Use fold expressions for variadic tuples

The std::tuple class is essentially a more complex, and less convenient, struct. The interface for tuple is cumbersome, although class template argument deduction and structured binding have made it somewhat easier.

I tend to use struct before tuple for most applications, with one significant exception: the one real advantage of tuple is that it can be used with fold expressions in a variadic context.

Fold expressions

Designed to make it easier to expand a variadic parameter pack, fold expressions are a new feature with C++17. Prior to fold expressions, expanding a parameter pack required a recursive function:

template<typename T>
void f(T final) {
    cout << final << '\n';
}
template<typename T, typename... Args>
void f(T first, Args... args) {
    cout << first;
    f(args...);
}
int main() {
    f("hello...