Struct linked_hash_map::LinkedHashMap

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pub struct LinkedHashMap<K, V, S = RandomState> { /* private fields */ }

Expand description

A linked hash map.

Implementations§

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impl<K: Hash + Eq, V> LinkedHashMap<K, V>

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pub fn new() -> Self

Creates a linked hash map.

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pub fn with_capacity(capacity: usize) -> Self

Creates an empty linked hash map with the given initial capacity.

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impl<K: Hash + Eq, V, S: BuildHasher> LinkedHashMap<K, V, S>

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pub fn with_hasher(hash_builder: S) -> Self

Creates an empty linked hash map with the given initial hash builder.

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pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self

Creates an empty linked hash map with the given initial capacity and hash builder.

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pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more elements to be inserted into the map. The map may reserve more space to avoid frequent allocations.

§Panics

Panics if the new allocation size overflows usize.

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pub fn shrink_to_fit(&mut self)

Shrinks the capacity of the map as much as possible. It will drop down as much as possible while maintaining the internal rules and possibly leaving some space in accordance with the resize policy.

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pub fn entry(&mut self, k: K) -> Entry<'_, K, V, S>

Gets the given key’s corresponding entry in the map for in-place manipulation.

§Examples

use linked_hash_map::LinkedHashMap;

let mut letters = LinkedHashMap::new();

for ch in "a short treatise on fungi".chars() {
    let counter = letters.entry(ch).or_insert(0);
    *counter += 1;
}

assert_eq!(letters[&'s'], 2);
assert_eq!(letters[&'t'], 3);
assert_eq!(letters[&'u'], 1);
assert_eq!(letters.get(&'y'), None);

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pub fn entries(&mut self) -> Entries<'_, K, V, S> ⓘ

Returns an iterator visiting all entries in insertion order. Iterator element type is OccupiedEntry<K, V, S>. Allows for removal as well as replacing the entry.

§Examples

use linked_hash_map::LinkedHashMap;

let mut map = LinkedHashMap::new();
map.insert("a", 10);
map.insert("c", 30);
map.insert("b", 20);

{
    let mut iter = map.entries();
    let mut entry = iter.next().unwrap();
    assert_eq!(&"a", entry.key());
    *entry.get_mut() = 17;
}

assert_eq!(&17, map.get(&"a").unwrap());

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pub fn insert(&mut self, k: K, v: V) -> Option<V>

Inserts a key-value pair into the map. If the key already existed, the old value is returned.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();

map.insert(1, "a");
map.insert(2, "b");
assert_eq!(map[&1], "a");
assert_eq!(map[&2], "b");

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pub fn contains_key<Q>(&self, k: &Q) -> bool
where K: Borrow<Q>, Q: Eq + Hash + ?Sized,

Checks if the map contains the given key.

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pub fn get<Q>(&self, k: &Q) -> Option<&V>
where K: Borrow<Q>, Q: Eq + Hash + ?Sized,

Returns the value corresponding to the key in the map.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();

map.insert(1, "a");
map.insert(2, "b");
map.insert(2, "c");
map.insert(3, "d");

assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), Some(&"c"));

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pub fn get_mut<Q>(&mut self, k: &Q) -> Option<&mut V>
where K: Borrow<Q>, Q: Eq + Hash + ?Sized,

Returns the mutable reference corresponding to the key in the map.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();

map.insert(1, "a");
map.insert(2, "b");

*map.get_mut(&1).unwrap() = "c";
assert_eq!(map.get(&1), Some(&"c"));

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pub fn get_refresh<Q>(&mut self, k: &Q) -> Option<&mut V>
where K: Borrow<Q>, Q: Eq + Hash + ?Sized,

Returns the value corresponding to the key in the map.

If value is found, it is moved to the end of the list. This operation can be used in implemenation of LRU cache.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();

map.insert(1, "a");
map.insert(2, "b");
map.insert(3, "d");

assert_eq!(map.get_refresh(&2), Some(&mut "b"));

assert_eq!((&2, &"b"), map.iter().rev().next().unwrap());

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pub fn remove<Q>(&mut self, k: &Q) -> Option<V>
where K: Borrow<Q>, Q: Eq + Hash + ?Sized,

Removes and returns the value corresponding to the key from the map.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();

map.insert(2, "a");

assert_eq!(map.remove(&1), None);
assert_eq!(map.remove(&2), Some("a"));
assert_eq!(map.remove(&2), None);
assert_eq!(map.len(), 0);

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pub fn capacity(&self) -> usize

Returns the maximum number of key-value pairs the map can hold without reallocating.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map: LinkedHashMap<i32, &str> = LinkedHashMap::new();
let capacity = map.capacity();

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pub fn pop_front(&mut self) -> Option<(K, V)>

Removes the first entry.

Can be used in implementation of LRU cache.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();
map.insert(1, 10);
map.insert(2, 20);
map.pop_front();
assert_eq!(map.get(&1), None);
assert_eq!(map.get(&2), Some(&20));

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pub fn front(&self) -> Option<(&K, &V)>

Gets the first entry.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();
map.insert(1, 10);
map.insert(2, 20);
assert_eq!(map.front(), Some((&1, &10)));

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pub fn pop_back(&mut self) -> Option<(K, V)>

Removes the last entry.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();
map.insert(1, 10);
map.insert(2, 20);
map.pop_back();
assert_eq!(map.get(&1), Some(&10));
assert_eq!(map.get(&2), None);

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pub fn back(&self) -> Option<(&K, &V)>

Gets the last entry.

§Examples

use linked_hash_map::LinkedHashMap;
let mut map = LinkedHashMap::new();
map.insert(1, 10);
map.insert(2, 20);
assert_eq!(map.back(), Some((&2, &20)));

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pub fn len(&self) -> usize

Returns the number of key-value pairs in the map.

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pub fn is_empty(&self) -> bool

Returns whether the map is currently empty.

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pub fn hasher(&self) -> &S

Returns a reference to the map’s hasher.

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pub fn clear(&mut self)

Clears the map of all key-value pairs.

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pub fn iter(&self) -> Iter<'_, K, V> ⓘ

Returns a double-ended iterator visiting all key-value pairs in order of insertion. Iterator element type is (&'a K, &'a V)

§Examples

use linked_hash_map::LinkedHashMap;

let mut map = LinkedHashMap::new();
map.insert("a", 10);
map.insert("c", 30);
map.insert("b", 20);

let mut iter = map.iter();
assert_eq!((&"a", &10), iter.next().unwrap());
assert_eq!((&"c", &30), iter.next().unwrap());
assert_eq!((&"b", &20), iter.next().unwrap());
assert_eq!(None, iter.next());

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pub fn iter_mut(&mut self) -> IterMut<'_, K, V> ⓘ

Returns a double-ended iterator visiting all key-value pairs in order of insertion. Iterator element type is (&'a K, &'a mut V)

§Examples

use linked_hash_map::LinkedHashMap;

let mut map = LinkedHashMap::new();
map.insert("a", 10);
map.insert("c", 30);
map.insert("b", 20);

{
    let mut iter = map.iter_mut();
    let mut entry = iter.next().unwrap();
    assert_eq!(&"a", entry.0);
    *entry.1 = 17;
}

assert_eq!(&17, map.get(&"a").unwrap());

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pub fn drain(&mut self) -> Drain<'_, K, V> ⓘ

Clears the map, returning all key-value pairs as an iterator. Keeps the allocated memory for reuse.

If the returned iterator is dropped before being fully consumed, it drops the remaining key-value pairs. The returned iterator keeps a mutable borrow on the vector to optimize its implementation.

Current performance implications (why to use this over into_iter()):

Clears the inner HashMap instead of dropping it
Puts all drained nodes in the free-list instead of deallocating them
Avoids deallocating the sentinel node

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pub fn keys(&self) -> Keys<'_, K, V> ⓘ

Returns a double-ended iterator visiting all key in order of insertion.

§Examples

use linked_hash_map::LinkedHashMap;

let mut map = LinkedHashMap::new();
map.insert('a', 10);
map.insert('c', 30);
map.insert('b', 20);

let mut keys = map.keys();
assert_eq!(&'a', keys.next().unwrap());
assert_eq!(&'c', keys.next().unwrap());
assert_eq!(&'b', keys.next().unwrap());
assert_eq!(None, keys.next());

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pub fn values(&self) -> Values<'_, K, V> ⓘ

Returns a double-ended iterator visiting all values in order of insertion.

§Examples

use linked_hash_map::LinkedHashMap;

let mut map = LinkedHashMap::new();
map.insert('a', 10);
map.insert('c', 30);
map.insert('b', 20);

let mut values = map.values();
assert_eq!(&10, values.next().unwrap());
assert_eq!(&30, values.next().unwrap());
assert_eq!(&20, values.next().unwrap());
assert_eq!(None, values.next());