rust 37 lines · 6 steps

A generic memoizer in Rust

A reusable struct that caches the results of any pure function, keyed by its input.

Explained by highlit
Intermediate memoization generics caching closures trait-bounds
1use std::collections::HashMap;
2 
3pub struct Memoizer<K, V, F> {
4 cache: HashMap<K, V>,
5 compute: F,
6}
7 
8impl<K, V, F> Memoizer<K, V, F>
9where
10 K: std::hash::Hash + Eq + Clone,
11 V: Clone,
12 F: Fn(&K) -> V,
13{
14 pub fn new(compute: F) -> Self {
15 Self {
16 cache: HashMap::new(),
17 compute,
18 }
19 }
20 
21 pub fn get(&mut self, key: K) -> V {
22 if let Some(value) = self.cache.get(&key) {
23 return value.clone();
24 }
25 let value = (self.compute)(&key);
26 self.cache.insert(key, value.clone());
27 value
28 }
29 
30 pub fn len(&self) -> usize {
31 self.cache.len()
32 }
33 
34 pub fn invalidate(&mut self, key: &K) -> Option<V> {
35 self.cache.remove(key)
36 }
37}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Storing a closure in a generic field lets one struct memoize any compatible function.
  2. 2Trait bounds like Hash, Eq, and Clone express exactly what the cache needs from its types.
  3. 3Checking the cache before computing turns repeated work into a single hash lookup.

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