mut_closure.rs

fn make_counter<T, Identity>(init: T, step: Identity) -> impl FnMut() -> T
where
  Identity: Clone,
  T: std::ops::AddAssign<Identity> + Clone,
{
  let mut counter = init;
  move || {
    let to_return = counter.clone();
    counter += step.clone();
    to_return
  }
}
  

fn main() {
  let mut counter = make_counter(0, 1);
  println!("{}", counter());
  println!("{}", counter());
  println!("{}", counter());
}