Hi,
Today I noticed the new -ffriend-injection behavior of g++ 4.1.x, which
I do not really understand:
Consider the following code and command line session:
// File t.cc
1: class C {
2: public:
3: friend C& f (C& x) { return x; }
4: };
5: int main () {
6: C c;
7: f( c ); // okay, found by adnl
8: C & (*ptr) (C&) = f; // error
9: }
***
lohmann@faui48b:~$ g++ --version
g++ (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
Copyright (C) 2006 Free Software Foundation, Inc.
lohmann@faui48b:~$ g++ -o t t.cc
t.cc: In function ‘int main()’:
t.cc:8: error: ‘f’ was not declared in this scope
lohmann@faui48b:~$ g++-3.3 -o t t.cc
lohmann@faui48b:~$ g++ -ffriend-injection -o t t.cc
lohmann@faui48b:~$
The g++ man page states:
*>>>>>
-ffriend-injection
Inject friend functions into the enclosing namespace, so that they are
visible outside the scope of the class in which they are declared.
Friend functions were documented to work this way in the old Annotated
C++ Reference Manual, and versions of G++ before 4.1 always worked that
way. However, in ISO C++ a friend function which is not declared in an
enclosing scope can only be found using argument dependent lookup. This
option causes friends to be injected as they were in earlier releases.
This option is for compatibility, and may be removed in a future release
of G++.
*<<<<<
1) Where can I find this in the standard? From how I understand
ISO/IEC 14882:2003 (Second Edition), sec 11.4 "Friend", sentence 5 it
should exactly work like the "old behavior". Is my 2003 edition of the
standard already outdated?
2) Is it intentional that this practically removes the ability of
passing this functions to a function pointer, as in this case I do not
have an actual argument and therefore argument-dependent-name-lookup
(adnl) does not apply? (In principle, the compiler would be able to know
from the l-value expression where to find "f".)
Thanks a lot!
Daniel
