Declare member variables from variadic template parameter

Question

Obviously the code below doesn't compile in C++. But I have a case where I'd like to parameterize a class with zero or more data items based on template parameters.

Is there any way I can declare a class whose data members depend on variadic template parameters so I can access each of them? or some other way to achieve what I'd like?

This came up in a real program which I've solved an entirely different way but now I'm interested in the more abstract problem of how I might have done this.

template <typename... Types> class Data {     // Declare a variable of each type in the parameter pack     // This is NOT valid C++ and won't compile...     Types... items; };  struct Item1 {     int a; };  struct Item2 {     float x, y, z; };  struct Item3 {     std::string name; }  int main() {     Data<Item1, Item2> data1;     Data<Item3> data2; } 

Answer 1

You could use a std::tuple

#include <tuple>  template <typename... Types> class Data {     std::tuple<Types...> items; };  struct Item1 {     int a; };  struct Item2 {     float x, y, z; };  struct Item3 {     std::string name; };  int main() {     Data<Item1, Item2> data1;     Data<Item3> data2; } 

Try it here