Update ReadonlyArray.ts

[christiantakle]

Fix: #1929

Not sure about adding a test here since the size of the input depend on nodejs and/or the machine its running on.

Example using the change

Note the source code is inline so its simpler to play with.

/** Inlined from source code */
const isEmpty = <A>(as: ReadonlyArray<A>): as is readonly [] => as.length === 0;
// const empty: ReadonlyArray<never> = RNEA.empty
const empty: ReadonlyArray<never> = [];

const value = {};
// const a: Array<Array<typeof value>> = [new Array(112201).fill(value)];
/**
 * 112201, the number that failed in production and on an Apple M1 Max 64gb.
 * I had to increase the number to see a similar failure on my desktop workstation hence the
 * `* 2`
 */
const ass: Array<Array<typeof value>> = [new Array(112201 * 2).fill(value)];

// chainWithIndex from ReadonlyArray
const chainWithIndex =
  <A, B>(f: (i: number, a: A) => ReadonlyArray<B>) =>
  (as: ReadonlyArray<A>): ReadonlyArray<B> => {
    if (isEmpty(as)) {
      return empty;
    }
    const out: Array<B> = [];
    for (let i = 0; i < as.length; i++) {
      out.push(...f(i, as[i]));
    }
    return out;
  };

// Alternative implementation
export const chainWithIndex2 =
  <A, B>(f: (i: number, a: A) => ReadonlyArray<B>) =>
  (as: ReadonlyArray<A>): ReadonlyArray<B> => {
    if (isEmpty(as)) {
      return [];
    }
    const out: Array<B> = [];
    for (let i = 0; i < as.length; i++) {
      const bs = f(i, as[i]);
      for (let j = 0; j < bs.length; j++) {
        out.push(bs[j]);
      }
    }
    return out;
  };

const main = () => {
  console.log({ assLength: ass.length });

  {
    console.log("original start");
    try {
      const as = chainWithIndex((_, x) => x)(ass);
      console.log({ asLength: as.length });
    } catch (err: any) {
      console.log("[original][catch]", err.message);
    }
    console.log("original end");
  }

  {
    console.log("alternative start");
    const as = chainWithIndex2((_, x) => x)(ass);
    console.log({ asLength: as.length });
    console.log("alternative end");
  }
  console.log("done");
};

main();

Command used to run it:

ts-node --transpile-only x.ts

Output:

{ assLength: 1 }
original start
[original][catch] Maximum call stack size exceeded
original end
alternative start
{ asLength: 224402 }
alternative end
done

[gcanti]

Thanks @christiantakle

The issue lies with the use of Array.push in conjunction with the spread operator. There are three other instances of this problem. You can locate them by searching for ".push(...". Could you please address these occurrences as well?

[christiantakle]

@gcanti Done.

I do make a change to package-lock.json when running npm install assume its okay to include it here.

[christiantakle]

If you want I can merge the commits for the .push(... change or kill this pr and make a new one with that change just to reduce noise and co-locate import change. I was just being lazy and did the first commit from the github interface.

[christiantakle]

Prefer #1931