#![allow(unused_variables)]
#![feature(btree_set_entry)]
fn main() {
    use std::collections::btree_set::{Entry, BTreeSet};
    let mut set = BTreeSet::new();
    match set.entry("poneyland") {
        Entry::Occupied(_) => panic!(),
        Entry::Vacant(v) => assert_eq!(v.into_value(), "poneyland"),
    }
}