error: you are implementing `Iterator` on a `Copy` type
  --> $DIR/copy_iterator.rs:6:1
   |
LL | / impl Iterator for Countdown {
LL | |     type Item = u8;
LL | |
LL | |     fn next(&mut self) -> Option<u8> {
...  |
LL | |     }
LL | | }
   | |_^
   |
   = note: consider implementing `IntoIterator` instead
   = note: `-D clippy::copy-iterator` implied by `-D warnings`

error: aborting due to previous error