Time vs Calendar: One is Easy, the Other Hard

Leap Years!
Daylight Savings Time!
Time Zones!

Approach Calendars with humility - this presentation compares Time and Calendars, shows you some common pitfalls, and concludes with Swift 5.5 examples.

Transcript

1. November 2nd, 2021 TIME vs CALENDAR One is Easy, the Other Hard
2. November 2nd, 2021 TIME: What is it? CALENDAR: What is it? CODE EXAMPLES: Stay Tuned
3. TIME CALENDAR November 2nd, 2021
4. EASY CALENDAR November 2nd, 2021
5. EASY HARD November 2nd, 2021
6. SCALAR HARD November 2nd, 2021
7. SCALAR EDGE CASES November 2nd, 2021
8. TIME CALENDAR November 2nd, 2021
9. TIME Number of “time-units” since “starting point” November 2nd, 2021 Number of seconds since January 1st, 2001
10. CALENDAR ROMAN JULIAN GREGORIAN HOLOCENE HEBREW ISLAMIC BRITISH REGNAL YEAR many, many others November 2nd, 2021
11. CALENDAR ROMAN (year #, month names, day names, manual lunar to solar fix) JULIAN (year #, month names, day numbers, automatic lunar to solar fix) GREGORIAN (slightly better automatic lunar to solar fix) HOLOCENE (year #) November 2nd, 2021
12. TIME CALENDAR November 2nd, 2021
13. TIME CALENDAR November 2nd, 2021 0
14. TIME GREGORIAN CALENDAR November 2nd, 2021 0 1582 leap year inconsistent month length leap second time zones daylight savings
15. TIME CALENDAR November 2nd, 2021
16. stopwatch, alarms, orbital mechanics November 2nd, 2021 CALENDAR
17. stopwatch, alarms, orbital mechanics November 2nd, 2021 appointments, alarms, modern life
18. STEP 1: In what domain is my problem? November 2nd, 2021 STEP 2: If Calendar, have some humility
19. CALENDAR DOMAIN MISTAKE 1: Calendar Day = (seconds / minute ) * (minutes / hour ) * (hours / day) = 60 * 60 * 24 Tomorrow = current day + Calendar Day November 2nd, 2021 CALENDAR DOMAIN MISTAKE 2: I’m smart enough to avoid Mistake 1! I’ll use Time and handle the edge cases myself!
20. CODE EXAMPLES November 2nd, 2021
21. Xcode: Version 13.1 (13A1030d) Swift: Version 5.5.1 November 2nd, 2021 CODE EXAMPLES
22. EXAMPLE 1: STOPWATCH November 2nd, 2021 Show elapsed time between two clicks
23. EXAMPLE 1: STOPWATCH November 2nd, 2021 Show elapsed time between two clicks Is the domain TIME or CALENDAR?
24. EXAMPLE 1: STOPWATCH November 2nd, 2021 Show elapsed time between two clicks Is the domain TIME or CALENDAR? Store Current Time of Start Click Store Current Time End Click Print End - Start
25. EXAMPLE 1: STOPWATCH November 2nd, 2021 let timeStart = Date().timeIntervalSinceReferenceDate print(timeStart) let timeEnd = Date().timeIntervalSinceReferenceDate print(timeEnd) print(timeEnd - timeStart)
26. EXAMPLE 2: APPOINTMENT November 2nd, 2021 Show appointment day, month, year
27. EXAMPLE 2: APPOINTMENT November 2nd, 2021 Show appointment day, month, year Is the domain TIME or CALENDAR?
28. EXAMPLE 2: APPOINTMENT November 2nd, 2021 Show appointment day, month, year Is the domain TIME or CALENDAR? Create Calendar Object Set day, month, year Create and print calendar object
29. EXAMPLE 2: APPOINTMENT November 2nd, 2021 let exampleCalendar = Calendar(identifier: .gregorian) var exampleDateComponents = DateComponents() exampleDateComponents.year = 2021 exampleDateComponents.month = 11 exampleDateComponents.day = 2 exampleDateComponents.timeZone = TimeZone(abbreviation: "CST") exampleDateComponents.hour = 22 exampleDateComponents.minute = 34 let appointmentDate = exampleCalendar.date(from: exampleDateComponents) ?? Date() print(appointmentDate)
30. EXAMPLE 3: HOURS UNTIL APPOINTMENT November 2nd, 2021 Show hours from now until appointment Is the domain TIME or CALENDAR?
31. EXAMPLE 3: HOURS UNTIL APPOINTMENT November 2nd, 2021 Show hours from now until appointment Is the domain TIME or CALENDAR? Store Current Time A Get Time of Appointment B Print B - A
32. EXAMPLE 3: HOURS UNTIL APPOINTMENT November 2nd, 2021 let timeCurrent = Date().timeIntervalSinceReferenceDate let appointmentDateAsTime = appointmentDate.timeIntervalSinceReferenceDate print((appointmentDateAsTime - timeCurrent) / (60 * 60))
33. November 2nd, 2021 TIME vs CALENDAR One is Easy, the Other Hard