# Struct hashbrown::hash_map::VacantEntryRef

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

Expand description

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

## Examples

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

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

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

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

## Implementations

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### impl<'a, 'b, K, Q: ?Sized, V, S, A: Allocator + Clone> VacantEntryRef<'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 that would be used when inserting a value through the `VacantEntryRef`.

##### Examples

    use hashbrown::HashMap;

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

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#### pub fn into_key(self) -> K where
K: From<&'b Q>,

Take ownership of the key.

##### Examples

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

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

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

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#### pub fn insert(self, value: V) -> &'a mut V where
K: Hash + From<&'b Q>,
S: BuildHasher,

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

##### Examples

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

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

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

## Trait Implementations

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

## Auto Trait Implementations

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

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

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

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