Enum hashbrown::hash_map::Entry

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

§Examples

use hashbrown::hash_map::{Entry, HashMap, OccupiedEntry};

let mut map = HashMap::new();
map.extend([("a", 10), ("b", 20), ("c", 30)]);
assert_eq!(map.len(), 3);

// Existing key (insert)
let entry: Entry<_, _, _> = map.entry("a");
let _raw_o: OccupiedEntry<_, _, _> = entry.insert(1);
assert_eq!(map.len(), 3);
// Nonexistent key (insert)
map.entry("d").insert(4);

// Existing key (or_insert)
let v = map.entry("b").or_insert(2);
assert_eq!(std::mem::replace(v, 2), 20);
// Nonexistent key (or_insert)
map.entry("e").or_insert(5);

// Existing key (or_insert_with)
let v = map.entry("c").or_insert_with(|| 3);
assert_eq!(std::mem::replace(v, 3), 30);
// Nonexistent key (or_insert_with)
map.entry("f").or_insert_with(|| 6);

println!("Our HashMap: {:?}", map);

let mut vec: Vec<_> = map.iter().map(|(&k, &v)| (k, v)).collect();
// The `Iter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3), ("d", 4), ("e", 5), ("f", 6)]);

Variants§

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

An occupied entry.

§Examples

use hashbrown::hash_map::{Entry, HashMap};
let mut map: HashMap<_, _> = [("a", 100), ("b", 200)].into();

match map.entry("a") {
    Entry::Vacant(_) => unreachable!(),
    Entry::Occupied(_) => { }
}

§

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

A vacant entry.

§Examples

use hashbrown::hash_map::{Entry, HashMap};
let mut map: HashMap<&str, i32> = HashMap::new();

match map.entry("a") {
    Entry::Occupied(_) => unreachable!(),
    Entry::Vacant(_) => { }
}

Implementations§

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

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pub fn insert(self, value: V) -> OccupiedEntry<'a, K, V, S, A>
where K: Hash, S: BuildHasher,

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

§Examples

use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();
let entry = map.entry("horseyland").insert(37);

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

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pub fn or_insert(self, default: V) -> &'a mut V
where K: Hash, S: BuildHasher,

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 hashbrown::HashMap;

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

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

// existing key
*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
where K: Hash, S: BuildHasher,

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 hashbrown::HashMap;

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

// nonexistent key
map.entry("poneyland").or_insert_with(|| 3);
assert_eq!(map["poneyland"], 3);

// existing key
*map.entry("poneyland").or_insert_with(|| 10) *= 2;
assert_eq!(map["poneyland"], 6);

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

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 hashbrown::HashMap;

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

// nonexistent key
map.entry("poneyland").or_insert_with_key(|key| key.chars().count());
assert_eq!(map["poneyland"], 9);

// existing key
*map.entry("poneyland").or_insert_with_key(|key| key.chars().count() * 10) *= 2;
assert_eq!(map["poneyland"], 18);

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pub fn key(&self) -> &K

Returns a reference to this entry’s key.

§Examples

use hashbrown::HashMap;

let mut map: HashMap<&str, u32> = HashMap::new();
map.entry("poneyland").or_insert(3);
// existing key
assert_eq!(map.entry("poneyland").key(), &"poneyland");
// nonexistent key
assert_eq!(map.entry("horseland").key(), &"horseland");

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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 hashbrown::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 and_replace_entry_with<F>(self, f: F) -> Self
where F: FnOnce(&K, V) -> Option<V>,

Provides shared access to the key and owned access to the value of an occupied entry and allows to replace or remove it based on the value of the returned option.

§Examples

use hashbrown::HashMap;
use hashbrown::hash_map::Entry;

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

let entry = map
    .entry("poneyland")
    .and_replace_entry_with(|_k, _v| panic!());

match entry {
    Entry::Vacant(e) => {
        assert_eq!(e.key(), &"poneyland");
    }
    Entry::Occupied(_) => panic!(),
}

map.insert("poneyland", 42);

let entry = map
    .entry("poneyland")
    .and_replace_entry_with(|k, v| {
        assert_eq!(k, &"poneyland");
        assert_eq!(v, 42);
        Some(v + 1)
    });

match entry {
    Entry::Occupied(e) => {
        assert_eq!(e.key(), &"poneyland");
        assert_eq!(e.get(), &43);
    }
    Entry::Vacant(_) => panic!(),
}

assert_eq!(map["poneyland"], 43);

let entry = map
    .entry("poneyland")
    .and_replace_entry_with(|_k, _v| None);

match entry {
    Entry::Vacant(e) => assert_eq!(e.key(), &"poneyland"),
    Entry::Occupied(_) => panic!(),
}

assert!(!map.contains_key("poneyland"));

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

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pub fn or_default(self) -> &'a mut V
where K: Hash, S: BuildHasher,

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 hashbrown::HashMap;

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

// nonexistent key
map.entry("poneyland").or_default();
assert_eq!(map["poneyland"], None);

map.insert("horseland", Some(3));

// existing key
assert_eq!(map.entry("horseland").or_default(), &mut Some(3));