TypeScript Discriminated Union of ReturnTypes

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TypeScript Discriminated Union of ReturnTypes

// DiscriminatedUnionOfReturnTypes.d.ts
type DiscriminatedUnionOfReturnTypes<T> =
  T[keyof T] extends (...args: any[]) => any ? ReturnType<T[keyof T]> : never;

// actionCreators.ts
import * as constants from './constants';

export const actionRequested = () => ({
  type: constants.ACTION_REQUESTED
}) as const;

export const actionRequestFailed = () => ({
  type: constants.ACTION_REQUEST_FAILED
}) as const;

// reducer.ts
import * as actionCreators from './actionCreators'

type Action = DiscriminatedUnionOfReturnTypes<typeof actionCreators>;

// type Action =
//   | { readonly type: 'ACTION_REQUESTED' }
//   | { readonly type: 'ACTION_REQUEST_FAILED' };

DiscriminatedUnionOfReturnTypes.d.ts

/* eslint-disable @typescript-eslint/no-explicit-any */

type DiscriminatedUnionOfReturnTypes<T> =
  T[keyof T] extends (...args: any[]) => any ? ReturnType<T[keyof T]> : never;