Method concat has wrong typization

[phpcoder2022]

🔎 Search Terms

typescript, concat, bug

🕗 Version & Regression Information

I tested this behavior on version 5.4.5. Local and playground results are equal.
I attached link to playground for demo.
You can see problem in output array. It isn't contains only arrays, but contains just numbers too.

⏯ Playground Link

https://www.typescriptlang.org/play/?jsx=0#code/C4TwDgpgBAcgrgWwEYQE4GUIEc4QHYDG0AvFHoiqgNoC6A3AFAMED2eAzsFMAIYDWEeMjTsopABQA6ae2y5CEdgC5YFNJhz4itAJRiAfFADeDKFFYcWAGwiSrLAObiABgEE8IKDwLAAlm1EAd19gAAsvVFQeEHZnABooWU0Fdh1GAF9GZgCuHgATPKFKdkxgUQlpSXJhDAgylQAFHiiEOpEAHlBIFgAzbn5BNVR2fV0DY1MyIdL2SR6WVABRb1DxWS5iQ14BIpEpGTqdNIZMpnzCoZK69nEqKgBGBIAmBIBmGhpJCwIeYFuAFgSAFYEgA2GhHOhAA

💻 Code

type NumberSequence = number[];

const takeNumbers = (...sequences: NumberSequence[]) => {
  console.log(`Any actions with arrays`, sequences);
};

const addNumbersSets = (...numberSets: Parameters<typeof takeNumbers>[]) => {
  numberSets.forEach(set => takeNumbers(...set));
};

addNumbersSets([[1, 2, 3]].concat([4, 5, 6]));

🙁 Actual behavior

Output array contains numbers

🙂 Expected behavior

Output array contains only arrays of numbers

Additional information about the issue

No response

[whzx5byb]

Duplicate of #19535.

[phpcoder2022]

How for need generic type ConcatArray<T>? I wrote this type locally:

type ConcatArg<RawType> = RawType extends unknown[] ? RawType[] : (RawType | RawType[]);

interface Array<T> {
  concat(...items: ConcatArg<T>[]): T[];
}

Is it a acceptable solution?

[nmain]

Is it a acceptable solution?

If it works for you, use it! My interpretation of #36554 is that the TypeScript team probably not interested in adopting such a change unless it's part of a holistic revamp of array typing issues, with consideration given to all users and possible breaking changes.

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.