Check for arguments type in a variadic template declaration

Question

I got a plain variadic template declaration, just like the classic one:

template 
class VariadicTemplate;

What

Answer 1

struct Foo {};

#include 

template
struct are_same : std::true_type
{};

template
struct are_same
    : std::integral_constant{} && are_same{}>
{};

template
class VariadicTemplate
{
    static_assert(are_same{}, "a meaningful error message");
};

int main()
{
    VariadicTemplate v0{}; (void)v0;
    VariadicTemplate v1{}; (void)v1;
}

But something tells me you want to know if the arguments are all specializations of a class template Foo:

template
struct Foo {};

#include 

template class T, class U>
struct is_template_of
{
    template
    static std::true_type test(T*);

    static std::false_type test(...);

    constexpr static bool value = decltype(test((U*)nullptr)){};
};

template class T, class...>
struct is_template_of_N : std::true_type
{};

template class T, class U, class... TT>
struct is_template_of_N
    : std::integral_constant::value
                                   && is_template_of_N{}>
{};

template
class VariadicTemplate
{
    static_assert(is_template_of_N{},
                  "a meaningful error message");
};

int main()
{
    VariadicTemplate, Foo> v0; (void)v0;
    VariadicTemplate, int> v1; (void)v1;
}