Higher order type inference from generic functions lost when result type is wrapped

[maclockard]

Bug Report

🔎 Search Terms

Higher order type, Higher kinded type, Inference generic lost, Wrapped

🕗 Version & Regression Information

and fill in the line that best applies:

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about higher order type inference

⏯ Playground Link

Playground link with relevant code

💻 Code

declare function wrapFuncResult<A extends any[], R>(func: (...args: A) => R): (...args: A) => { wrapped: R };

declare function wrapFuncResult2<A extends any[], R>(func: (...args: A) => R): { wrappedFunc: (...args: A) => { inner: R } };

declare const stringToNum: (s: string) => number;
const stringToNumWrapped = wrapFuncResult(stringToNum); // (s: string) => { wrapped: number }
const stringToNumWrapped2 = wrapFuncResult2(stringToNum); // { wrappedFunc: (s: string) => { wrapped: number } }

declare const toArray: <T>(t: T) => T[];
const toArrayWrapped = wrapFuncResult(toArray);  // <T>(t: T) => { wrapped: T[] }
const toArrayWrapped2 = wrapFuncResult2(toArray); // { wrappedFunc: (t: any) => { wrapped: any[] } } - :(

🙁 Actual behavior

The function toArrayWrapped2 is of type { wrappedFunc: (t: any) => { wrapped: any[] } }. The inference of the type parameter T from toArray was lost when the return type was wrapped.

🙂 Expected behavior

The function toArrayWrapped2 is of type { wrappedFunc: <T>(t: T) => { wrapped: T[] } }. This would preserve the type parameter T from toArray just like the unwrapped result type of toArrayWrapped.

[jcalz]

Duplicate of (or strongly related to) #49505

[typescript-bot]

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