Enum std::collections::btree_map::Entry

1.0.0 · source ·
pub enum Entry<'a, K, V, A = Global>where
    K: 'a,
    V: 'a,
    A: Allocator + Clone,
{ 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§

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

A vacant entry.

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

An occupied entry.

Implementations§

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

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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::BTreeMap;

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

assert_eq!(map["poneyland"], 12);
Run
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pub fn or_insert_with<F>(self, default: F) -> &'a mut Vwhere
    F: FnOnce() -> 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());
Run
1.50.0 · source

pub fn or_insert_with_key<F>(self, default: F) -> &'a mut Vwhere
    F: FnOnce(&K) -> 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);
Run
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");
Run
1.26.0 · source

pub fn and_modify<F>(self, f: F) -> Entry<'a, K, V, A>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);
Run
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impl<'a, K, V, A> Entry<'a, K, V, A>where
    K: Ord,
    V: Default,
    A: Allocator + Clone,

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);
Run

Trait Implementations§

1.12.0 · source§

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

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

Formats the value using the given formatter. Read more

Auto Trait Implementations§

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

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

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

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

const: unstable · source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for Twhere
    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 Twhere
    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 Twhere
    U: Into<T>,

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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 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.
const: unstable · source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.