Proposed resolution:

Change [forward]:

template <class T> struct identity
{
    typedef T type;
    const T& operator()(const T& x) const;
};

const T& operator()(const T& x) const;

Returns: x.

N1856 defines struct identity in <utility> which clashes with the traditional definition of struct identity in <functional> (not standard, but a common extension from old STL). Be nice if we could avoid this name clash for backward compatibility.