import Cocoa

/* How many days are there in the month of December 2023? */

let calendar = Calendar.current
let dateComponents = DateComponents(calendar: calendar, year: 2023, month: 12)
let date = calendar.date(from: dateComponents)!
let range = calendar.range(of: .day, in: .month, for: date)!
let days = range.count

print("There are \(days) days in December 2023")

Output

There are 31 days in December 2023