#![allow(unused_variables)]
fn main() {
    use std::collections::BTreeMap;
    let mut map: BTreeMap<&str, usize> = BTreeMap::new();
    map.entry("poneyland").and_modify(|e| { *e += 1 }).or_insert(42);
    assert_eq!(map["poneyland"], 42);
    map.entry("poneyland").and_modify(|e| { *e += 1 }).or_insert(42);
    assert_eq!(map["poneyland"], 43);
}