Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!usc!masotti
From: masotti@usc.edu (Glauco Masotti)
Newsgroups: comp.lang.c++
Subject: access to protected members
Message-ID: <MASOTTI.89Jul17110844@lipari.usc.edu>
Date: 17 Jul 89 18:08:44 GMT
Sender: news@usc.edu
Organization: University of Southern California
Lines: 69

I had some problems using protected members. I was pretty confident, after
reading the "evolution paper" from Bjarne, that my files would compile, but I
received instead complains from the compiler.  I am using g++, 1.35.0+, so I
first thought of a bug in the compiler and I wrote to the FSF. I kept
exchanging mail with Doug Lea. He told me I should be right, and that he also
would like protected to work the way I used them, but that this doesn't
conform to AT&T 2.0 specs. The interpretation of the evolution paper seems
therefore to be cumbersome, but he also told me to have discussed the matter
with Bjarne himself, to be sure of his interpretation.
 
The following is the example:

---------------------------------------

#include <stream.h>

struct A {

	A(int i) {j=i;}
	void increment() {j++;}
	print() {cout<<j<<"\n";}

protected:
	int j;
};

struct B : A {

	int k;
	A* a;
	B(int i, int j, A* x) : A(i) {k=j; a=x;}
	print() {cout<<j<<" "<<k<<" "<<a->j"\n";}
};


main()
{
	int i=9;

	A a(i);
	a.increment();
	a.print();

	B b(2, 3, &a);
	b.print();
}

------------------------------------------------

Here a protected member of a class is accessed through a pointer in a member
function of a derived class. 
To me this should be allowed, I find pretty counterintuitive the contrary. 
I would like to know what people think.  If Andrew or Bjarne are listening I
would appreciate very much their response.

In any case if I cannot write something like the previous example, I think the
cases where the protection mechanism will help instead of being a burden will
shrink significantly. Therefore the problems protected was intended to solve (as
reported in the evolution paper) will not be solved and we will be forced to
resort again to public everything or make a lot of friends (which in C++ is
not as good as in life :-)).

-Glauco Masotti

masotti@lipari.usc.edu


P.S. This is my first posting, so... Hello to everybody! You may here from me
again if I keep working on my current project.