@miyauci/memo
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Memoization tools, TC39 proposal-function-memo implementation
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[](https://deno.land/x/memoization)
[](https://deno.land/x/memoization?doc)
[](https://github.com/TomokiMiyauci/memo/releases)
[](https://codecov.io/gh/TomokiMiyauci/memo)
[](LICENSE)
[](https://github.com/TomokiMiyauci/memo/actions/workflows/test.yaml)
[](https://nodei.co/npm/@miyauci/memo/)
[](https://github.com/RichardLitt/standard-readme)
[](https://github.com/semantic-release/semantic-release)
Memoization tools, TC39
[proposal-function-memo](https://github.com/tc39/proposal-function-memo)
implementation.
## Install
deno.land:
```ts
import * as mod from "https://deno.land/x/memoization@$VERSION/mod.ts";
```
npm:
```bash
npm i @miyauci/memo
```
## Usage
Returns the proxy function whose call is monitored. It calls at most once for
each given arguments.
```ts
import { memo } from "https://deno.land/x/memoization@$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:
```ts
import { memo } from "https://deno.land/x/memoization@$VERSION/mod.ts";
const fib = memo((num: number): number => {
if (num < 2) return num;
return fib(num - 1) + fib(num - 2);
});
fib(1000);
```
To control the cache, specify `cache`.
The cache must implement the following interfaces:
```ts
interface MapLike<K, V> {
get(key: K): V | undefined;
has(key: K): boolean;
set(key: K, value: V): void;
}
```
By default, an unlimited cache is used by `WeakMap`.
```ts
import {
type MapLike,
memo,
} from "https://deno.land/x/memoization@$VERSION/mod.ts";
declare const lruCache: MapLike<object, unknown>;
declare const fn: () => unknown;
const $fn = memo(fn, lruCache);
```
Cache keys are represented by
[](https://github.com/tc39/proposal-richer-keys/tree/master/compositeKey).
The composite keys are passed several elements for the key, called components.
The components are as follows:
- target function
- this arg(`this`)
- new target(`new.target`)
- args
Of these, target function is used to identify a unique function. The target
function is not used to identify a unique function, since the composite key is a
global registry. For more information, see
[FAQ: What scope is the idempotentcy?](https://github.com/tc39/proposal-richer-keys/tree/master/compositeKey#what-scope-is-the-idempotentcy)
Also, composite key employs the
[same-value-zero](https://tc39.es/ecma262/#sec-samevaluezero) algorithm to
verify the equivalence of each component.
You can modify the args component through the `keying` callback.
```ts
import {
type MapLike,
memo,
} from "https://deno.land/x/memoization@$VERSION/mod.ts";
declare const respond: (request: Request) => Response;
const $respond = memo(
respond,
undefined,
([request]) => [request.method, request.url],
);
```
Currently, only the args component can be modified. This is being discussed in
[
and it is not clear how this arg and new target should be handled.
Caching of instantiation is also supported. Calls to constructor functions with
the `new` operator are cacheable based on their arguments.
```ts
import { memo } from "https://deno.land/x/memoization@$VERSION/mod.ts";
import { assert } from "https://deno.land/std/testing/asserts.ts";
assert(new Error() !== new Error());
const $Error = memo(Error);
assert(new $Error() === new $Error());
assert($Error("test") === $Error("test"));
assert(new $Error() !== $Error());
assert(new $Error() !== new $Error("test"));
```
Polyfill affects the global object. You must be very careful when using it.
```ts
import "https://deno.land/x/memoization@$VERSION/polyfill.ts";
const fib = ((num: number): number => {
if (num < 2) return num;
return fib(num - 1) + fib(num - 2);
}).memo();
fib(1000);
```
See [deno doc](https://deno.land/x/memoization?doc) for all APIs.
See [CONTRIBUTING.md](CONTRIBUTING.md)
[](LICENSE) © 2023 Tomoki Miyauchi