list_test.rs:35:16: 35:20 error: use of moved value: `list`

list_test.rs

enum List<T> {
    Cons(T, ~List<T>),
    Empty
}

fn length<T>(xs: &List<T>) -> uint {
  match *xs {
    Empty => 0,
    Cons(_, ref rest) => 1 + length(*rest)
  }
}

fn prepend<T>(xs: List<T>, value: T) -> List<T> {
  Cons(value, ~xs)
}

fn head<T>(xs: &List<T>) -> Option<T> {
  match *xs {
    Cons(ref value, _) => Some(*value),
    _ => None
  }
}

#[test]
fn test_length() {
  let mut list: List<int> = Empty::<int>;
  list = prepend(list, 1);
  list = prepend(list, 2);

  let list_len = length(&list);
  assert_eq!(list_len, 2);
  let h = head(&list);
  assert_eq!(h, Some(2));
}

output.txt

/Users/pzol/Dropbox/src/rust/one/src/list_test.rs:22:32: 22:38 error: cannot move out of dereference of & pointer
/Users/pzol/Dropbox/src/rust/one/src/list_test.rs:22     Cons(ref value, _) => Some(*value),
                                                                                    ^~~~~~