Path: utzoo!attcan!uunet!dino!ux1.cso.uiuc.edu!brutus.cs.uiuc.edu!psuvax1!psuvm!uh2
From: UH2@psuvm.psu.edu (Lee Sailer)
Newsgroups: comp.object
Subject: Re: Views in OO languages
Message-ID: <90039.113649UH2@PSUVM.BITNET>
Date: 8 Feb 90 16:36:49 GMT
References: <1385@tnoibbc.UUCP>
Organization: Penn State University
Lines: 20

In article <1385@tnoibbc.UUCP>, werner@tnoibbc.UUCP (Werner de Bruijn) says:
>
>Does anyone know how a view on a class can be implemented? The idea comes
>from database environments where instances of a class can be derived from
>instances of other classes.

Right off, I can think of two ways, assuming that I understand what you mean
by "views."  The simple case is where there is an object, say anEmployee,
and you want some users to only have access to certain of anEmployees
attributes and methods.  Just create a subclass of anEmployee, say
aRestrictedEmployee.  Use stubs to hide those methods that need to
be hidden, recode those methods that need more or less security,
create new PrintAs or DisplayAs methods, and so on.

In the database world, views are often complicated joins of many types
of thing.  In this case, systems with multiple inheritance would work
better than those with single.  Of course, the usual tricks for
simulating multiple inheritance like behavio should still work.

                                                               lee