#![allow(unused_variables)]
#![feature(btree_set_entry)]
fn main() {
    use std::collections::BTreeSet;
    let mut set = BTreeSet::new();
    set.entry("poneyland").or_insert();
    assert!(set.contains("poneyland"));
    set.entry("poneyland").or_insert();
    assert!(set.contains("poneyland"));
    assert_eq!(set.len(), 1);
}