Path: utzoo!attcan!ncrcan!becker!pantor!richard
From: richard@pantor.UUCP (Richard Sargent)
Newsgroups: comp.lang.c++
Subject: Derived can't access protected members of base's
Message-ID: <56.UUL1.3#5109@pantor.UUCP>
Date: 16 Mar 90 21:55:32 GMT
Organization: Pansophic Systems Inc, Graphics Product Company
Lines: 34

We just got bitten by a 2.0 "gotcha". I wonder if anyone "in the know"
can explain the reasons for the restriction, and whether there is
some one who can provide an explanation for doing what we are trying
to do.

C++ 2.0 very clearly states (acc.to Lippman) that "The derived class
has no special access privilege to objects of its base class. Rather,
the derived class has access privilege to the nonprivate inherited
members of a derived class object." (See Lippman, page 314 and 316)

This either was not the case in 1.2, or the compiler was more lax
in regard to this rule.

The way we see the situation, we have to disagree with the restriction.
However, I am not foolish enough to think that BS does not have good
reasons for doing so. I sure would like to understand, 'though.

To our mind, we have a class derivation tree (root class and a number
of derived branches). We think that any object of a type from that
tree of classes should be able to access the protected members of
other objects also of that tree, but no class not in the tree.

Assume we have an array of objects from that tree (or pointers to,
it makes no real difference). We wish to traverse the array and
access a protected member from each object (for whatever reason).
It seems we should be able to use a "base*" pointer, and just
access the item. So how can we accomplish this?

Making the member public makes it too public :-).

Any and all suggestions appreciated. Thanks.

Richard Sargent                   Internet: richard@pantor.UUCP
Systems Analyst                   UUCP:     ...!mnetor!becker!pantor!richard