💙 returns a different type depending on the value of a function's argument

typed-getter.ts

type Users = any;
type Timetables = any;

type AllTheTypes =
  | { name: 'users'; type: Users }
  | { name: 'timetables'; type: Timetables }

type GetType<A, T> = A extends { name: T } ? A : never


class MyClass {
  public async get<T extends AllTheTypes['name']>(name: T): Promise<GetType<AllTheTypes, T>['type']> {

    return /* something based on `name` */

  }

  public async set<T extends AllTheTypes['name']>(name: T, id: string, data: GetType<AllTheTypes, T>['type']): Promise<void> {
    
    /* do stuff with `name` and `data` */

  }
};


const oof = new MyClass();

oof.get('users').then((data) => {
    // data is is typeof `Users`
});

oof.get('timetable').then((data) => {
    // data is is typeof `Timetables`
});