{"ast_node_type":"other","tokens":[{"end":79,"kind":"keyword","start":0,"text":"Self::index(start).checked_add(u).map(Self::from_usize)"}]}
                        Self::index(start).checked_add(u).map(Self::from_usize)
                    fn forward_checked(start: Self, u: usize) -> Option<Self> {
                    }