error: you are implementing `Iterator` on a `Copy` type
  --> $DIR/copy_iterator.rs:18:1
   |
18 | / impl Iterator for Countdown {
19 | |     type Item = u8;
20 | |
21 | |     fn next(&mut self) -> Option<u8> {
...  |
26 | |     }
27 | | }
   | |_^
   |
   = note: `-D clippy::copy-iterator` implied by `-D warnings`
   = note: consider implementing `IntoIterator` instead

error: aborting due to previous error