Proposal: Progress for all, any, when about promises HOT 6 CLOSED

let progress = Progress(totalUnitCount: 4) // promises count

when([
    Promise<String> { fulfill, reject in
        DispatchQueue.main.asyncAfter(deadline: .now() + 1, execute: {
            print("1")
            
            progress.completedUnitCount += 1
            fulfill("1")
        })
    },
    
    Promise { fulfill, reject in
        DispatchQueue.main.asyncAfter(deadline: .now() + 2, execute: {
            print("2")
            
            progress.completedUnitCount += 1
            fulfill("2")
        })
    },
    
    Promise { fulfill, reject in
        DispatchQueue.main.asyncAfter(deadline: .now() + 3, execute: {
            print("3")
            
            progress.completedUnitCount += 1
            fulfill("3")
        })
    },
    
    Promise { fulfill, reject in
        DispatchQueue.main.asyncAfter(deadline: .now() + 4, execute: {
            print("4")
            
            progress.completedUnitCount += 1
            fulfill("4")
        })
    }
    ])
    .then({ (_) in
        print("DONE")
    })

func subtask(_ overallProgress: Progress) -> Promise<Void> {
  let progress = Progress(totalUnitCount: 10, parent: overallProgress, pendingUnitCount: 1)
  return Promise<Void> {
    guard isEverythingStillOK else {
      progress.cancel()
      throw MyError.somethingIsNotOK
    }
    progress.completedUnitCount = progress.totalUnitCount // Complete the child progress
    return ()
  }
}

let overallProgress = Progress(totalUnitCount: 2)
when(subtask(overallProgress), subtask(overallProgress)).then { _ in
  // At least one subtask has succeeded
}
// Observe overallProgress.fractionCompleted

when([Promise<T>], progress: Progress? = nil)