Method iter

publication/code/chapter04/list_stack.rs:84–86

(&self)

    }

    fn iter(&self) -> Iter<T> {
        Iter { next: self.top.as_deref() }
    }

    fn iter_mut(&mut self) -> IterMut<T> {
        IterMut { next: self.top.as_deref_mut() }