public func range(of unit: Calendar.Unit, start datep: AutoreleasingUnsafeMutablePointer<NSDate?>?, interval tip: UnsafeMutablePointer<TimeInterval>?, for date: Date) -> Bool

func numberOfDaysUntilDate() -> NSInteger {
        let units: Calendar.Unit = [.day]
        
        var fromDate: NSDate?
        var toDate: NSDate?
        var duration: TimeInterval = 0
        
        calendar.range(of: units, start: &fromDate, interval: &duration, for: Date())
        calendar.range(of: units, start: &toDate, interval: &duration, for: self)
        
        let components = calendar.components(units, from: fromDate as! Date, to: toDate as! Date, options: Calendar.Options(rawValue: 0))
        return components.day!
    }