// change `self` here, but we could replace the prefix if we wanted.
fn do_action(&mut self, digit: u64) {
unimplemented!()
// change `self` here, but we could replace the prefix if we wanted.
fn do_action(&mut self, digit: u64) {
unimplemented!()
// that can act on iterators. Try using some of them. What about a function that sums the even numbers of an iterator? Or a function that computes the
// product of those numbers that sit at odd positions? A function that checks whether a vector contains a certain number? Whether all numbers are
// smaller than some threshold? Be creative!
// that can act on iterators. Try using some of them. What about a function that sums the even numbers of an iterator? Or a function that computes the
// product of those numbers that sit at odd positions? A function that checks whether a vector contains a certain number? Whether all numbers are
// smaller than some threshold? Be creative!