Entry in alloc::collections::btree_map - Rust
Description: A view into a single entry in a map, which may either be vacant or occupied.

## Entry

# Enum Entry

1.36.0 · Source

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

## Variants§

§1.36.0

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

A vacant entry.

§1.36.0

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

An occupied entry.

## Implementations§

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

1.0.0 · Source

#### 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::BTreeMap;

    let mut map: BTreeMap<&str, usize> = BTreeMap::new();
    map.entry("poneyland").or_insert(12);

    assert_eq!(map["poneyland"], 12);

1.0.0 · Source

#### 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::BTreeMap;

    let mut map: BTreeMap<&str, String> = BTreeMap::new();
    let s = "hoho".to_string();

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

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

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::BTreeMap;

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

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

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

1.10.0 · Source

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

Returns a reference to this entry’s key.

##### §Examples

    use std::collections::BTreeMap;

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

1.26.0 · Source

#### 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 std::collections::BTreeMap;

    let mut map: BTreeMap<&str, usize> = BTreeMap::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);

1.92.0 · Source

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

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

##### §Examples

    use std::collections::BTreeMap;

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

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

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

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::BTreeMap;

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

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

## Trait Implementations§

1.12.0 · Source§

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

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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, A> Freeze for Entry<'a, K, V, A>
where K: Freeze, A: Freeze,

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

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

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

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

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

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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 T
where 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 T
where 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 T
where 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 T
where 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.