Struct lru::LruCache

pub struct LruCache<K, V, S = DefaultHasher> { /* private fields */ }

An LRU Cache

Implementations

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

pub fn new(cap: NonZeroUsize) -> LruCache<K, V>

Creates a new LRU Cache that holds at most cap items.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache: LruCache<isize, &str> = LruCache::new(NonZeroUsize::new(10).unwrap());

pub fn unbounded() -> LruCache<K, V>

Creates a new LRU Cache that never automatically evicts items.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache: LruCache<isize, &str> = LruCache::unbounded();

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

pub fn with_hasher(cap: NonZeroUsize, hash_builder: S) -> LruCache<K, V, S>

Creates a new LRU Cache that holds at most cap items and uses the provided hash builder to hash keys.

Example

use lru::{LruCache, DefaultHasher};
use std::num::NonZeroUsize;

let s = DefaultHasher::default();
let mut cache: LruCache<isize, &str> = LruCache::with_hasher(NonZeroUsize::new(10).unwrap(), s);

pub fn unbounded_with_hasher(hash_builder: S) -> LruCache<K, V, S>

Creates a new LRU Cache that never automatically evicts items and uses the provided hash builder to hash keys.

Example

use lru::{LruCache, DefaultHasher};

let s = DefaultHasher::default();
let mut cache: LruCache<isize, &str> = LruCache::unbounded_with_hasher(s);

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

Puts a key-value pair into cache. If the key already exists in the cache, then it updates the key’s value and returns the old value. Otherwise, None is returned.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

assert_eq!(None, cache.put(1, "a"));
assert_eq!(None, cache.put(2, "b"));
assert_eq!(Some("b"), cache.put(2, "beta"));

assert_eq!(cache.get(&1), Some(&"a"));
assert_eq!(cache.get(&2), Some(&"beta"));

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

Pushes a key-value pair into the cache. If an entry with key k already exists in the cache or another cache entry is removed (due to the lru’s capacity), then it returns the old entry’s key-value pair. Otherwise, returns None.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

assert_eq!(None, cache.push(1, "a"));
assert_eq!(None, cache.push(2, "b"));

// This push call returns (2, "b") because that was previously 2's entry in the cache.
assert_eq!(Some((2, "b")), cache.push(2, "beta"));

// This push call returns (1, "a") because the cache is at capacity and 1's entry was the lru entry.
assert_eq!(Some((1, "a")), cache.push(3, "alpha"));

assert_eq!(cache.get(&1), None);
assert_eq!(cache.get(&2), Some(&"beta"));
assert_eq!(cache.get(&3), Some(&"alpha"));

pub fn get<'a, Q>(&'a mut self, k: &Q) -> Option<&'a V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a reference to the value of the key in the cache or None if it is not present in the cache. Moves the key to the head of the LRU list if it exists.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.put(2, "c");
cache.put(3, "d");

assert_eq!(cache.get(&1), None);
assert_eq!(cache.get(&2), Some(&"c"));
assert_eq!(cache.get(&3), Some(&"d"));

pub fn get_mut<'a, Q>(&'a mut self, k: &Q) -> Option<&'a mut V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a mutable reference to the value of the key in the cache or None if it is not present in the cache. Moves the key to the head of the LRU list if it exists.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put("apple", 8);
cache.put("banana", 4);
cache.put("banana", 6);
cache.put("pear", 2);

assert_eq!(cache.get_mut(&"apple"), None);
assert_eq!(cache.get_mut(&"banana"), Some(&mut 6));
assert_eq!(cache.get_mut(&"pear"), Some(&mut 2));

pub fn get_key_value<'a, Q>(&'a mut self, k: &Q) -> Option<(&'a K, &'a V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a key-value references pair of the key in the cache or None if it is not present in the cache. Moves the key to the head of the LRU list if it exists.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(String::from("1"), "a");
cache.put(String::from("2"), "b");
cache.put(String::from("2"), "c");
cache.put(String::from("3"), "d");

assert_eq!(cache.get_key_value("1"), None);
assert_eq!(cache.get_key_value("2"), Some((&String::from("2"), &"c")));
assert_eq!(cache.get_key_value("3"), Some((&String::from("3"), &"d")));

pub fn get_key_value_mut<'a, Q>( &'a mut self, k: &Q, ) -> Option<(&'a K, &'a mut V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a key-value references pair of the key in the cache or None if it is not present in the cache. The reference to the value of the key is mutable. Moves the key to the head of the LRU list if it exists.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");
let (k, v) = cache.get_key_value_mut(&1).unwrap();
assert_eq!(k, &1);
assert_eq!(v, &mut "a");
*v = "aa";
cache.put(3, "c");
assert_eq!(cache.get_key_value(&2), None);
assert_eq!(cache.get_key_value(&1), Some((&1, &"aa")));
assert_eq!(cache.get_key_value(&3), Some((&3, &"c")));

pub fn get_or_insert<F>(&mut self, k: K, f: F) -> &V

where F: FnOnce() -> V,

Returns a reference to the value of the key in the cache if it is present in the cache and moves the key to the head of the LRU list. If the key does not exist the provided FnOnce is used to populate the list and a reference is returned.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.put(2, "c");
cache.put(3, "d");

assert_eq!(cache.get_or_insert(2, ||"a"), &"c");
assert_eq!(cache.get_or_insert(3, ||"a"), &"d");
assert_eq!(cache.get_or_insert(1, ||"a"), &"a");
assert_eq!(cache.get_or_insert(1, ||"b"), &"a");

pub fn try_get_or_insert<F, E>(&mut self, k: K, f: F) -> Result<&V, E>

where F: FnOnce() -> Result<V, E>,

Returns a reference to the value of the key in the cache if it is present in the cache and moves the key to the head of the LRU list. If the key does not exist the provided FnOnce is used to populate the list and a reference is returned. If FnOnce returns Err, returns the Err.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.put(2, "c");
cache.put(3, "d");

let f = ||->Result<&str, String> {Err("failed".to_owned())};
let a = ||->Result<&str, String> {Ok("a")};
let b = ||->Result<&str, String> {Ok("b")};
assert_eq!(cache.try_get_or_insert(2, a), Ok(&"c"));
assert_eq!(cache.try_get_or_insert(3, a), Ok(&"d"));
assert_eq!(cache.try_get_or_insert(4, f), Err("failed".to_owned()));
assert_eq!(cache.try_get_or_insert(5, b), Ok(&"b"));
assert_eq!(cache.try_get_or_insert(5, a), Ok(&"b"));

pub fn get_or_insert_mut<F>(&mut self, k: K, f: F) -> &mut V

where F: FnOnce() -> V,

Returns a mutable reference to the value of the key in the cache if it is present in the cache and moves the key to the head of the LRU list. If the key does not exist the provided FnOnce is used to populate the list and a mutable reference is returned.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");

let v = cache.get_or_insert_mut(2, ||"c");
assert_eq!(v, &"b");
*v = "d";
assert_eq!(cache.get_or_insert_mut(2, ||"e"), &mut "d");
assert_eq!(cache.get_or_insert_mut(3, ||"f"), &mut "f");
assert_eq!(cache.get_or_insert_mut(3, ||"e"), &mut "f");

pub fn try_get_or_insert_mut<F, E>(&mut self, k: K, f: F) -> Result<&mut V, E>

where F: FnOnce() -> Result<V, E>,

Returns a mutable reference to the value of the key in the cache if it is present in the cache and moves the key to the head of the LRU list. If the key does not exist the provided FnOnce is used to populate the list and a mutable reference is returned. If FnOnce returns Err, returns the Err.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.put(2, "c");

let f = ||->Result<&str, String> {Err("failed".to_owned())};
let a = ||->Result<&str, String> {Ok("a")};
let b = ||->Result<&str, String> {Ok("b")};
if let Ok(v) = cache.try_get_or_insert_mut(2, a) {
    *v = "d";
}
assert_eq!(cache.try_get_or_insert_mut(2, a), Ok(&mut "d"));
assert_eq!(cache.try_get_or_insert_mut(3, f), Err("failed".to_owned()));
assert_eq!(cache.try_get_or_insert_mut(4, b), Ok(&mut "b"));
assert_eq!(cache.try_get_or_insert_mut(4, a), Ok(&mut "b"));

pub fn peek<'a, Q>(&'a self, k: &Q) -> Option<&'a V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a reference to the value corresponding to the key in the cache or None if it is not present in the cache. Unlike get, peek does not update the LRU list so the key’s position will be unchanged.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");

assert_eq!(cache.peek(&1), Some(&"a"));
assert_eq!(cache.peek(&2), Some(&"b"));

pub fn peek_mut<'a, Q>(&'a mut self, k: &Q) -> Option<&'a mut V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a mutable reference to the value corresponding to the key in the cache or None if it is not present in the cache. Unlike get_mut, peek_mut does not update the LRU list so the key’s position will be unchanged.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");

assert_eq!(cache.peek_mut(&1), Some(&mut "a"));
assert_eq!(cache.peek_mut(&2), Some(&mut "b"));

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

Returns the value corresponding to the least recently used item or None if the cache is empty. Like peek, peek_lru does not update the LRU list so the item’s position will be unchanged.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");

assert_eq!(cache.peek_lru(), Some((&1, &"a")));

pub fn contains<Q>(&self, k: &Q) -> bool

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a bool indicating whether the given key is in the cache. Does not update the LRU list.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.put(3, "c");

assert!(!cache.contains(&1));
assert!(cache.contains(&2));
assert!(cache.contains(&3));

pub fn pop<Q>(&mut self, k: &Q) -> Option<V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Removes and returns the value corresponding to the key from the cache or None if it does not exist.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(2, "a");

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

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

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Removes and returns the key and the value corresponding to the key from the cache or None if it does not exist.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "a");

assert_eq!(cache.pop(&1), Some("a"));
assert_eq!(cache.pop_entry(&2), Some((2, "a")));
assert_eq!(cache.pop(&1), None);
assert_eq!(cache.pop_entry(&2), None);
assert_eq!(cache.len(), 0);

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

Removes and returns the key and value corresponding to the least recently used item or None if the cache is empty.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(2, "a");
cache.put(3, "b");
cache.put(4, "c");
cache.get(&3);

assert_eq!(cache.pop_lru(), Some((4, "c")));
assert_eq!(cache.pop_lru(), Some((3, "b")));
assert_eq!(cache.pop_lru(), None);
assert_eq!(cache.len(), 0);

pub fn promote<Q>(&mut self, k: &Q)

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Marks the key as the most recently used one.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(3).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.put(3, "c");
cache.get(&1);
cache.get(&2);

// If we do `pop_lru` now, we would pop 3.
// assert_eq!(cache.pop_lru(), Some((3, "c")));

// By promoting 3, we make sure it isn't popped.
cache.promote(&3);
assert_eq!(cache.pop_lru(), Some((1, "a")));

pub fn demote<Q>(&mut self, k: &Q)

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Marks the key as the least recently used one.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(3).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.put(3, "c");
cache.get(&1);
cache.get(&2);

// If we do `pop_lru` now, we would pop 3.
// assert_eq!(cache.pop_lru(), Some((3, "c")));

// By demoting 1 and 2, we make sure those are popped first.
cache.demote(&2);
cache.demote(&1);
assert_eq!(cache.pop_lru(), Some((1, "a")));
assert_eq!(cache.pop_lru(), Some((2, "b")));

pub fn len(&self) -> usize

Returns the number of key-value pairs that are currently in the the cache.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());
assert_eq!(cache.len(), 0);

cache.put(1, "a");
assert_eq!(cache.len(), 1);

cache.put(2, "b");
assert_eq!(cache.len(), 2);

cache.put(3, "c");
assert_eq!(cache.len(), 2);

pub fn is_empty(&self) -> bool

Returns a bool indicating whether the cache is empty or not.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());
assert!(cache.is_empty());

cache.put(1, "a");
assert!(!cache.is_empty());

pub fn cap(&self) -> NonZeroUsize

Returns the maximum number of key-value pairs the cache can hold.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache: LruCache<isize, &str> = LruCache::new(NonZeroUsize::new(2).unwrap());
assert_eq!(cache.cap().get(), 2);

pub fn resize(&mut self, cap: NonZeroUsize)

Resizes the cache. If the new capacity is smaller than the size of the current cache any entries past the new capacity are discarded.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache: LruCache<isize, &str> = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.put(1, "a");
cache.put(2, "b");
cache.resize(NonZeroUsize::new(4).unwrap());
cache.put(3, "c");
cache.put(4, "d");

assert_eq!(cache.len(), 4);
assert_eq!(cache.get(&1), Some(&"a"));
assert_eq!(cache.get(&2), Some(&"b"));
assert_eq!(cache.get(&3), Some(&"c"));
assert_eq!(cache.get(&4), Some(&"d"));

pub fn clear(&mut self)

Clears the contents of the cache.

Example

use lru::LruCache;
use std::num::NonZeroUsize;
let mut cache: LruCache<isize, &str> = LruCache::new(NonZeroUsize::new(2).unwrap());
assert_eq!(cache.len(), 0);

cache.put(1, "a");
assert_eq!(cache.len(), 1);

cache.put(2, "b");
assert_eq!(cache.len(), 2);

cache.clear();
assert_eq!(cache.len(), 0);

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

An iterator visiting all entries in most-recently used order. The iterator element type is (&K, &V).

Examples

use lru::LruCache;
use std::num::NonZeroUsize;

let mut cache = LruCache::new(NonZeroUsize::new(3).unwrap());
cache.put("a", 1);
cache.put("b", 2);
cache.put("c", 3);

for (key, val) in cache.iter() {
    println!("key: {} val: {}", key, val);
}

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

An iterator visiting all entries in most-recently-used order, giving a mutable reference on V. The iterator element type is (&K, &mut V).

Examples

use lru::LruCache;
use std::num::NonZeroUsize;

struct HddBlock {
    dirty: bool,
    data: [u8; 512]
}

let mut cache = LruCache::new(NonZeroUsize::new(3).unwrap());
cache.put(0, HddBlock { dirty: false, data: [0x00; 512]});
cache.put(1, HddBlock { dirty: true,  data: [0x55; 512]});
cache.put(2, HddBlock { dirty: true,  data: [0x77; 512]});

// write dirty blocks to disk.
for (block_id, block) in cache.iter_mut() {
    if block.dirty {
        // write block to disk
        block.dirty = false
    }
}

Trait Implementations

impl<K, V> Clone for LruCache<K, V>

where K: Hash + PartialEq + Eq + Clone, V: Clone,

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<K: Hash + Eq, V, S: BuildHasher> Debug for LruCache<K, V, S>

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

Formats the value using the given formatter.

impl<K, V, S> Drop for LruCache<K, V, S>

fn drop(&mut self)

Executes the destructor for this type.

impl<'a, K: Hash + Eq, V, S: BuildHasher> IntoIterator for &'a LruCache<K, V, S>

type Item = (&'a K, &'a V)

The type of the elements being iterated over.

type IntoIter = Iter<'a, K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Iter<'a, K, V>

Creates an iterator from a value.

impl<'a, K: Hash + Eq, V, S: BuildHasher> IntoIterator for &'a mut LruCache<K, V, S>

type Item = (&'a K, &'a mut V)

The type of the elements being iterated over.

type IntoIter = IterMut<'a, K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> IterMut<'a, K, V>

Creates an iterator from a value.

impl<K: Hash + Eq, V> IntoIterator for LruCache<K, V>

type Item = (K, V)

The type of the elements being iterated over.

type IntoIter = IntoIter<K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> IntoIter<K, V>

Creates an iterator from a value.

impl<K: Send, V: Send, S: Send> Send for LruCache<K, V, S>

impl<K: Sync, V: Sync, S: Sync> Sync for LruCache<K, V, S>