memo

Memoization tools, TC39 proposal-function-memo implementation.

Entrypoint

This project provides ponyfill and polyfill.

Polyfill has a side effect, so its endpoints are isolated.

The entrypoint of each are as follows:

Type	Entrypoint
Ponyfill	`mod.ts`
Polyfill	`polyfill.ts`

Memoize

memo would create a new function that calls the original function at most once for each tuple of given arguments.

import { memo } from "https://deno.land/x/memoization@$VERSION/mod.ts";

function f(x: number): number {
  console.log(x);
  return x * 2;
}

const fMemo = memo(f);
fMemo(3); // Prints 3 and returns 6.
fMemo(3); // Does not print anything. Returns 6.
fMemo(2); // Prints 2 and returns 4.
fMemo(2); // Does not print anything. Returns 4.
fMemo(3); // Does not print anything. Returns 6.

Either version would work with recursive functions:

import { memo } from "https://deno.land/x/memoization@$VERSION/mod.ts";

const fib = memo((num: number): number => {
  if (num < 2) return num;

  return fib(num - 1) + fib(num - 2);
});

fib(1000);

Custom cache

To control the cache, specify cache.

The cache must implement the following interfaces:

interface MapLike<K, V> {
  get(key: K): V | undefined;

  has(key: K): boolean;

  set(key: K, value: V): void;
}

By default, an unlimited cache is used by WeakMap.

import {
  type MapLike,
  memo,
} from "https://deno.land/x/memoization@$VERSION/mod.ts";

declare const lruCache: MapLike<object, unknown>;
declare const fn: () => void;

const $fn = memo(fn, lruCache);

Keying

Cache keys are function references, new.target, and arguments represented by composite keys.

The equivalence of composite key is the Same-value-zero algorithm. By default, all arguments are used for the cache key.

Specify keys to change the representation of arguments used for cache keys.

import {
  type MapLike,
  memo,
} from "https://deno.land/x/memoization@$VERSION/mod.ts";

declare const respond: (request: Request) => Response;

const $respond = memo(
  respond,
  undefined,
  ([request]) => [request.method, request.url],
);

Polyfill

Polyfill affects the global object. You must be very careful when using it.

import "https://deno.land/x/memoization@$VERSION/polyfill.ts";

const fib = ((num: number): number => {
  if (num < 2) return num;

  return fib(num - 1) + fib(num - 2);
}).memo();

fib(1000);

License

Released under the MIT license