Deduction guide to extract template template from types

Question

Consider the following class:

// Class definition
template <template <class...> class... Templates>
class template_pack
{
    public:
    template <class... Types>
    constexpr template_pack(const Types&...) noexcept;
};

// Class template argument deduction guide
template <class... Types>
template_pack(const Types&...) -> template_pack</* something here */>

We suppose that the Types... are of the form template <class...> class... Templates. What I would like is:

template_pack pack(std::vector<int>{}, std::list<double>{}, std::deque<char>{});

to lead to:

template_pack<std::vector, std::list, std::deque>;

How to make that work?

Answer 1

I "succeed" with additional traits:

template <typename T> struct template_traits;

// Variadic case
template <template <class...> class C, typename ... Ts>
struct template_traits<C<Ts...>>
{
    template <typename ... Us>
    using template_type = C<Us...>;
};

And then, argument deduction is:

// Class template argument deduction guide
template <class... Types>
template_pack(Types&&...)
-> template_pack<template_traits<std::decay_t<Types>>::template template_type...>;

Demo

Issue is that aliases are not really identical (gcc considers some aliases as identical contrary to clang) (I opened a question for that BTW)

template_traits<std::vector>::template_type is not std::vector even if for any T, A, template_traits<std::vector>::template_type<T, A> is not std::vector<T, A>.