Struct hashbrown::hash_map::OccupiedEntryRef

pub struct OccupiedEntryRef<'a, 'b, K, Q: ?Sized, V, S, A: Allocator = Global> { /* private fields */ }

A view into an occupied entry in a HashMap. It is part of the EntryRef enum.

Examples

use hashbrown::hash_map::{EntryRef, HashMap, OccupiedEntryRef};

let mut map = HashMap::new();
map.extend([("a".to_owned(), 10), ("b".into(), 20), ("c".into(), 30)]);

let key = String::from("a");
let _entry_o: OccupiedEntryRef<_, _, _, _> = map.entry_ref(&key).insert(100);
assert_eq!(map.len(), 3);

// Existing key (insert and update)
match map.entry_ref("a") {
    EntryRef::Vacant(_) => unreachable!(),
    EntryRef::Occupied(mut view) => {
        assert_eq!(view.get(), &100);
        let v = view.get_mut();
        *v *= 10;
        assert_eq!(view.insert(1111), 1000);
    }
}

assert_eq!(map["a"], 1111);
assert_eq!(map.len(), 3);

// Existing key (take)
match map.entry_ref("c") {
    EntryRef::Vacant(_) => unreachable!(),
    EntryRef::Occupied(view) => {
        assert_eq!(view.remove_entry(), ("c".to_owned(), 30));
    }
}
assert_eq!(map.get("c"), None);
assert_eq!(map.len(), 2);

Implementations

impl<'a, 'b, K, Q: ?Sized, V, S, A: Allocator> OccupiedEntryRef<'a, 'b, K, Q, V, S, A>

pub fn key(&self) -> &K

Gets a reference to the key in the entry.

Examples

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

let mut map: HashMap<String, u32> = HashMap::new();
map.entry_ref("poneyland").or_insert(12);

match map.entry_ref("poneyland") {
    EntryRef::Vacant(_) => panic!(),
    EntryRef::Occupied(entry) => assert_eq!(entry.key(), "poneyland"),
}

pub fn remove_entry(self) -> (K, V)

Take the ownership of the key and value from the map. Keeps the allocated memory for reuse.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::EntryRef;

let mut map: HashMap<String, u32> = HashMap::new();
// The map is empty
assert!(map.is_empty() && map.capacity() == 0);

map.entry_ref("poneyland").or_insert(12);

if let EntryRef::Occupied(o) = map.entry_ref("poneyland") {
    // We delete the entry from the map.
    assert_eq!(o.remove_entry(), ("poneyland".to_owned(), 12));
}

assert_eq!(map.contains_key("poneyland"), false);
// Now map hold none elements but capacity is equal to the old one
assert!(map.is_empty());

pub fn get(&self) -> &V

Gets a reference to the value in the entry.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::EntryRef;

let mut map: HashMap<String, u32> = HashMap::new();
map.entry_ref("poneyland").or_insert(12);

match map.entry_ref("poneyland") {
    EntryRef::Vacant(_) => panic!(),
    EntryRef::Occupied(entry) => assert_eq!(entry.get(), &12),
}

pub fn get_mut(&mut self) -> &mut V

Gets a mutable reference to the value in the entry.

If you need a reference to the OccupiedEntryRef which may outlive the destruction of the EntryRef value, see into_mut.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::EntryRef;

let mut map: HashMap<String, u32> = HashMap::new();
map.entry_ref("poneyland").or_insert(12);

assert_eq!(map["poneyland"], 12);
if let EntryRef::Occupied(mut o) = map.entry_ref("poneyland") {
    *o.get_mut() += 10;
    assert_eq!(*o.get(), 22);

    // We can use the same Entry multiple times.
    *o.get_mut() += 2;
}

assert_eq!(map["poneyland"], 24);

pub fn into_mut(self) -> &'a mut V

Converts the OccupiedEntryRef into a mutable reference to the value in the entry with a lifetime bound to the map itself.

If you need multiple references to the OccupiedEntryRef, see get_mut.

Examples

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

let mut map: HashMap<String, u32> = HashMap::new();
map.entry_ref("poneyland").or_insert(12);

let value: &mut u32;
match map.entry_ref("poneyland") {
    EntryRef::Occupied(entry) => value = entry.into_mut(),
    EntryRef::Vacant(_) => panic!(),
}
*value += 10;

assert_eq!(map["poneyland"], 22);

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

Sets the value of the entry, and returns the entry’s old value.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::EntryRef;

let mut map: HashMap<String, u32> = HashMap::new();
map.entry_ref("poneyland").or_insert(12);

if let EntryRef::Occupied(mut o) = map.entry_ref("poneyland") {
    assert_eq!(o.insert(15), 12);
}

assert_eq!(map["poneyland"], 15);

pub fn remove(self) -> V

Takes the value out of the entry, and returns it. Keeps the allocated memory for reuse.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::EntryRef;

let mut map: HashMap<String, u32> = HashMap::new();
// The map is empty
assert!(map.is_empty() && map.capacity() == 0);

map.entry_ref("poneyland").or_insert(12);

if let EntryRef::Occupied(o) = map.entry_ref("poneyland") {
    assert_eq!(o.remove(), 12);
}

assert_eq!(map.contains_key("poneyland"), false);
// Now map hold none elements but capacity is equal to the old one
assert!(map.is_empty());

pub fn replace_entry(self, value: V) -> (K, V)

where K: From<&'b Q>,

Replaces the entry, returning the old key and value. The new key in the hash map will be the key used to create this entry.

Panics

Will panic if this OccupiedEntryRef was created through EntryRef::insert.

Examples

use hashbrown::hash_map::{EntryRef, HashMap};
use std::rc::Rc;

let mut map: HashMap<Rc<str>, u32> = HashMap::new();
let key: Rc<str> = Rc::from("Stringthing");

map.insert(key.clone(), 15);
assert_eq!(Rc::strong_count(&key), 2);

match map.entry_ref("Stringthing") {
    EntryRef::Occupied(entry) => {
        let (old_key, old_value): (Rc<str>, u32) = entry.replace_entry(16);
        assert!(Rc::ptr_eq(&key, &old_key) && old_value == 15);
    }
    EntryRef::Vacant(_) => panic!(),
}

assert_eq!(Rc::strong_count(&key), 1);
assert_eq!(map["Stringthing"], 16);

pub fn replace_key(self) -> K

where K: From<&'b Q>,

Replaces the key in the hash map with the key used to create this entry.

Panics

Will panic if this OccupiedEntryRef was created through EntryRef::insert.

Examples

use hashbrown::hash_map::{EntryRef, HashMap};
use std::rc::Rc;

let mut map: HashMap<Rc<str>, usize> = HashMap::with_capacity(6);
let mut keys: Vec<Rc<str>> = Vec::with_capacity(6);

for (value, key) in ["a", "b", "c", "d", "e", "f"].into_iter().enumerate() {
    let rc_key: Rc<str> = Rc::from(key);
    keys.push(rc_key.clone());
    map.insert(rc_key.clone(), value);
}

assert!(keys.iter().all(|key| Rc::strong_count(key) == 2));

// It doesn't matter that we kind of use a vector with the same keys,
// because all keys will be newly created from the references
reclaim_memory(&mut map, &keys);

assert!(keys.iter().all(|key| Rc::strong_count(key) == 1));

fn reclaim_memory(map: &mut HashMap<Rc<str>, usize>, keys: &[Rc<str>]) {
    for key in keys {
        if let EntryRef::Occupied(entry) = map.entry_ref(key.as_ref()) {
            // Replaces the entry's key with our version of it in `keys`.
            entry.replace_key();
        }
    }
}

pub fn replace_entry_with<F>(self, f: F) -> EntryRef<'a, 'b, K, Q, V, S, A>

where F: FnOnce(&K, V) -> Option<V>,

Provides shared access to the key and owned access to the value of the entry and allows to replace or remove it based on the value of the returned option.

Examples

use hashbrown::HashMap;
use hashbrown::hash_map::EntryRef;

let mut map: HashMap<String, u32> = HashMap::new();
map.insert("poneyland".to_string(), 42);

let entry = match map.entry_ref("poneyland") {
    EntryRef::Occupied(e) => {
        e.replace_entry_with(|k, v| {
            assert_eq!(k, "poneyland");
            assert_eq!(v, 42);
            Some(v + 1)
        })
    }
    EntryRef::Vacant(_) => panic!(),
};

match entry {
    EntryRef::Occupied(e) => {
        assert_eq!(e.key(), "poneyland");
        assert_eq!(e.get(), &43);
    }
    EntryRef::Vacant(_) => panic!(),
}

assert_eq!(map["poneyland"], 43);

let entry = match map.entry_ref("poneyland") {
    EntryRef::Occupied(e) => e.replace_entry_with(|_k, _v| None),
    EntryRef::Vacant(_) => panic!(),
};

match entry {
    EntryRef::Vacant(e) => {
        assert_eq!(e.key(), "poneyland");
    }
    EntryRef::Occupied(_) => panic!(),
}

assert!(!map.contains_key("poneyland"));

Trait Implementations

impl<K: Borrow<Q>, Q: ?Sized + Debug, V: Debug, S, A: Allocator> Debug for OccupiedEntryRef<'_, '_, K, Q, V, S, A>

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

Formats the value using the given formatter.

impl<'a, 'b, K, Q, V, S, A> Send for OccupiedEntryRef<'a, 'b, K, Q, V, S, A>

where K: Send, Q: Sync + ?Sized, V: Send, S: Send, A: Send + Allocator,

impl<'a, 'b, K, Q, V, S, A> Sync for OccupiedEntryRef<'a, 'b, K, Q, V, S, A>

where K: Sync, Q: Sync + ?Sized, V: Sync, S: Sync, A: Sync + Allocator,