Generic getter with C++11

I want to try to do a generic getter by using C++11, but I have an issue if I try to define the generic getter outside the template class.

This code works fine

template <typename T>
class test
{
  public:
    ........
    //generic getter
    template <typename F>
    auto getter_elem_member(F fun)->decltype(fun())
    { return elem.fun(); }
  private
    T elem;                             
};

but if I try the code in this way:

template <typename T>
class test
{
  public:
    ........
    //generic getter
    template <typename F>
    auto getter_elem_member(F fun)->decltype(fun());
  private
    T elem;                             
};

template <typename T>
template <typename F>
auto test<T>::getter_elem_member(F fun)->decltype(fun())
{ return elem.fun(); }

I obtain the error "Member declaration not found". Where am I wrong?

Thanks in advance for any suggestions