#![allow(unused_variables)]
#![feature(btree_set_entry)]
fn main() {
    use std::collections::btree_set::{Entry, BTreeSet};
    let mut set = BTreeSet::new();
    set.extend(["a", "b", "c"]);
    let _entry_o = set.entry("a").insert();
    assert_eq!(set.len(), 3);
    match set.entry("a") {
        Entry::Vacant(_) => unreachable!(),
        Entry::Occupied(view) => {
            assert_eq!(view.get(), & "a");
        }
    }
    assert_eq!(set.len(), 3);
    match set.entry("c") {
        Entry::Vacant(_) => unreachable!(),
        Entry::Occupied(view) => {
            assert_eq!(view.remove(), "c");
        }
    }
    assert_eq!(set.get(& "c"), None);
    assert_eq!(set.len(), 2);
}