# Enum hashbrown::hash_map::Entry

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    pub enum Entry<'a, K, V, S, A = Global> where
        A: Allocator + Clone, {
        Occupied(OccupiedEntry<'a, K, V, S, A>),
        Vacant(VacantEntry<'a, K, V, S, A>),
    }

Expand description

A view into a single entry in a map, which may either be vacant or occupied.

This `enum` is constructed from the `entry` method on `HashMap`.

## Examples

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

    let mut map = HashMap::new();
    map.extend([("a", 10), ("b", 20), ("c", 30)]);
    assert_eq!(map.len(), 3);

    // Existing key (insert)
    let entry: Entry<_, _, _> = map.entry("a");
    let _raw_o: OccupiedEntry<_, _, _> = entry.insert(1);
    assert_eq!(map.len(), 3);
    // Nonexistent key (insert)
    map.entry("d").insert(4);

    // Existing key (or_insert)
    let v = map.entry("b").or_insert(2);
    assert_eq!(std::mem::replace(v, 2), 20);
    // Nonexistent key (or_insert)
    map.entry("e").or_insert(5);

    // Existing key (or_insert_with)
    let v = map.entry("c").or_insert_with(|| 3);
    assert_eq!(std::mem::replace(v, 3), 30);
    // Nonexistent key (or_insert_with)
    map.entry("f").or_insert_with(|| 6);

    println!("Our HashMap: {:?}", map);

    let mut vec: Vec<_> = map.iter().map(|(&k, &v)| (k, v)).collect();
    // The `Iter` iterator produces items in arbitrary order, so the
    // items must be sorted to test them against a sorted array.
    vec.sort_unstable();
    assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3), ("d", 4), ("e", 5), ("f", 6)]);

## Variants

### `Occupied(OccupiedEntry<'a, K, V, S, A>)`

An occupied entry.

#### Examples

    use hashbrown::hash_map::{Entry, HashMap};
    let mut map: HashMap<_, _> = [("a", 100), ("b", 200)].into();

    match map.entry("a") {
        Entry::Vacant(_) => unreachable!(),
        Entry::Occupied(_) => { }
    }

### `Vacant(VacantEntry<'a, K, V, S, A>)`

A vacant entry.

#### Examples

    use hashbrown::hash_map::{Entry, HashMap};
    let mut map: HashMap<&str, i32> = HashMap::new();

    match map.entry("a") {
        Entry::Occupied(_) => unreachable!(),
        Entry::Vacant(_) => { }
    }

## Implementations

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

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#### pub fn insert(self, value: V) -> OccupiedEntry<'a, K, V, S, A> where
K: Hash,
S: BuildHasher,

Sets the value of the entry, and returns an OccupiedEntry.

##### Examples

    use hashbrown::HashMap;

    let mut map: HashMap<&str, u32> = HashMap::new();
    let entry = map.entry("horseyland").insert(37);

    assert_eq!(entry.key(), &"horseyland");

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#### pub fn or_insert(self, default: V) -> &'a mut V where
K: Hash,
S: BuildHasher,

Ensures a value is in the entry by inserting the default if empty, and returns a mutable reference to the value in the entry.

##### Examples

    use hashbrown::HashMap;

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

    // nonexistent key
    map.entry("poneyland").or_insert(3);
    assert_eq!(map["poneyland"], 3);

    // existing key
    *map.entry("poneyland").or_insert(10) *= 2;
    assert_eq!(map["poneyland"], 6);

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#### pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V where
K: Hash,
S: BuildHasher,

Ensures a value is in the entry by inserting the result of the default function if empty, and returns a mutable reference to the value in the entry.

##### Examples

    use hashbrown::HashMap;

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

    // nonexistent key
    map.entry("poneyland").or_insert_with(|| 3);
    assert_eq!(map["poneyland"], 3);

    // existing key
    *map.entry("poneyland").or_insert_with(|| 10) *= 2;
    assert_eq!(map["poneyland"], 6);

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#### pub fn or_insert_with_key<F: FnOnce(&K) -> V>(self, default: F) -> &'a mut V where
K: Hash,
S: BuildHasher,

Ensures a value is in the entry by inserting, if empty, the result of the default function. This method allows for generating key-derived values for insertion by providing the default function a reference to the key that was moved during the `.entry(key)` method call.

The reference to the moved key is provided so that cloning or copying the key is unnecessary, unlike with `.or_insert_with(|| ... )`.

##### Examples

    use hashbrown::HashMap;

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

    // nonexistent key
    map.entry("poneyland").or_insert_with_key(|key| key.chars().count());
    assert_eq!(map["poneyland"], 9);

    // existing key
    *map.entry("poneyland").or_insert_with_key(|key| key.chars().count() * 10) *= 2;
    assert_eq!(map["poneyland"], 18);

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

Returns a reference to this entry’s key.

##### Examples

    use hashbrown::HashMap;

    let mut map: HashMap<&str, u32> = HashMap::new();
    map.entry("poneyland").or_insert(3);
    // existing key
    assert_eq!(map.entry("poneyland").key(), &"poneyland");
    // nonexistent key
    assert_eq!(map.entry("horseland").key(), &"horseland");

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#### pub fn and_modify<F>(self, f: F) -> Self where
F: FnOnce(&mut V),

Provides in-place mutable access to an occupied entry before any potential inserts into the map.

##### Examples

    use hashbrown::HashMap;

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

    map.entry("poneyland")
       .and_modify(|e| { *e += 1 })
       .or_insert(42);
    assert_eq!(map["poneyland"], 42);

    map.entry("poneyland")
       .and_modify(|e| { *e += 1 })
       .or_insert(42);
    assert_eq!(map["poneyland"], 43);

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#### pub fn and_replace_entry_with<F>(self, f: F) -> Self where
F: FnOnce(&K, V) -> Option<V>,

Provides shared access to the key and owned access to the value of an occupied 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();

    let entry = map
        .entry("poneyland")
        .and_replace_entry_with(|_k, _v| panic!());

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

    map.insert("poneyland", 42);

    let entry = map
        .entry("poneyland")
        .and_replace_entry_with(|k, v| {
            assert_eq!(k, &"poneyland");
            assert_eq!(v, 42);
            Some(v + 1)
        });

    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 = map
        .entry("poneyland")
        .and_replace_entry_with(|_k, _v| None);

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

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

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

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#### pub fn or_default(self) -> &'a mut V where
K: Hash,
S: BuildHasher,

Ensures a value is in the entry by inserting the default value if empty, and returns a mutable reference to the value in the entry.

##### Examples

    use hashbrown::HashMap;

    let mut map: HashMap<&str, Option<u32>> = HashMap::new();

    // nonexistent key
    map.entry("poneyland").or_default();
    assert_eq!(map["poneyland"], None);

    map.insert("horseland", Some(3));

    // existing key
    assert_eq!(map.entry("horseland").or_default(), &mut Some(3));

## Trait Implementations

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### impl<K: Debug, V: Debug, S, A: Allocator + Clone> Debug for Entry<'_, K, 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, K, V, S, A> RefUnwindSafe for Entry<'a, K, V, S, A> where
A: RefUnwindSafe,
K: RefUnwindSafe,
S: RefUnwindSafe,
V: RefUnwindSafe,

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

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

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

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