Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!brutus.cs.uiuc.edu!zweig
From: zweig@brutus.cs.uiuc.edu (Johnny Zweig)
Newsgroups: comp.lang.c++
Subject: Re: When polymorphic, when not?
Message-ID: <1989Dec7.205354.1549@brutus.cs.uiuc.edu>
Date: 7 Dec 89 20:53:54 GMT
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Organization: U of Illinois, CS Dept., Systems Research Group
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I think C-front's behavior in this case is wrong.  The function val() takes
an actual B as an argument (not a pointer to a thing of type B) --  so it
ought to get a memberwise copy of the B members of its argument, and should
not have the subclass-of-B virtual function pointer (consider the case in
which the subclass virtual function manipulates members that are not even
members of a B; those didn't even get passed in to val()!).

It seems the rule ought to be "if it takes a Foo, it takes a real-live
Foo (including doing the Foo version of virtual functions.  If it takes
a pointer/reference to a Foo, it will be able to find all the stuff it
needs to do the Polymorphic Thang."

Of course, since Cfront is the specification of the language, this might
be an incorrect argument.

-Johnny