cache_mod/
cache.rs

1//! The [`Cache`] trait — the common contract every cache type in this crate
2//! implements.
3
4use core::hash::Hash;
5
6/// The common read / write / evict contract every cache type in this crate
7/// implements.
8///
9/// All methods take `&self` (not `&mut self`) so a cache instance can be
10/// shared across threads and across `.await` points without external locking.
11/// Implementations use interior mutability.
12///
13/// # Access semantics
14///
15/// - [`get`](Self::get) is an **access**: it may update the eviction order
16///   (e.g. promoting the entry to most-recently-used).
17/// - [`contains_key`](Self::contains_key) is a **query** only: it must not
18///   update the eviction order.
19/// - [`insert`](Self::insert) is an access on the inserted key.
20/// - [`remove`](Self::remove) is destructive and does not update order.
21///
22/// # Example
23///
24/// ```
25/// use cache_mod::{Cache, LruCache};
26///
27/// let cache: LruCache<&'static str, u32> = LruCache::new(4).expect("capacity > 0");
28///
29/// assert_eq!(cache.insert("a", 1), None);
30/// assert_eq!(cache.get(&"a"), Some(1));
31/// assert!(cache.contains_key(&"a"));
32/// assert_eq!(cache.len(), 1);
33///
34/// assert_eq!(cache.remove(&"a"), Some(1));
35/// assert!(cache.is_empty());
36/// ```
37pub trait Cache<K, V>
38where
39    K: Eq + Hash,
40    V: Clone,
41{
42    /// Returns the value associated with `key`, if any, and counts as an
43    /// access for the purposes of the eviction policy.
44    fn get(&self, key: &K) -> Option<V>;
45
46    /// Inserts `value` under `key`. Returns the previously-stored value if
47    /// `key` was already present.
48    ///
49    /// May evict one or more existing entries to make room, according to
50    /// the cache's eviction policy.
51    fn insert(&self, key: K, value: V) -> Option<V>;
52
53    /// Removes the entry for `key` and returns the value if present.
54    fn remove(&self, key: &K) -> Option<V>;
55
56    /// Returns `true` if the cache currently holds an entry for `key`.
57    ///
58    /// Unlike [`get`](Self::get), this method does **not** count as an
59    /// access — eviction order is left unchanged.
60    fn contains_key(&self, key: &K) -> bool;
61
62    /// Number of entries currently stored.
63    fn len(&self) -> usize;
64
65    /// Returns `true` when the cache holds no entries.
66    fn is_empty(&self) -> bool {
67        self.len() == 0
68    }
69
70    /// Removes every entry. Capacity is preserved.
71    fn clear(&self);
72
73    /// Configured maximum number of entries.
74    fn capacity(&self) -> usize;
75}
cache_mod/cache.rs

cache_mod/
cache.rs
