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Date: Fri, 06 Nov 2009 03:51:00 -0000
Subject: [Bug c++/41960]  New: g++: friend introduce name into class, violate standard
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From: "pi3orama at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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below code cannot be compiled:

-----------
#define TYPE    N::C
#define ASSIGN  do {} while(0)
//#define ASSIGN        do { x->i = 0;} while(0)
//#define TYPE  N::B
namespace N {
        class B;
        class C;
}
void func(TYPE * x);
namespace N {
        class B { int i; };
        class C {
                int i;
                friend void func(TYPE * x);
        };
}
void func(TYPE * x) { ASSIGN; }
int main()
{
        TYPE x;
        func(&x);
        return 0;
}
-----------

g++ report:

------------
/test-cpp.cpp: In function 'int main()':
./test-cpp.cpp:22: error: call of overloaded 'func(N::C*)' is ambiguous
./test-cpp.cpp:18: note: candidates are: void func(N::C*)
./test-cpp.cpp:15: note:                 void N::func(N::C*)
------------

change

#define TYPE  N::C

to 

#define TYPE    N::B

then the code can be compiled.

According to [namespace.memdef] and [basic.scope.pdecl]:

---------------
friend declarations refer to functions or classes that are members of the
nearest enclosing namespace, but they do not introduce new names into that
namespace (7.3.1.2).
---------------

According to standard, ::func(N::C * x) shouldn't become friend of N::C, but
there should no ambiguous, because 'friend void func(TYPE * x);' look for
N::func(N::C *), and it doesn't exist at all. According to [namespace.memdef],
the names introduced by 'friend' is invisible until its real declaration.

It seems that, g++ wrongly introduces a name: N::func(N::C*) into namespace N,
and when calling func(N::C*), it follows koenig lookup and finds
N::func(N::C*). In the situation of 'friend void N::func(N::B*)', g++ works
correctly.


-- 
           Summary: g++: friend introduce name into class, violate standard
           Product: gcc
           Version: 4.3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pi3orama at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41960