C++17 STL Cookbook

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);

2. 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 + ...);      }

3. We can now call it this way:

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

4. It does not only work with int types; we can call it with any type that just implements the ...