Polymorphic constructors

Writing polymorphic constructors(such as make_tuple) is a boilerplate that has to be written over and over again for template classes:

template <class T>
struct unwrap_refwrapper
{
    typedef T type;
};
 
template <class T>
struct unwrap_refwrapper<std::reference_wrapper<T>>
{
    typedef T& type;
};
 
template <class T>
struct unwrap_ref_decay
: unwrap_refwrapper<typename std::decay<T>::type>
{};

template <class... Types>
std::tuple<typename unwrap_ref_decay<Types>::type...> make_tuple(Types&&... args)
{
    return std::tuple<typename unwrap_ref_decay<Types>::type...>(std::forward<Types>(args)...);
}

The construct function takes care of all this boilerplate, and the above can be simply written like this:

BOOST_HOF_STATIC_FUNCTION(make_tuple) = construct<std::tuple>();