Path: utzoo!attcan!uunet!mcvax!ukc!reading!cf-cm!cybaswan!eeartym
From: eeartym@cybaswan.UUCP (Dr R.Artym eleceng )
Newsgroups: comp.lang.c++
Subject: Re: Friend specifier considered harmful
Message-ID: <79@cybaswan.UUCP>
Date: 12 Sep 88 02:50:23 GMT
References: <61@cybaswan.UUCP> <1988Sep2.174327.6439@ateng.uucp> <8163@alice.UUCP>
Reply-To: eeartym@cybaswan.UUCP (Dr R.Artym eleceng )
Organization: University College of Swansea
Lines: 35

In article <8163@alice.UUCP> bs@alice.UUCP (Bjarne Stroustrup) writes:

> A friend function can be used to express that coercion is acceptable
> for the left hand operand of an operator. Such coercions are not aceptable
> for the left hand operand of an operator defined as a member function:
>	... program ...
> This could be expressed without the use of friend functions (but not
> in C++, since you cannot specify a member function for a built-in type
> so int::operator(Int) cannot be defined). It could, however, also be
> expressed without the use of member functions.
> It can also be expressed without the use of coercions, but that leads
> to an explosion of operator functions.

I reckon this is the only convincing reason for using the friend specifier
mentioned so far in this discussion.  It is important to note that it stems
from a limitation in C++ as it stands at the moment, and does not imply that
loosening the class scope walls is a good thing.  Furthermore, this kind of
usage is completely benign, really just a syntactic artifice:  the scope
region does not flood out into another class.

This pours some light on the real source of my discomfort --- my original
phrase should perhaps be amended to `Friend classes considered harmful'.
Such sledgehammer usage of the specifier probably indicates a non-OO design
approach or that structural soundness has been sacrificed for efficiency.
(Examples to the contrary still welcome!)
-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Keywords:  Parallel, Applicative, and Object-Oriented Languages and Systems
---------------------------------------------------------------------------
Dr. Richard Artym,              +   UUCP   :  ..!ukc!pyr.swan.ac.uk!eeartym
Electrical Engineering Dept.,   +   JANET  :  eeartym@uk.ac.swan.pyr
University of Wales,            +   Phone  :  [(0792) or (+44 792)]  295536
Swansea, SA2 8PP,               +   Fax    :  [(0792) or (+44 792)]  295532
U.K.                            +   Telex  :  48358
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~