Swift research about capture in closure

capture_test.swift

var x: X? = X()

// leaks if closure1 is called, and it does not capture self by [unowned self]
//x!.closure1()
// if capture self, crashes because x is deallocated befor closure is called.
x!.method()

x = nil

extension NSTimer {
  class NSTimerCallbackHolder : NSObject {
    var callback: () -> ()
    
    init(callback: () -> ()) {
      self.callback = callback
    }
    
    func tick(timer: NSTimer) {
      callback()
    }
  }
  
  class func scheduledTimerWithTimeInterval(ti: NSTimeInterval, repeats yesOrNo: Bool, closure: () -> ()) -> NSTimer! {
    var holder = NSTimerCallbackHolder(callback: closure)
    holder.callback = closure
    
    return NSTimer.scheduledTimerWithTimeInterval(ti, target: holder, selector: Selector("tick:"), userInfo: nil, repeats: yesOrNo)
  }
}

extension NSTimer {
  class func setTimeout(ti: NSTimeInterval, closure: ()->()) {
    NSTimer.scheduledTimerWithTimeInterval(ti, repeats: false, closure: closure)
  }
}

class X {
  var x = 0
  
  deinit {
    println("X deallocated")
  }
  
  func method() {
    NSTimer.setTimeout(3.0, closure: {
      // crashed if captured by `[unowned self] in`
      println(self.x+1)
    })
  }
  
  lazy var closure1: ()->() = { [unowned self] in
    // leaks without `[unowned self] in`
    println(self.x)
  }
}