[Bug c++/54323] New: Friend function declaration not correctly identified with CRTP + enable_if

[vince.rev at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54323

             Bug #: 54323
           Summary: Friend function declaration not correctly identified
                    with CRTP + enable_if
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vince.rev@gmail.com


Created attachment 28051
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28051
.cpp bug example

The following example involving a friend function in a Curiously Recurring
Template Pattern base class with an enable_if default template argument is not
working :

// --------------------------------------------------------------------
#include <type_traits>

// Base class definition
template<template<typename> class CRTP, typename T> class Base
{
    // Friend function declaration
    public:
        template<template<typename> class CRTP0, typename T0, class>
        friend int func(const Base<CRTP0, T0>& rhs);

    // Protected test variable
    protected:
         int n;
};

// Friend function definition
template<template<typename> class CRTP0, typename T0,
class = typename std::enable_if<true>::type>
int func(const Base<CRTP0, T0>& rhs)
{
    return rhs.n;
}

// Derived class definition
template<typename T> class Derived : public Base<Derived, T> {};

// Main
int main()
{
    Derived<int> x;
    func(x);
    return 0;
}
// --------------------------------------------------------------------

g++ (tested with 4.6.1, 4.6.2 and 4.7.1) seems not to be able to match the
definition with the declaration of the function and return the following error
:
"int Base<Derived, int>::n' is protected"