The error returned by try_insert when the key already exists.

Contains the occupied entry, and the value that was not inserted.

Examples

use hashbrown::hash_map::{HashMap, OccupiedError};

let mut map: HashMap<_, _> = [("a", 10), ("b", 20)].into();

// try_insert method returns mutable reference to the value if keys are vacant,
// but if the map did have key present, nothing is updated, and the provided
// value is returned inside `Err(_)` variant
match map.try_insert("a", 100) {
    Err(OccupiedError { mut entry, value }) => {
        assert_eq!(entry.key(), &"a");
        assert_eq!(value, 100);
        assert_eq!(entry.insert(100), 10)
    }
    _ => unreachable!(),
}
assert_eq!(map[&"a"], 100);