#memoization #memo #lazy-evaluation #cache #derive-debug

no-std core_memo

Zero-cost, no_std-compatible library for lazy evaluation and memoization

1 unstable release

Uses old Rust 2015

0.1.0 Jun 15, 2018

#269 in Caching


288 lines

Simple Memoization Library

core_memo is a simple, straightforward, zero-cost Rust library for lazy evaluation and memoization. It does not do memory allocations or dynamic dispatch and it is #![no_std]-compatible. It has no dependencies.

See the docs for more info!


use core_memo::{Memoize, Memo, MemoExt};

#[derive(Debug, PartialEq, Eq)] // for assert_eq! later
struct MemoSum(i32);

impl Memoize for MemoSum {
    type Param = [i32];

    fn memoize(p: &[i32]) -> MemoSum {

// The `Memo` type holds ownership over the parameter for the calculation
// There are also the `MemoExt` and `MemoOnce` types with different semantics

let mut memo: Memo<MemoSum, _> = Memo::new(vec![1, 2]);

// Our `memoize` method is called the first time we call `memo.get()`
assert_eq!(memo.get(), &MemoSum(3));

// Further calls to `memo.get()` return the cached value without reevaluating
assert_eq!(memo.get(), &MemoSum(3));

// We can mutate the parameter held inside the `Memo`:

// via a mutable reference
// via a closure
memo.update_param(|p| p.push(4));

// either way, the `Memo` forgets any cached value and it will be
// reevaluated on the next call to `memo.get()`

assert_eq!(memo.get(), &MemoSum(10)); // the vec is now `[1, 2, 3, 4]`

No runtime deps