# Struct hashbrown::hash_map::OccupiedEntry

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

Expand description

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

## Examples

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

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

    let _entry_o: OccupiedEntry<_, _, _> = map.entry("a").insert(100);
    assert_eq!(map.len(), 3);

    // Existing key (insert and update)
    match map.entry("a") {
        Entry::Vacant(_) => unreachable!(),
        Entry::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("c") {
        Entry::Vacant(_) => unreachable!(),
        Entry::Occupied(view) => {
            assert_eq!(view.remove_entry(), ("c", 30));
        }
    }
    assert_eq!(map.get(&"c"), None);
    assert_eq!(map.len(), 2);

## Implementations

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### impl<'a, K, V, S, A: Allocator + Clone> OccupiedEntry<'a, K, V, S, A>

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#### pub fn key(&self) -> &K

Gets a reference to the key in the entry.

##### Examples

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

    let mut map: HashMap<&str, u32> = HashMap::new();
    map.entry("poneyland").or_insert(12);

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

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#### 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::Entry;

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

    map.entry("poneyland").or_insert(12);
    let capacity_before_remove = map.capacity();

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

    assert_eq!(map.contains_key("poneyland"), false);
    // Now map hold none elements but capacity is equal to the old one
    assert!(map.len() == 0 && map.capacity() == capacity_before_remove);

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#### pub fn get(&self) -> &V

Gets a reference to the value in the entry.

##### Examples

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

    let mut map: HashMap<&str, u32> = HashMap::new();
    map.entry("poneyland").or_insert(12);

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

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#### 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 `OccupiedEntry` which may outlive the destruction of the `Entry` value, see `into_mut`.

##### Examples

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

    let mut map: HashMap<&str, u32> = HashMap::new();
    map.entry("poneyland").or_insert(12);

    assert_eq!(map["poneyland"], 12);
    if let Entry::Occupied(mut o) = map.entry("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);

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

Converts the OccupiedEntry 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 `OccupiedEntry`, see `get_mut`.

##### Examples

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

    let mut map: HashMap<&str, u32> = HashMap::new();
    map.entry("poneyland").or_insert(12);

    assert_eq!(map["poneyland"], 12);

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

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

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#### 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::Entry;

    let mut map: HashMap<&str, u32> = HashMap::new();
    map.entry("poneyland").or_insert(12);

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

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

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#### 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::Entry;

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

    map.entry("poneyland").or_insert(12);
    let capacity_before_remove = map.capacity();

    if let Entry::Occupied(o) = map.entry("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.len() == 0 && map.capacity() == capacity_before_remove);

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

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 OccupiedEntry was created through `Entry::insert`.

##### Examples

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

     let mut map: HashMap<Rc<String>, u32> = HashMap::new();
     let key_one = Rc::new("Stringthing".to_string());
     let key_two = Rc::new("Stringthing".to_string());

     map.insert(key_one.clone(), 15);
     assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);

     match map.entry(key_two.clone()) {
         Entry::Occupied(entry) => {
             let (old_key, old_value): (Rc<String>, u32) = entry.replace_entry(16);
             assert!(Rc::ptr_eq(&key_one, &old_key) && old_value == 15);
         }
         Entry::Vacant(_) => panic!(),
     }

     assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
     assert_eq!(map[&"Stringthing".to_owned()], 16);

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#### pub fn replace_key(self) -> K

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

##### Panics

Will panic if this OccupiedEntry was created through `Entry::insert`.

##### Examples

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

    let mut map: HashMap<Rc<String>, usize> = HashMap::with_capacity(6);
    let mut keys_one: Vec<Rc<String>> = Vec::with_capacity(6);
    let mut keys_two: Vec<Rc<String>> = Vec::with_capacity(6);

    for (value, key) in ["a", "b", "c", "d", "e", "f"].into_iter().enumerate() {
        let rc_key = Rc::new(key.to_owned());
        keys_one.push(rc_key.clone());
        map.insert(rc_key.clone(), value);
        keys_two.push(Rc::new(key.to_owned()));
    }

    assert!(
        keys_one.iter().all(|key| Rc::strong_count(key) == 2)
            && keys_two.iter().all(|key| Rc::strong_count(key) == 1)
    );

    reclaim_memory(&mut map, &keys_two);

    assert!(
        keys_one.iter().all(|key| Rc::strong_count(key) == 1)
            && keys_two.iter().all(|key| Rc::strong_count(key) == 2)
    );

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

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#### pub fn replace_entry_with<F>(self, f: F) -> Entry<'a, K, 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::Entry;

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

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

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

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

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

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

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

## Trait Implementations

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### impl<K: Debug, V: Debug, S, A: Allocator + Clone> Debug for OccupiedEntry<'_, K, V, S, A>

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

Formats the value using the given formatter. Read more

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### impl<K, V, S, A> Send for OccupiedEntry<'_, K, V, S, A> where
K: Send,
V: Send,
S: Send,
A: Send + Allocator + Clone,

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### impl<K, V, S, A> Sync for OccupiedEntry<'_, K, V, S, A> where
K: Sync,
V: Sync,
S: Sync,
A: Sync + Allocator + Clone,

## Auto Trait Implementations

### impl<'a, K, V, S, A> RefUnwindSafe for OccupiedEntry<'a, K, V, S, A> where
A: RefUnwindSafe,
K: RefUnwindSafe,
S: RefUnwindSafe,
V: RefUnwindSafe,

### impl<'a, K, V, S, A> Unpin for OccupiedEntry<'a, K, V, S, A> where
K: Unpin,

### impl<'a, K, V, S, A = Global> !UnwindSafe for OccupiedEntry<'a, K, V, S, A>

## Blanket Implementations

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### impl<T> Any for T where
T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more

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### impl<T> Borrow<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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### impl<T> BorrowMut<T> for T where
T: ?Sized,

const: unstable · source

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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### impl<T> From<T> for T

const: unstable · source

#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T where
U: From<T>,

const: unstable · source

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

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### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.