NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/10396

Text File | 1996-08-05 | 1.7 KB | 45 lines

Newsgroups: comp.lang.c++
Path: nntp.coast.net!torn!news!apollo!saed
From: [e-mail] (Saed Aryan,13325,1100,g)
Subject: [Q] how declare a Template class as a friend
X-Nntp-Posting-Host: apollo.engn.uwindsor.ca
Message-ID: <[e-mail]>
Keywords: template, friend
Sender: [e-mail] (Usenet)
Reply-To: [e-mail]
Organization: VLSI Research Group - University of Windsor
Date: Thu, 7 Mar 1996 22:51:36 GMT

Hi all,

--- How do you declare a template class to be a friend of
    another non-template class?

template <class T> class A {};    // the template class A<T's>
class B { friend class A };    // won't do it, A is not a class
template <class V> class B { friend class A<V> };    // B<V's> are not wanted

The point is to declare all classes A<whatever> to be friends of class B.
My aim is to let all classes A<whatever> access private member data of class B,
while B may not be a parent of all classes A<whatever>.

Of course I can go about this by declaring a function f() to be a friend of B,
and have the methods of A<whatever> access B's private member data through f().
But I don't consider this good encapsulation, since any client may use f().

As a remedy to the bad encapsulation, one could also declare a method of A,
say g(), to be a friend of B. But consequently one would ask how to declare all
methods A<whatever>::g() to be friends of B. Friendship is namely declared
inside B, not in the A's.

If a parent class P of all the A<whatever> classes were to be a friend of B,
then regretfully the kids, the derived classes A<whatever>, would not inherit the
friendship. Sigh.

Any suggestions?

Thanks in advance, and please send a copy of your posting to my e-mail as well.
Aryan.             [e-mail]