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