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