# Struct hashbrown::hash_map::OccupiedEntryRef

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

Expand description

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

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

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#### pub fn key(&self) -> &Q where
K: Borrow<Q>,

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"),
    }

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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::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);
    let capacity_before_remove = map.capacity();

    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.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::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),
    }

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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 `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);

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#### 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);

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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::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);

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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::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);
    let capacity_before_remove = map.capacity();

    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.len() == 0 && map.capacity() == capacity_before_remove);

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#### 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 OccupiedEntry 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);

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#### 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 OccupiedEntry was created through `Entry::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();
            }
        }
    }

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#### pub fn replace_entry_with<F>(self, f: F) -> EntryRef<'a, 'b, K, Q, V, S, A> where
F: FnOnce(&Q, V) -> Option<V>,
K: Borrow<Q>,

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

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

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### 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 + Clone,

## Auto Trait Implementations

### impl<'a, 'b, K, Q: ?Sized, V, S, A> RefUnwindSafe for OccupiedEntryRef<'a, 'b, K, Q, V, S, A> where
A: RefUnwindSafe,
K: RefUnwindSafe,
Q: RefUnwindSafe,
S: RefUnwindSafe,
V: RefUnwindSafe,

### impl<'a, 'b, K, Q: ?Sized, V, S, A> Unpin for OccupiedEntryRef<'a, 'b, K, Q, V, S, A> where
K: Unpin,

### impl<'a, 'b, K, Q, V, S, A = Global> !UnwindSafe for OccupiedEntryRef<'a, 'b, K, Q, 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.