TypeScript: Is it possible to get the return type of a generic function?

Question

I have exported a function from some module that looks like:

export function MyFunc() {
    return {
        foo: (in: A) => void
    }
}
         


        

Answer 1

Expanding on Aidin's answer, I've managed to make ReplaceTypeIn, which works for any number of elements, objects as well as arrays, and uses only a couple of lines:

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Derived from https://stackoverflow.com/a/53808212 by jcalz (https://stackoverflow.com/users/2887218)
export type IfEquals =
    (() => G extends T ? 1 : 2) extends
    (() => G extends U ? 1 : 2) ? Y : N;

type ReplaceType = IfEquals;
type ReplaceTypeIn = {
  [K in keyof T]: ReplaceType;
};

// ~~~~~~~~~~~~~~~~~~~~~~ SAMPLE FUNCTIONS ~~~~~~~~~~~~~~~~~~~

export function MyFunc1() {
  return {
    foo: (os: T) => {}
  }
}

function MyFunc2(r: 55, p: T, x: boolean): T {
    return p;
}

// ~~~~~~~~~~~~~~~~~~~~~ FIXATIONS ~~~~~~~~~~~~~~~~~~~~

// Derived from https://stackoverflow.com/a/52964723 by Titian (https://stackoverflow.com/users/125734)
class Helper1  {
    Fixate = (...args: ReplaceTypeIn, unknown, T>) => MyFunc1(...args);
}
type FixatedFunc1 = Helper1['Fixate'];

// -- Usage

type ForNumber1 = FixatedFunc1 //  {foo: (os: number) => void;}
type ForString1 = FixatedFunc1 //  {foo: (os: string) => void;}

// ~~~~~~~~~~~~~~~~~~~

class Helper2  {
    Fixate = (...args: ReplaceTypeIn, unknown, T>) => MyFunc2(...args);
}
type FixatedFunc2 = Helper2['Fixate'];

// -- Usage

type ForNumber2 = FixatedFunc2 //  (r: 55, p: number, x: boolean) => number
type ForString2 = FixatedFunc2 //  (r: 55, p: string, x: boolean) => string

Here's a playground link for the example above.