Memoize function in typescript

cyremur · 2023-07-05T13:57:16.315Z

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?

N

Neto•7/5/23, 2:19 PM

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;
  }
}

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;
  }
}

N

Neto•7/5/23, 2:19 PM

something like this?

N

Neto•7/5/23, 2:19 PM

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");

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");

N

Neto•7/5/23, 2:48 PM

C

cyremurOP•7/5/23, 3:55 PM

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!

N

Neto•7/5/23, 4:00 PM

you can create a context

N

Neto•7/5/23, 4:00 PM

the map would be at the context root

N

Neto•7/5/23, 4:00 PM

no need to "use a class for that"

T

Tom•7/5/23, 4:17 PM

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

N

Neto•7/5/23, 4:26 PM

heavy calculations, such as some pi digit or factorial

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

F

Fagner•7/5/23, 4:29 PM

(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

T

Tom•7/5/23, 4:30 PM

Oh so memorizing the results?

T

Tom•7/5/23, 4:31 PM

Not the function itself?

F

Fagner•7/5/23, 4:31 PM

Yes

F

Fagner•7/5/23, 4:31 PM

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

T

Tom•7/5/23, 4:31 PM

Ok. That makes more sense. Never mind

F

Fagner•7/5/23, 4:31 PM

:)

C

cyremurOP•7/5/23, 8:18 PM

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

C

cyremurOP•7/5/23, 8:18 PM

just trying to find the most elegant approach for that

C

cyremurOP•7/5/23, 8:19 PM

also, my phone error corrected memoize to memorize in the title -.-

C

cyremurOP•7/5/23, 8:35 PM

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;
};

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;
};

N

Neto•7/5/23, 8:36 PM

i mean, if it works

N

Neto•7/5/23, 8:36 PM

its fine

C

cyremurOP•7/5/23, 8:37 PM

yeah lgtm
thanks for the advice

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