a class without subtyping from it when you CANNOT make that subclass be a subtype otherwise safety problem would occur. It is meaningless to use part of the implementation of a class without subtyping from it when you CAN make that subclass be a subtype without safety problem. By Sather, some subclass cannot be subtypes due to covariance. In Cluster, These classes can be subtypes safely. Therefore, Cluster has no need to separate the subtyping and inheritance as Sather does. David Shang