Re: [boost] Re: Question about interpretation of ISO C++ standard

From: John Max Skaller (skaller_at_[hidden])
Date: 2001-05-20 04:50:24

rwgk_at_[hidden] wrote:

> Would this be a valid summary:
>   - A fully conforming compiler will find the friend functions
>     through Koenig lookup, and only through Koenig lookup.

        Perhaps I'm missing something, but anyhow ..

The role of 'friend' functions has changed since ARM days.
It used to be you could 'declare' and even define a friend
function inside a class. But then, there was a problem
that to find it from outside the class, it needed to
be 'injected' into the scope outside the class.

This 'friend injection' turned out to cause all sorts
of problems (especially with templates involved as well).
So friend functions _first declared in a class_ are no 
longer injected outside the class.

The solution is: ALWAYS declare the function first,
outside the class. Like this:

        void f();
        class X { friend void f(); };
        void f() { .. }

The friend declaration does nothing here except
let the definition of f get at the private parts of X:
it has no impact on lookup, it is refering to an already
declared function. The function f() is defined after the
class definition to get at the private part of the class.

More simply: do NOT use friend declarations to declare
anything. Just use them to grant friendship.
        
-- 
John (Max) Skaller, mailto:skaller_at_[hidden]
10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
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