1 `impl Trait` is not allowed in path parameters.
3 Erroneous code example:
6 fn some_fn(mut x: impl Iterator) -> <impl Iterator>::Item { // error!
11 You cannot use `impl Trait` in path parameters. If you want something
12 equivalent, you can do this instead:
15 fn some_fn<T: Iterator>(mut x: T) -> T::Item { // ok!