{"ast_node_type":"variable","tokens":[{"end":62,"kind":"keyword","start":0,"text":"let"}]}
    let twos: Vec<_> = set.get_by_key_enumerated(2).collect();
    // `get_by_key` returns items in insertion order.
    let idxs: Vec<usize> = twos.iter().map(|(i, _)| *i).collect();