Why the base case with no template arguments for variadic tuple is not working?-CodePudding

As an exercise, I'm trying to define a variadic template for a Tuple but I found that the base case with no elements is not working.

template <typename Head, typename... Tail>
struct Tuple : Tuple<Tail...>
{
  Tuple(const Head& head, const Tail&... tail)
    : Base{tail...}, m_head{head} {}

private:
  using Base = Tuple<Tail...>;
  Head m_head;
};

template <> struct Tuple<> {};

MSVC 2022 gives the following error:

C:\projects\cpp\cpp_programming_language\28_metaprogramming\variadic_tuple.cpp(12): error C2976: 'Tuple': too few template arguments
  C:\projects\cpp\cpp_programming_language\28_metaprogramming\variadic_tuple.cpp(2): note: see declaration of 'Tuple'
C:\projects\cpp\cpp_programming_language\28_metaprogramming\variadic_tuple.cpp(12): error C2913: explicit specialization; 'Tuple' is not a specialization of a class template

Why this does not work and how to fix it?

CodePudding user response：

One correct incantation would be

template <typename...> struct Tuple;

template <typename Head, typename... Tail>
struct Tuple<Head, Tail...> : Tuple<Tail...>
{

(the rest is identical to your code).