Simulator vs real device return different weekOfYear from Date

Question

I have a Date object from which I need to get a weekOfYear and my code works great on a real device, but it's one weekOfYear ahead on the simulator if I select Sunday. All other days of the week work fine.

I know the simulator uses the mac's date and time, but both the mac and the real device are set to auto, same time zone, same settings.

let wednesday: Date? = calendar.date(from: DateComponents(year: 2020, month: 10, day: 14))
let sunday: Date? = calendar.date(from: DateComponents(year: 2020, month: 10, day: 18))
    
print("\(wednesday?.weekOfYear) vs \(sunday?.weekOfYear)")
// In the simulator this prints Optional(42) vs Optional(43)
// On a real device this prints Optional(42) vs Optional(42)

Any idea what I'm doing wrong? Does it have anything to do with daylight savings time? The date objects themselves are printed as 2020-10-13 23:00:00 +0000 and 2020-10-17 23:00:00 +0000, but nonetheless, adding 1h for DST should mean it's still Sunday the 18th.

Thanks in advance for any tips.

Update

Thanks for the comments everyone, they helped me find the issue.

The calendar I am using is this:

var calendar: Calendar {
    var calendar = Calendar(identifier: .iso8601)
    calendar.firstWeekday = 2
    return calendar
}

And I have a Date extension to get .weekday which looks like this:

extension Date {
    var weekday: Int { return Calendar.current.component(.weekday, from: self) }
}

So the problem was that I was not using my iso8601 calendar, which starts the week on Monday. I changed it to my calendar and it now works.

Answer 1

As I already mentioned in my comment the problem is the calendar ISO8601 you were using. The first weekday of that calendar is Monday while the current calendar (probably Gregorian) the first weekday is Sunday.

Answer 2

Perhaps there is a difference between the simulator and the real device. Becausue it has a different locale timeZone, please ensure they are same.