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From: pal@xanadu.wpd.sgi.com (Anil Pal)
Newsgroups: comp.lang.c++
Subject: Re: friend operator +(l,r) vs. operator +(r)
Message-ID: <1990Nov26.210244.21500@relay.wpd.sgi.com>
Date: 26 Nov 90 21:02:44 GMT
References: <11759@hubcap.clemson.edu>
Sender: news@relay.wpd.sgi.com ( CNews Account )
Reply-To: pal@sgi.com
Organization: Silicon Graphics, Inc.
Lines: 25

In article <11759@hubcap.clemson.edu>, grimlok@hubcap.clemson.edu (Mike Percy) writes:
|>  
|> What semantic/operational and/or stylistic differences are there
|> between these two definitions?
|>  
|> class foo {
|> public:
|>    foo& operator +(foo& rhs);
[... and ...]
|>   friend foo& operator +(foo& lhs, foo&rhs);
|> }

1. The friend operator can perform implicit type conversions on its
first argument.  Thus if you have a foo(int) constructor, then with the
friend operator you can do things like (3 + foovar), where with the
member function operator you would have to have (foovar + 3) to get
your operator.

2. On the other hand, the member function could be made virtual where
the friend function cannot.  In a binary operation like +, however, you
need to dispatch on both argument types in any case.

-- 
Anil A. Pal,	Silicon Graphics, Inc.
pal@sgi.com	(415)-335-7279