Inferring function return type then use it instead of function itself

[pocesar]

Not sure if this is already possible with Typescript or it's being discussed (I can't even think about the keywords for the search).

Suppose I have a type defines a function that returns a generic:

    type Function1<T1, R> = (t1: T1) => R;
    interface SomeWrapper<T>{ 
        index: T;
    }

I then accept it as a parameter in a function, inferring it's return value:

    export function funct<P, A1>(
        type: string,
        cb: Function1<A1, P>
    ): Function1<A1, SomeWrapper<P>>;

when funct is called, it then returns a new 'partial' function that returns a wrapped object:

const f1 = funct('string', (param1: string) => ({ param1 }))
// returns a function that when that f1('') => { index: { param1: '' } }, of type Function1

I want to pass this f1 variable to another function, and it'll know the parameter type by inferring it (again):

   export function useFunct<V, A1, F extends Function1<A1, V>>(type: F, reduce: (current: F) => V): V; 

then when doing:

useFunct(f1, (param) => {
  // expect param to be of type string inferred from f1
  // it's of course a function, and not the value of the function
  return {
    param
  }
})

is it possible or it needs an implementation? if not, I think it would be like returnOf keyword (like keyof)

   export function useFunct<V, A1, F extends Function1<A1, V>>(type: F, reduce: (current: returnOf F) => V): V; 

[mhegazy]

Possibly a duplicate of #10247

[pocesar]

well I'm most interested in using the return value of the function, the function parameters can be already be inferred (with the interface and multiple arguments generics), it's a simpler case I think, an extra keyword, not HKTs, like typeof works on plain function definitions, and you get it's "type" so you can put it on an interface

EDIT: now that I'm writing this, I remembered I wrote about something like this in #12497, getting the result of the constructor is the same goal, so it would make things really easy for typed constructors / factories as well

[mhegazy]

#6606 tracks getting the return type of a function/constructor.