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Enum std::collections::hash_map::Entry

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

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

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

An occupied entry.

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);
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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");
1.50.0source 
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);
1.10.0source 
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");
1.26.0source 
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::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 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");
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impl<'a, K, V: Default> Entry<'a, K, V>
1.28.0source 
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);

Trait Implementations

1.12.0source 
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

impl<'a, K, V> RefUnwindSafe for Entry<'a, K, V>
where
    K: RefUnwindSafe,
    V: RefUnwindSafe,
impl<'a, K, V> Send for Entry<'a, K, V>
where
    K: Send,
    V: Send,
impl<'a, K, V> Sync for Entry<'a, K, V>
where
    K: Sync,
    V: Sync,
impl<'a, K, V> Unpin for Entry<'a, K, V>
where
    K: Unpin,
impl<'a, K, V> !UnwindSafe for Entry<'a, K, V>

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>,
 
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>,
 
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.

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/collections/hash_map/enum.Entry.html