linked_list_setter2.rs

// setter methods (by index)
impl<T> LinkedList<T> {
    /// Insert node to i-th index of LinkedList.
    /// If given index if bigger than length of LinkedList,
    /// Node will be attached to the tail of LinkedList
    #[inline]
    pub fn insert(&mut self, val: T, index: u32) {
        self.insert_node(Box::new(Node::new(val)), index)
    }

    #[inline]
    fn insert_node(&mut self, mut node: Box<Node<T>>, index: u32) {
        if index > self.length {
            return self.push_back_node(node);
        }

        if index == 0 {
            return self.push_front_node(node);
        }

        unsafe {
            let mut front = self.get_ith_node(self.head, index - 1).unwrap(); // None is unreachable
            let back = front.as_ref().next;

            // [front] -> [middle] -> [back]
            node.next = back;
            let middle = NonNull::new_unchecked(Box::into_raw(node));
            front.as_mut().next = Some(middle);
        }

        self.length += 1;
    }
}