# Struct hashbrown::hash_map::RawVacantEntryMut

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

Expand description

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

## Examples

    use core::hash::{BuildHasher, Hash};
    use hashbrown::hash_map::{HashMap, RawEntryMut, RawVacantEntryMut};

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

    fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
        use core::hash::Hasher;
        let mut state = hash_builder.build_hasher();
        key.hash(&mut state);
        state.finish()
    }

    let raw_v: RawVacantEntryMut<_, _, _> = match map.raw_entry_mut().from_key(&"a") {
        RawEntryMut::Vacant(view) => view,
        RawEntryMut::Occupied(_) => unreachable!(),
    };
    raw_v.insert("a", 10);
    assert!(map[&"a"] == 10 && map.len() == 1);

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

    let hash = compute_hash(map.hasher(), &"c");
    match map.raw_entry_mut().from_hash(hash, |q| *q == "c") {
        RawEntryMut::Occupied(_) => unreachable!(),
        RawEntryMut::Vacant(view) => {
            assert_eq!(view.insert("c", 30), (&mut "c", &mut 30));
        }
    }
    assert!(map[&"c"] == 30 && map.len() == 3);

## Implementations

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

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#### pub fn insert(self, key: K, value: V) -> (&'a mut K, &'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::hash_map::{HashMap, RawEntryMut};

    let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();

    match map.raw_entry_mut().from_key(&"c") {
        RawEntryMut::Occupied(_) => panic!(),
        RawEntryMut::Vacant(v) => assert_eq!(v.insert("c", 300), (&mut "c", &mut 300)),
    }

    assert_eq!(map[&"c"], 300);

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#### pub fn insert_hashed_nocheck(
self,
hash: u64,
key: K,
value: V
) -> (&'a mut K, &'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 core::hash::{BuildHasher, Hash};
    use hashbrown::hash_map::{HashMap, RawEntryMut};

    fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
        use core::hash::Hasher;
        let mut state = hash_builder.build_hasher();
        key.hash(&mut state);
        state.finish()
    }

    let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
    let key = "c";
    let hash = compute_hash(map.hasher(), &key);

    match map.raw_entry_mut().from_key_hashed_nocheck(hash, &key) {
        RawEntryMut::Occupied(_) => panic!(),
        RawEntryMut::Vacant(v) => assert_eq!(
            v.insert_hashed_nocheck(hash, key, 300),
            (&mut "c", &mut 300)
        ),
    }

    assert_eq!(map[&"c"], 300);

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#### pub fn insert_with_hasher<H>(
self,
hash: u64,
key: K,
value: V,
hasher: H
) -> (&'a mut K, &'a mut V) where
H: Fn(&K) -> u64,

Set the value of an entry with a custom hasher function.

##### Examples

    use core::hash::{BuildHasher, Hash};
    use hashbrown::hash_map::{HashMap, RawEntryMut};

    fn make_hasher<K, S>(hash_builder: &S) -> impl Fn(&K) -> u64 + '_
    where
        K: Hash + ?Sized,
        S: BuildHasher,
    {
        move |key: &K| {
            use core::hash::Hasher;
            let mut state = hash_builder.build_hasher();
            key.hash(&mut state);
            state.finish()
        }
    }

    let mut map: HashMap<&str, u32> = HashMap::new();
    let key = "a";
    let hash_builder = map.hasher().clone();
    let hash = make_hasher(&hash_builder)(&key);

    match map.raw_entry_mut().from_hash(hash, |q| q == &key) {
        RawEntryMut::Occupied(_) => panic!(),
        RawEntryMut::Vacant(v) => assert_eq!(
            v.insert_with_hasher(hash, key, 100, make_hasher(&hash_builder)),
            (&mut "a", &mut 100)
        ),
    }
    map.extend([("b", 200), ("c", 300), ("d", 400), ("e", 500), ("f", 600)]);
    assert_eq!(map[&"a"], 100);

## Trait Implementations

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

source

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

Formats the value using the given formatter. Read more

## Auto Trait Implementations

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

### impl<'a, K, V, S, A> Send for RawVacantEntryMut<'a, K, V, S, A> where
A: Send,
K: Send,
S: Sync,
V: Send,

### impl<'a, K, V, S, A> Sync for RawVacantEntryMut<'a, K, V, S, A> where
A: Sync,
K: Sync,
S: Sync,
V: Sync,

### impl<'a, K, V, S, A> Unpin for RawVacantEntryMut<'a, K, V, S, A>

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