Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!brunix!sdm
From: sdm@cs.brown.edu (Scott Meyers)
Newsgroups: comp.lang.c++
Subject: Re: Nonvirtual base classes in MI
Message-ID: <63176@brunix.UUCP>
Date: 31 Jan 91 20:14:36 GMT
References: <1159@zinn.MV.COM>
Sender: news@brunix.UUCP
Reply-To: sdm@cs.brown.edu (Scott Meyers)
Organization: Brown University Department of Computer Science
Lines: 40

In reponse to my posting, Michael J. Vilot described his uses of nonvirtual
base classe with MI.  His examples were interesting, but I didn't see any
uses of a DAG.  Perhaps I wasn't explicit enough in what I was looking for.
What I want to see is an example that can be boiled down to this:

        A       class A { ... };
       / \
      /   \
     B     C    class B: public (or private) A { ... };
      \   /     class C: public (or private) A { ... };
       \ /
        D       class D: (optionally virtual) public (or private) B, 
                         (optionally virtual) public (or private) C { ... };

What's important here is that neither B nor C inherits from A as a virtual
base.  That results in the memory layout of a D object looking like this,
at least conceptually:

    +------------+
    | B's A Part |
    +------------+
    | B Part     |
    +------------+
    | C's A Part |
    +------------+
    | C Part     |
    +------------+
    | D Part     |
    +------------+

Notice that there are two A parts in a D object.

For the record, I fully agree with Michael's distinction between public and
private inheritance.  I'm especially interested in examples of the above
the use only public inheritance.

Scott

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