In WWDC 2014 session 403 Intermediate Swift and transcript, there was the following slide

The speaker said in that case, if we don't use [unowned self] there, it will be a memory leak. Does it mean we should always use [unowned self] inside closure?

On line 64 of ViewController.swift of the Swift Weather app, I don't use [unowned self]. But I update the UI by using some @IBOutlets like self.temperature and self.loadingIndicator. It may be OK because all @IBOutlets I defined are weak. But for safety, should we always use [unowned self]?

class TempNotifier {
  var onChange: (Int) -> Void = {_ in }
  var currentTemp = 72
  init() {
    onChange = { [unowned self] temp in
      self.currentTemp = temp
    }
  }
}