Swift - Add N month to date

Question

I have used the following code to generate dates between two dates. It works in all cases where the day of the month is less than 28.

extension Date {
      public  func addMonth(n: Int) -> Date {
        let calendar = Calendar.current
        return calendar.date(byAdding: .month, value: n, to: self)!
    }
    public  func addYear(n: Int) -> Date {
        let calendar = Calendar.current
        return calendar.date(byAdding: .year, value: n, to: self)!
    }

    public   var monthName: String {
        let calendar = Calendar.current
        let monthInt = calendar.component(.month, from: self)
        return calendar.monthSymbols[monthInt-1]
    }
}

var date = Date()

repeat {
    date = date.addMonth(n: 1)
    print("\(date) \(date.monthName) ")
} while date <= Date().addYear(n: 2)

Result

2020-07-30 13:31:14 +0000 July 
2020-08-30 13:31:14 +0000 August 
2020-09-30 13:31:14 +0000 September 
2020-10-30 14:31:14 +0000 October 
2020-11-30 14:31:14 +0000 November 
2020-12-30 14:31:14 +0000 December 
2021-01-30 14:31:14 +0000 January 
2021-02-28 14:31:14 +0000 February 
2021-03-28 13:31:14 +0000 March 
2021-04-28 13:31:14 +0000 April 
2021-05-28 13:31:14 +0000 May 
2021-06-28 13:31:14 +0000 June 
2021-07-28 13:31:14 +0000 July 
2021-08-28 13:31:14 +0000 August 
2021-09-28 13:31:14 +0000 September 
2021-10-28 13:31:14 +0000 October 
2021-11-28 14:31:14 +0000 November 
2021-12-28 14:31:14 +0000 December 
2022-01-28 14:31:14 +0000 January 
2022-02-28 14:31:14 +0000 February 
2022-03-28 13:31:14 +0000 March 
2022-04-28 13:31:14 +0000 April 
2022-05-28 13:31:14 +0000 May 
2022-06-28 13:31:14 +0000 June 
2022-07-28 13:31:14 +0000 July 

Expected result

I expect the result to be either 28 or 30.

 2020-07-30 13:31:14 +0000 July
 2020-08-30 13:31:14 +0000 August
 2020-09-30 13:31:14 +0000 September
 2020-10-30 14:31:14 +0000 October
 2020-11-30 14:31:14 +0000 November
 2020-12-30 14:31:14 +0000 December
 2021-01-30 14:31:14 +0000 January
 2021-02-28 14:31:14 +0000 February
 2021-03-30 13:31:14 +0000 March
 2021-04-30 13:31:14 +0000 April
 2021-05-30 13:31:14 +0000 May
 2021-06-30 13:31:14 +0000 June
 2021-07-30 13:31:14 +0000 July
 2021-08-30 13:31:14 +0000 August
 2021-09-30 13:31:14 +0000 September
 2021-10-30 13:31:14 +0000 October
 2021-11-30 14:31:14 +0000 November
 2021-12-30 14:31:14 +0000 December
 2022-01-30 14:31:14 +0000 January
 2022-02-28 14:31:14 +0000 February
 2022-03-30 13:31:14 +0000 March
 2022-04-30 13:31:14 +0000 April
 2022-05-30 13:31:14 +0000 May
 2022-06-30 13:31:14 +0000 June
 2022-07-30 13:31:14 +0000 July

Does Calendar has built-in functionality to achieve this?

Answer 1

As you observed, adding 1 month n times is not the same as adding n month. Apparently you want the latter, e.g. like this:

let now = Date()
let finalDate = now.addYear(n: 2)

for n in 1... {
    let date = now.addMonth(n: n)
    print("\(date) \(date.monthName) ")
    if date > finalDate { break }
}

Or this:

let now = Date()
let finalDate = now.addYear(n: 2)

let dates = (1...).lazy.map { now.addMonth(n: $0) }
    .prefix(while: { $0 <= finalDate } )
for date in dates {
    print("\(date) \(date.monthName)")
}