error[E0072]: recursive type `ListNode` has infinite size --> $DIR/E0072.rs:1:1 | LL | struct ListNode { | ^^^^^^^^^^^^^^^ recursive type has infinite size LL | head: u8, LL | tail: Option, | ---------------- recursive without indirection | help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `ListNode` representable | LL | tail: Option>, | ++++ + error: aborting due to previous error For more information about this error, try `rustc --explain E0072`.