Typing the `rubico` library `fork` function

Question

I'm trying to create types for the library rubico, for fun. I'm in problems to do that because of your generality. For example, the function fork:

type GenericFunction<OUT = any> = (...args: readonly any[]) => OUT;

type Dict<T> = { [k: string]: T };

// https://stackoverflow.com/questions/48011353/how-to-unwrap-type-of-a-promise#fromHistory
type Awaited<T> = T extends PromiseLike<infer U> ? Awaited<U> : T;

declare function fork<
  IN extends Dict<GenericFunction>,
  OUT = { [k in keyof IN]: Awaited<ReturnType<IN[k]>> },
  RS = ReturnType<IN[keyof IN]>,
  >(obj: IN): RS extends Promise<any> ? Promise<OUT> : OUT;

const res1: { x: number, y: string } = fork({
  x: (x: number) => x,
  y: (y: string) => y,
});

// This does't works
const res2: Promise<{ x: number, y: number }> = fork({
  x: (x: number) => x,
  y: async (x: number) => x,
});

// This works
const res3: Promise<{ x: number, y: number }> = fork({
  x: async (x: number) => x,
  y: async (x: number) => x,
});

I'm a bit tired to continue thinking about that alone, so if someone can help me, I will thank you very much.

Edit 1

I want to know if it's possible to force the typescript to use Promise ever when any type of the return of the input object is Promise?

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. — Community, Nov 09 '21 at 17:53
Please provide reproducible example. Where did you get `GenericFunction` ? — captain-yossarian from Ukraine, Nov 12 '21 at 12:59
What are restrictions? I assume that if one of the obj properties returns Promise - then whole output should be wrapped in Promise, correct? COuld you please also share the function implementation. It will be easier to understand the constraints — captain-yossarian from Ukraine, Nov 15 '21 at 09:20

Typing the `rubico` library `fork` function

Edit 1

0 Answers0