How to pass around parameter packs in C++?

Consider the following example:

template <class T> class method_traits;
template <class T, class Ret, class... Arg> class method_traits<Ret(T::*)(Arg...)> {
public:
    using type = Arg; // this does not work
};

template <class T> using argument_types = typename method_traits<T>::type;

template <class T> class Node {
    T t;
public:
    Node(Input<argument_types<decltype(&T::process)>>... inputs) { // how do I make this work?
        ...
    }
};

The arguments of the constructor of Node<T> depend on the arguments of the method T::process. So if a type T has a method process of the signature float process(float a, int b) the signature of the constructor of Node<T> should look like this: Node(Input<float> a, Input<int> b).

I'm a little bit stuck here. How do I extract the parameter pack from T::process to use it on the constructor of Node?