error: you are implementing `Iterator` on a `Copy` type
  --> $DIR/copy_iterator.rs:15:1
   |
15 | / impl Iterator for Countdown {
16 | |     type Item = u8;
17 | |
18 | |     fn next(&mut self) -> Option<u8> {
...  |
23 | |     }
24 | | }
   | |_^
   |
   = note: `-D clippy::copy-iterator` implied by `-D warnings`
   = note: consider implementing `IntoIterator` instead

error: aborting due to previous error