Correct variadic pack expansion-CodePudding

I am working on C 20 implementation of tuple:

template<size_t INDEX, typename T>
struct wrap { [[no_unique_address]] T data {}; };

template<typename...>
class base {};

template<size_t... INDEX, typename... Ts>
class base<index_sequence<INDEX...>, Ts...> : public wrap<INDEX, Ts>... {
public:
    constexpr base( const Ts &... args ) : /* !! HERE SHALL THE MAGIC COME */ {}
};

template<typename... Ts>
class tuple : public base<index_sequence_for<Ts...>, Ts...> {
public:
    /* Inherit base constructors */
    using base<index_sequence_for<Ts...>, Ts...>::base;
};

My question is: How to correctly implement the code in place of /* !! HERE SHALL THE MAGIC COME */ to call base, means wrap<> constructor - the wrap copy constructor taking the corresponding instance of T (expanded from base's template variadic pack Ts) hold in args?

Thanks in advance to anyone willing to help.

CodePudding user response：

Parameter pack expansion also applies to member initializer lists, so you can simply do this:

template<size_t INDEX, typename T>
struct wrap { [[no_unique_address]] T data {}; };

template<typename...>
class base {};

template<size_t... INDEX, typename... Ts>
class base<std::index_sequence<INDEX...>, Ts...> : public wrap<INDEX, Ts>... {
 public:
  constexpr base(const Ts&... args) : wrap<INDEX, Ts>{args}... {}
};

Demo.