http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344
Bug #: 50344
Summary: friend declaration confused by const qualifier
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: r...@gcc.gnu.org
CC: ja...@gcc.gnu.org
template <typename T> class C
{
friend T;
int i;
};
struct S
{
int f()
{
C<const S> c;
return c.i;
}
};
This is valid C++11, but fails with:
ac.cc: In member function 'int S::f()':
ac.cc:4:8: error: 'int C<const S>::i' is private
ac.cc:12:17: error: within this context
The problem is that the friend declaration names "const S" so S is not
considered a friend, it works if C<S> is used. The standard says "If the type
specifier in a friend declaration designates a (possibly cv-qualified) class
type, that class
is declared as a friend"
This bug predates the implementation of the C++0x extended friend rules, as
shown by this example using a non-standard friend declaration supported by G++:
template<typename T> struct identity { typedef T type; };
template <typename T> class C
{
friend class identity<T>::type;
int i;
};
struct S
{
int f()
{
C<const S> c;
return c.i;
}
};
This works with all versions of G++ is C<S> is used, but not C<const S>
