chain Task.all more than once, last then not called.

[taka0125]

Under the following conditions, last then not called.

• Task.all chain more than once
• all tasks is empty

what would be a good way to do it?

Sample code

final class Image {
  let url: String

  var downloaded: Bool = false
  var converted: Bool = false

  typealias DownloadTask = Task<NSProgress, String, NSError?>
  typealias ConvertTask = Task<NSProgress, String, NSError?>

  init(url: String) {
    self.url = url
  }

  func download() -> DownloadTask {
    return DownloadTask { progress, fulfill, reject, configure in
      // download image and cache
      self.downloaded = true
      return fulfill("path to image")
    }
  }

  func convert() -> ConvertTask {
    return ConvertTask { progress, fulfill, reject, configure in
      // convert image
      self.converted = true
      return fulfill("path to converted image")
    }
  }
}

func downloadAndConvertAll() {
  let images = [
    Image(url: "http://example.com/1.jpg"),
    Image(url: "http://example.com/2.jpg"),
    Image(url: "http://example.com/3.jpg"),
  ]

  // I want to exclude downloaded image
  let downloadTasks = images.filter { !$0.downloaded }.map { $0.download() }

  // downloadTasks.count == 0 and convertTasks.count == 0 => doSomething not called
  Task.all(downloadTasks).then { _ -> Task<Image.ConvertTask.BulkProgress, [String], NSError?> in
    // I want to exclude converted image
    let convertTasks = images.filter { !$0.converted }.map { $0.convert() }
    return Task.all(convertTasks)
  }.then { _ in
    doSomething()
  }
}

func doSomething() {
  print("doSomething")
}

found workaround

Task.all(downloadTasks.count > 0 ? downloadTasks : [Image.DownloadTask(value: "dummy")])

and

Task.all(convertTasks.count > 0 ? convertTasks : [Image.ConvertTask(value: "dummy")])

[inamiy]

Thanks for the catch!
What is happening in your code is Task.all([] /* empty */).then { /* this will never be called in ver 4.2.0 */ }.
I have never assumed tasks-argument to be empty, so fulfilling with empty array should solve this issue. I will address that in a moment.

[inamiy]

Done in #60.

[taka0125]

👍

Thank you for your quick response!