warning: method `iter_` is never used
  --> $DIR/static-impl.rs:38:8
   |
LL | trait vec_utils<T> {
   |       --------- method in this trait
LL |     fn length_(&self, ) -> usize;
LL |     fn iter_<F>(&self, f: F) where F: FnMut(&T);
   |        ^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

warning: 1 warning emitted