Struct VacantEntry

pub struct VacantEntry<'a, K, V, S = DefaultHashBuilder, A: Allocator = Global> { /* private fields */ }

A view into a vacant entry in a HashMap. It is part of the Entry enum.

Examples

use hashbrown::hash_map::{Entry, HashMap, VacantEntry};

let mut map = HashMap::<&str, i32>::new();

let entry_v: VacantEntry<_, _, _> = match map.entry("a") {
    Entry::Vacant(view) => view,
    Entry::Occupied(_) => unreachable!(),
};
entry_v.insert(10);
assert!(map[&"a"] == 10 && map.len() == 1);

// Nonexistent key (insert and update)
match map.entry("b") {
    Entry::Occupied(_) => unreachable!(),
    Entry::Vacant(view) => {
        let value = view.insert(2);
        assert_eq!(*value, 2);
        *value = 20;
    }
}
assert!(map[&"b"] == 20 && map.len() == 2);

Implementations

impl<'a, K, V, S, A: Allocator> VacantEntry<'a, K, V, S, A>

pub fn key(&self) -> &K

Gets a reference to the key that would be used when inserting a value through the VacantEntry.

Examples

use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();
assert_eq!(map.entry("poneyland").key(), &"poneyland");

pub fn into_key(self) -> K

Take ownership of the key.

Examples

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

let mut map: HashMap<&str, u32> = HashMap::new();

match map.entry("poneyland") {
    Entry::Occupied(_) => panic!(),
    Entry::Vacant(v) => assert_eq!(v.into_key(), "poneyland"),
}

pub fn insert(self, value: V) -> &'a mut V

where K: Hash, S: BuildHasher,

Sets the value of the entry with the VacantEntry’s key, and returns a mutable reference to it.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::Entry;

let mut map: HashMap<&str, u32> = HashMap::new();

if let Entry::Vacant(o) = map.entry("poneyland") {
    o.insert(37);
}
assert_eq!(map["poneyland"], 37);

pub fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V, S, A>

where K: Hash, S: BuildHasher,

Sets the value of the entry with the VacantEntry’s key, and returns an OccupiedEntry.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::Entry;

let mut map: HashMap<&str, u32> = HashMap::new();

if let Entry::Vacant(v) = map.entry("poneyland") {
    let o = v.insert_entry(37);
    assert_eq!(o.get(), &37);
}

Trait Implementations

impl<K: Debug, V, S, A: Allocator> Debug for VacantEntry<'_, K, V, S, A>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

Layout

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.