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From: howell@bert.llnl.gov (Louis Howell)
Newsgroups: comp.std.c++
Subject: Re: Declarations of Member Functions Outside Class Definitions
Message-ID: <65800@lll-winken.LLNL.GOV>
Date: 3 Aug 90 00:37:13 GMT
References: <46393@brunix.UUCP> <65729@lll-winken.LLNL.GOV> <1946@ux.acs.umn.edu>
Sender: usenet@lll-winken.LLNL.GOV
Reply-To: howell@bert.llnl.gov (Louis Howell)
Organization: Lawrence Livermore National Laboratory
Lines: 56

In article <1946@ux.acs.umn.edu>, hopper@ux.acs.umn.edu (hopper) writes:
|>In article <65729@lll-winken.LLNL.GOV> howell@bert.llnl.gov (Louis
Howell) writes:
|>>In article <46393@brunix.UUCP>, sdm@cs.brown.edu (Scott Meyers) writes:
|>>|>Proposed:
|>>|>
|>>|>  That it be possible to declare member functions outside of class
|>>|>  declarations exclusively for the purpose of later friend declarations.
|>>|>
|>>|>Example:
|>>|>
|>>|>  class Example;                      // currently legal
|>>|>  void Example::f(int);               // currently illegal, but
would be ok
|>>|>
|>>|>  class Sample {
|>>|>    friend void Example::f(int);      // currently legal, provided class
|>>|>                                      // Example has been defined
|>>|> <stuff deleted here>
|>>|>  };
|>>
|>>Why should even this be necessary?  The friend declaration contains all
|>>of the information necessary to deduce the declarations of Example and
|>>Example::f(int), so why not omit these declarations too?
|>
|>Stuff deleted.
|>
|>	I'm not precisely certain of how this is implemented, but what if
|>you declared a virtual member function of a class, and then use the
|>mechanism proposed in this article to declare it to be a friend? If you
|>called this function, how would the compiler generate the code to select the
|>proper virtual function if it was unaware of the other parts of the class
|>declaration?

More stuff deleted.

I'm not sure that I understand what your objection has to do with the idea
of friends.  I'm not proposing any change to the virtual function mechanism
or the required order of declarations.  As I understand it, at least, all a
friend declaration accomplishes is an override to the privacy rules.  I want
to be able to tell the compiler to remember an exception of the following form:

"The private data (and functions) of this class should be accessible to a
function called f(int) in a class called Example."

It shouldn't matter if the compiler has ever heard of Example or
Example::f(int), all it has to do is remember that a function with that
name should have access to private parts of class Sample.  If the function
is virtual, then a separate friend declaration would be required for the
functions Derived_from_Example::f(int), Also_Derived_from_Example::f(int),
and so on, if they are also to have special access.                     
Am I missing something here, or are we talking about two different things?

Louis Howell

#include <std.disclaimer>