Xref: utzoo comp.lang.eiffel:1329 comp.object:2424
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From: chrisv@runx.oz.au (Chris Velevitch)
Newsgroups: comp.lang.eiffel,comp.object
Subject: Inheritance and Information Hiding
Keywords: oop, ood, Eiffel, inheritance, information hiding
Message-ID: <1991Jan23.224203.3206@runx.oz.au>
Date: 23 Jan 91 22:42:03 GMT
Sender: chrisv@runx.oz.au (Chris Velevitch)
Organization: RUNX Un*x Timeshare.  Sydney, Australia.
Lines: 19

I disagree with allowing a class to access inherited features that are
not exported. It does not make sense that secret features are known to
heir of a class. If a feature is not publicly known, then how can you
know about the feature to use in the descendent class.

Eiffel allows a class to be designed so it has no interface, which can
then be used in descendent classes. What use is a black box in which you
cannot put anything in or take anything out.

When designing a class, a designer makes the interface public, not its
implementation. The user of a class buys services from the class based
solely from its publically known behaviour and features. You can only
inherit features that are known. I consider inheritance as a form of
buying services.

-- 
Chris Velevitch
RUNX Unix Timeshare    | Internet: chrisv@runxtsa.runx.oz.au
Sydney NSW, Australia. |     UUCP: uunet!runxtsa.runx.oz.au!chrisv