copy qualifiers

template< typename from, typename to >
struct copy_cv_reference
{

    using type = to;

};

template< typename from, typename to >
struct copy_cv_reference< from const, to >
        : copy_cv_reference< from, to const >
{

};

template< typename from, typename to >
struct copy_cv_reference< volatile from, to >
        : copy_cv_reference< from, volatile to >
{

};

template< typename from, typename to >
struct copy_cv_reference< from const, to & >
        : copy_cv_reference< from, to const & >
{

};

template< typename from, typename to >
struct copy_cv_reference< volatile from, to & >
        : copy_cv_reference< from, volatile to & >
{

};

template< typename from, typename to >
struct copy_cv_reference< from const, to && >
        : copy_cv_reference< from, to const && >
{

};

template< typename from, typename to >
struct copy_cv_reference< volatile from, to && >
        : copy_cv_reference< from, volatile to && >
{

};

template< typename from, typename to >
struct copy_cv_reference< from &, to >
        : copy_cv_reference< from, to & >
{

};

template< typename from, typename to >
struct copy_cv_reference< from &&, to >
        : copy_cv_reference< from, to && >
{

};

namespace test
{

struct A {};
struct B {};
static_assert((std::is_same< copy_cv_reference< volatile const A &, B >::type, volatile const B & >{}), "");
static_assert((std::is_same< copy_cv_reference< const A &, B >::type, const B & >{}), "");
static_assert((std::is_same< copy_cv_reference< volatile A &, B >::type, volatile B & >{}), "");
static_assert((std::is_same< copy_cv_reference< A &, B >::type, B & >{}), "");
static_assert((std::is_same< copy_cv_reference< volatile const A &, B >::type, volatile const B & >{}), "");
static_assert((std::is_same< copy_cv_reference< const A &&, B >::type, const B && >{}), "");
static_assert((std::is_same< copy_cv_reference< volatile A &&, B >::type, volatile B && >{}), "");
static_assert((std::is_same< copy_cv_reference< A &&, B >::type, B && >{}), "");
static_assert((std::is_same< copy_cv_reference< volatile const A, B >::type, volatile const B >{}), "");
static_assert((std::is_same< copy_cv_reference< const A, B >::type, const B >{}), "");
static_assert((std::is_same< copy_cv_reference< volatile A, B >::type, volatile B >{}), "");
static_assert((std::is_same< copy_cv_reference< A, B >::type, B >{}), "");

}