[c++0x] _Tuple_impl and typename reference_wrapper<T>::type&&

[Pedro Lamarão]

I traced my difficulty with the <tuple> in HEAD to the following case:

[psilva@desen cxx]$ cat MoveOnly.hpp
#ifndef MOVEONLY_HPP
#define MOVEONLY_HPP

struct MoveOnly {

        MoveOnly () { }

        MoveOnly (MoveOnly&&) { }

        MoveOnly& operator= (MoveOnly&&) { return *this; }

private:
        MoveOnly (MoveOnly const&); // = delete
        MoveOnly& operator= (MoveOnly const&); // = delete
};

inline
MoveOnly
make_move_only () { return MoveOnly(); }

#endif

[psilva@desen cxx]$ cat test.cpp
#include <utility>

#include "MoveOnly.hpp"

class A {
public:

        template <typename T>
        explicit
        A (typename std::remove_reference<T>::type&&) { }

};

int
main (int argc, char* argv[]) {

        A a(make_move_only());

}

[psilva@desen cxx]$ g++-4.3 --std=c++0x test.cpp
test.cpp: In function 'int main(int, char**)':
test.cpp:17: error: no matching function for call to 'A::A(MoveOnly)'
test.cpp:5: note: candidates are: A::A(const A&)


I don't actually know what to think about the test above.

This is exactly what happens in _Tuple_impl when passed an rvalue: the
equivalent template constructor overload never enters the overload
set.

This doesn't seem to be a substitution failure.

Is this code valid?

-- 
 Pedro Lamarão

 "The True Self is the meaning of the True Will:
   know thyself through Thy Way."
                                        -- The Book of Thoth