core_animation_demo_2.swift

  demoView.frame = CGRectMake(0, 0, 100, 100)
  demoView.backgroundColor = UIColor.purpleColor()
  
  self.backgroundColor = UIColor.greenColor()
  
  UIView.animateWithDuration(3, delay: 0, options: [.CurveLinear, .AllowUserInteraction],
      animations: { () -> Void in
          self.backgroundColor = UIColor.grayColor()
          self.demoView.center = CGPointMake(200, 200)
      }) { (Bool) -> Void in
          self.demoView.center = CGPointMake(50, 50)
  }
  puts("foo bar")
}