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