{"ast_node_type":"other","tokens":[{"end":56,"kind":"keyword","start":0,"text":"Some((ArenaMap::<Idx<T>,"}]}
        Some((ArenaMap::<Idx<T>, V>::from_idx(idx), o?))
    fn mapper((idx, o): (usize, Option<V>)) -> Option<(Idx<T>, V)> {
    }