I was working on a SFINAE programme to remove function template instances from the programme if the parameter class or template class is not a base of the collection (see How to get a SFINAE expression to work with template and non-template classes?):

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Classes to test on
class A{};
template <typename T> class B{};
template <typename T0, typename T1> class BB{};
class C{};
template <typename T> class D{};
template <typename T0, typename T1> class DD{};

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Collection of valid types
template <
    template <typename...> class TT
    , typename...Ts>
class collection 
    : A                                        // class A
    , B<get_item<0,Ts...>>                     // class B<X>
    , BB<get_item<0,Ts...>, get_item<1,Ts...>> // class BB<Y, Z>
{};

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Function to enable on
template <typename T>
enable_if_is_base_of<T, collection> test(T&&)
{    return enable_if_is_base_of<T, collection>();
}

Now I was wondering if the specifications of B<X> or BB<Y,Z> where they are defined as being base of collection can somehow become inverted from BB<get_item<0,Ts...>, get_item<1,Ts...>> to template_with_params<BB, ...Ts>, or even template_with_params<BB, 2, ...Ts>. Possible?