How to do it...

Let's implement a function that takes arbitrarily many parameters and returns their sum:

1. At first, we define its signature:

 template <typename ... Ts>
 auto sum(Ts ... ts);

1. So, we have a parameter pack ts now, and the function should expand all the parameters and sum them together using a fold expression. If we use any operator (+, in this example) together with ... in order to apply it to all the values of a parameter pack, we need to surround the expression with parentheses:

 template <typename ... Ts>
 auto sum(Ts ... ts)
 {
 return (ts + ...);
 }

1. We can now call it this way:

      int the_sum {sum(1, 2, 3, 4, 5)}; // Value: 15

1. It does not only work with int types; we can call it with any type that just implements the + operator, such as std::string:

 std::string a {"Hello "};
 std::string b {"World"};
 
 std::cout << sum(a, b) << '\n'; // Output: Hello World