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From: jnw@shades.cis.ufl.edu (Joseph N. Wilson)
Newsgroups: comp.lang.eiffel
Subject: Re: Inheritance and Information Hiding
Message-ID: <27010@uflorida.cis.ufl.EDU>
Date: 19 Feb 91 18:38:31 GMT
References: <4810@mindlink.UUCP> <1101@tetrauk.UUCP>
Sender: news@uflorida.cis.ufl.EDU
Reply-To: jnw@shades.cis.ufl.edu (Joseph N. Wilson)
Organization: University of Florida CIS dept.
Lines: 23

I was directed to this discussion (indirectly) by Chris Clifton of Princeton.

In article <1101@tetrauk.UUCP>, simons@tetrauk.UUCP (Simon Shaw) writes:
 [...]
|> 1. Inheritance is about specialisation.
|> 
|> 2. Specialisation is often a _restriction_ of the range of allowed
|> circumstances.
|> 
|> 3. Ergo, not all the features of a parent class can necessarily be
|> implemented on a child object.
|> 
 [...]
|> Simon Shaw ; simons@tetrauk.uucp ; net.lurker

This sort of problem is evident even in languages with no explicit inheritance
mechanism.  Consider integer subranges of Pascal.  Addition of two values
belonging to some subrange a..b does not necessarily yield a value in a..b.
It is not reasonable to assume that all properties of an algebra will hold
for a similar subset algebra inheriting values and operations.

joe wilson
(jnw@cis.ufl.edu)