# Enum std::collections::hash_map::Entry

1.0.0 · source ·

    pub enum Entry<'a, K: 'a, V: 'a> {
        Occupied(OccupiedEntry<'a, K, V>),
        Vacant(VacantEntry<'a, K, V>),
    }

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`.

## Variants§

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

An occupied entry.

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

A vacant entry.

## Implementations§

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### impl<'a, K, V> Entry<'a, K, V>

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#### pub fn or_insert(self, default: V) -> &'a mut V

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 std::collections::HashMap;

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

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

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

Run
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#### pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V

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 std::collections::HashMap;

    let mut map = HashMap::new();
    let value = "hoho";

    map.entry("poneyland").or_insert_with(|| value);

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

Run
1.50.0 · source

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

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 std::collections::HashMap;

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

    map.entry("poneyland").or_insert_with_key(|key| key.chars().count());

    assert_eq!(map["poneyland"], 9);

Run
1.10.0 · source

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

Returns a reference to this entry’s key.

##### Examples

    use std::collections::HashMap;

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

Run
1.26.0 · source

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

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

##### Examples

    use std::collections::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);

Run
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#### pub fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V>

🔬This is a nightly-only experimental API. (`entry_insert` #65225)

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

##### Examples

    #![feature(entry_insert)]
    use std::collections::HashMap;

    let mut map: HashMap<&str, String> = HashMap::new();
    let entry = map.entry("poneyland").insert_entry("hoho".to_string());

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

Run
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### impl<'a, K, V: Default> Entry<'a, K, V>

1.28.0 · source

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

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 std::collections::HashMap;

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

    assert_eq!(map["poneyland"], None);

Run

## Trait Implementations§

1.12.0 · source§

### impl<K: Debug, V: Debug> Debug for Entry<'_, K, V>

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

Formats the value using the given formatter. Read more

## Auto Trait Implementations§

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### impl<'a, K, V> RefUnwindSafe for Entry<'a, K, V>where K: RefUnwindSafe, V: RefUnwindSafe,

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

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

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

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### impl<'a, K, V> !UnwindSafe for Entry<'a, K, V>

## Blanket Implementations§

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### impl<T> Any for Twhere 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 Twhere T: ?Sized,

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

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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#### 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

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

Returns the argument unchanged.

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

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#### 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 Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### 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 Twhere U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.