Befriending a private member function

[Herwig, Björn]

Hello,

I recently came across a rather historic piece of C++ code once written for G++ 3 point
something. It doesn't compile with a G++ 4, as it tries to befriend a private member
function. Okay, this is easily solved by befriending the whole class, but I am really
curious now, why this isn't allowed anymore.

I've read the corresponding sections in "The C++ Programming Language, Special Edition"
and section 11.4 of the C++ 2003 standard, but that still left me clueless.

Could anybody give me a hint?

Best,
Björn A. Herwig

-----
#include <string>

using namespace std;

class A
{
public:
    void pubFunc()
    {
    }

private:
    void privFunc(int)
    {
    }
};

class B
{
public:
    friend void A::privFunc(int);
};

int main(int argc, char** argv)
{
    B b;
    return 0;
}
-----

-----
# g++ --version
g++ (GCC) 3.2.3 20030422 (Gentoo Linux 1.4 3.2.3-r1, propolice)
Copyright (C) 2002 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# g++ -Wall -o test test.cpp
test.cpp: In function `int main(int, char**)':
test.cpp:26: warning: unused variable `B b'
-----

-----
# g++ --version
g++ (Debian 4.3.3-3) 4.3.3
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# g++ -Wall -o test test.cpp
test.cpp:13: error: ‘void A::privFunc(int)’ is private
test.cpp:21: error: within this context
test.cpp: In function ‘int main(int, char**)’:
test.cpp:26: warning: unused variable ‘b’
-----