Better typings for Promise, like #31117 - #33707

    // Promise.all(this.fork) take a T1[] where T1 is a Promise<number>
    // and return a Promise<T2[]> where T2 is a number
    // therefore T1 and T2 are not both «T»

export class MyMaybeList<T = any> {
  private constructor(values: T[]) {
    this.values = values;
  }

  private values: T[];

  // get =======================================================-| fork() |-====

  public get fork(): T[] {
    return this.values != null ? this.values.slice() : [].slice();
  }

  // public =====================================================-| map() |-====

  public map<R = any>(
    fn: (val: T, index: number, array: T[]) => R
  ): MyMaybeList<R> {
    return MyMaybeList.of(...this.values.map(fn));
  }

  // static ======================================================-| of() |-====

  public static of<TVal>(...val: TVal[]): MyMaybeList<TVal> {
    if (val == null || !val.length) return new MyMaybeList<TVal>([]);
    return new MyMaybeList<TVal>([...val]);
  }

  // async =====================================================-| will() |-====

  public async will /* <R> */() /* : Promise<MyMaybeList<R>> */ {
    // Promise.all(this.fork) take a T1[] where T1 is Promise<number>
    // and return a Promise<T2[]> where T2 is a number
    // therefore T1 and T2 are not both «T»
    console.log(this.fork);

    const willThen = Promise.all(this.fork);

    const thenWill = await willThen;
    return MyMaybeList.of(...thenWill);
  }
}

const oneToTen = MyMaybeList.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
const powersOneToTen = oneToTen.map(async val => val * val);

// "log->" powersOneToTen: MyMaybeList<Promise<number>>
console.log(powersOneToTen);

// "log->" awaitedList: MyMaybeList<Promise<number>>
// instead of a -> MyMaybeList { Promise<number> }
// in fact is a -> Promise {  MyMaybeList<number> }
const awaitedPowersOneToTen = powersOneToTen.will /* <unnknow> */();
awaitedPowersOneToTen.then(awaitedList => console.log(awaitedList));

// Promise { <pending> } will resolve into ->
console.log(awaitedPowersOneToTen);

/*
 // Promise.all(this.fork) take a T1[] where T1 is Promise<number>
    // and return a Promise<T2[]> where T2 is a number
    // therefore T1 and T2 are not both «T»
    // console.log(this.fork); will display same as console.log(powersOneToTen);



// console.log(powersOneToTen); ->
// "log->" powersOneToTen: MyMaybeList<Promise<number>>
MyMaybeList {
  values: [
    Promise { 1 },
    Promise { 4 },
    Promise { 9 },
    Promise { 16 },
    Promise { 25 },
    Promise { 36 },
    Promise { 49 },
    Promise { 64 },
    Promise { 81 },
    Promise { 100 }
  ]
}



// console.log(awaitedPowersOneToTen); ->
// "log ->" awaitedPowersOneToTen: Promise<MyMaybeList<Promise<number>>>
Promise { <pending> }
// Promise { <pending> } will resolve into ->

// awaitedPowersOneToTen.then(awaitedList => console.log(awaitedList)); ->
// console.log(awaitedList) ->
// "log->" awaitedList: MyMaybeList<Promise<number>>
// instead of a -> MyMaybeList { Promise<number> }
// in fact is a (should be) -> Promise {  MyMaybeList<number> }
MyMaybeList {
  values: [
     1,  4,  9, 16,  25,
    36, 49, 64, 81, 100
  ]
}
*/