Theo's Typesafe Cult•12mo ago

Memoize function in typescript

I want to memoize a pure function in ts that's just a static export without class. Typescript-memoize seems to need a class for the decorator to work. Do I have to wrap my functions into a class and possibly use a singleton or is there a simpler way to pull off memoization?

14 Replies

Neto•12mo ago

class Memo {
  private map = new Map<unknown, unknown>();

  memoize<T extends (...args: any[]) => any>(fn: T): T {
    return ((...args: any[]) => {
      const key = JSON.stringify([fn.toString(), args].join("__"));
      if (this.map.has(key)) {
        console.log("cache hit", key);
        return this.map.get(key);
      }
      const result = fn(...args);
      console.log("cache miss", key);
      this.map.set(key, result);
      return result;
    }) as T;
  }
}

class Memo {
  private map = new Map<unknown, unknown>();

  memoize<T extends (...args: any[]) => any>(fn: T): T {
    return ((...args: any[]) => {
      const key = JSON.stringify([fn.toString(), args].join("__"));
      if (this.map.has(key)) {
        console.log("cache hit", key);
        return this.map.get(key);
      }
      const result = fn(...args);
      console.log("cache miss", key);
      this.map.set(key, result);
      return result;
    }) as T;
  }
}

something like this?

const memo = new Memo();

memo.memoize((a: number, b: number) => a + b)(1, 2);
memo.memoize((a: number, b: number) => a + b)(1, 2);
memo.memoize((c: number, d: number) => c + d)(1, 2);
memo.memoize((a: number, b: number) => a + b)(1, 3);
memo.memoize((a: number, b: number) => a + b)(1, 2);
memo.memoize((c: string, d: string) => [c + d].join("__"))("a", "b");
memo.memoize((c: string, d: string) => [c + d].join("__"))("a", "b");

const memo = new Memo();

memo.memoize((a: number, b: number) => a + b)(1, 2);
memo.memoize((a: number, b: number) => a + b)(1, 2);
memo.memoize((c: number, d: number) => c + d)(1, 2);
memo.memoize((a: number, b: number) => a + b)(1, 3);
memo.memoize((a: number, b: number) => a + b)(1, 2);
memo.memoize((c: string, d: string) => [c + d].join("__"))("a", "b");
memo.memoize((c: string, d: string) => [c + d].join("__"))("a", "b");

Neto•12mo ago

cyremur•12mo ago

yeah I think the part I'm uncertain about is it being a class and where to save the instance and map in my t3 app but I think I'll go with something like that thanks!

Neto•12mo ago

you can create a context the map would be at the context root no need to "use a class for that"

Tom•12mo ago

wait. im just confused. why would you need to memoize a pure function?

Neto•12mo ago

heavy calculations, such as some pi digit or factorial

Fagner•12mo ago

(I think) the goal is to not execute the function again and again, so the result is always the same since the input is the same

Tom•12mo ago

Oh so memorizing the results? Not the function itself?

Fagner•12mo ago

Yes I mean, that's what I think. instead of calling the function it'll check for the memoized data and return the output instead

Tom•12mo ago

Ok. That makes more sense. Never mind

Fagner•12mo ago

cyremur•12mo ago

for context: it's a pathfinding algorithm on a gameboard and I wouldn't want it to run on every render, so atm my approach is to save the result until a player makes another move just trying to find the most elegant approach for that also, my phone error corrected memoize to memorize in the title -.- So I ended up just throwing this into a .ts file. Is it bad practice to just use globals for this kinda stuff or is it really that simple? Seems to work fine for me... @nyx (Rustular DevRel)

let lastNumActions = 0;
let lastPathsDict = {};

export const getBestAvailablePathsDict = (game: GameState) => {
  if (game.combatLog.length === lastNumActions) {
    return lastPathsDict;
  }
  //
  // lots of calculations
  //
  lastNumActions = game.combatLog.length;
  lastPathsDict = pathsDict;
  return pathsDict;
};

let lastNumActions = 0;
let lastPathsDict = {};

export const getBestAvailablePathsDict = (game: GameState) => {
  if (game.combatLog.length === lastNumActions) {
    return lastPathsDict;
  }
  //
  // lots of calculations
  //
  lastNumActions = game.combatLog.length;
  lastPathsDict = pathsDict;
  return pathsDict;
};

Neto•12mo ago

i mean, if it works its fine

cyremur•12mo ago

yeah lgtm thanks for the advice

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Memoize function in typescript