Enum std::collections::btree_map::Entry

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>),
}

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

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

A vacant entry.

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

An occupied entry.

Implementations

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

where K: Ord, A: Allocator + Clone,

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);

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

where 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());

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

where 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);

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");

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);

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

where K: Ord, V: Default, A: Allocator + Clone,

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

impl<K, V, A> Debug for Entry<'_, K, V, A>

where K: Debug + Ord, V: Debug, A: Allocator + Clone,

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

Formats the value using the given formatter.