swiftで２つの年月日秒の差分を取りたい

簡単にできるかと思ったけど意外と時間かかったし忘れそうなのでメモ

let start = "2000/10/09 23:58:59"
let end = "2041/10/09 00:00:00"

let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy/MM/dd HH:mm:ss"

let startDate:NSDate? = dateFormatter.dateFromString(start)
let endDate:NSDate? = dateFormatter.dateFromString(end)

let cal = NSCalendar.currentCalendar()
let calUnit:NSCalendarUnit = .CalendarUnitSecond | .CalendarUnitMinute | .CalendarUnitHour | .CalendarUnitDay | .CalendarUnitYear

let components = cal.components(calUnit, fromDate: startDate!, toDate: endDate!, options: nil)

println(components.year)   //40
println(components.day)    //364
println(components.hour)   //0
println(components.minute) //1
println(components.second) //1

ブログに書いてみたけどやっぱりブログが続けられないのでこっちで書き溜めたい。