The Date-ing Game - iOS Conf SG, Singapore, January 2024

A fun journey through how we take something as simple as a single point in time and find all kinds of new and interesting ways to screw it up royally, especially within the Apple ecosystem.

1. THE DATE-ING GAME IOS CONF SG | SINGAPORE | JANUARY 2024 ELLEN SHAPIRO | MASTODON.SOCIAL/@DESIGNATEDNERD | PIXITEAPPS.COM
4. TIME SEEMS EASY
5. TIME SEEMS EASY ( SPOILER ALERT: IT IS NOT )
6. let now = Date()
7. 60 * 60
8. 60 * 60 * 24
9. 60 * 60 * 24 * 365
10. let now = Date.now let oneYear = TimeInterval(60 * 60 * 24 * 365) let oneYearLater = now.addingTimeInterval(oneYear) print("Now: \(now).\nOne year from now: \(oneYearLater)")
11. let now = Date.now let oneYear = TimeInterval(60 * 60 * 24 * 365) let oneYearLater = now.addingTimeInterval(oneYear) print("Now: \(now).\nOne year from now: \(oneYearLater)")
13. !
15. DATE
16. THE ! DEFINITION A specific point in time, independent of any calendar or time zone.
17. MY DEFINITION A fixed point in time
18. .timeIntervalSince1970
19. .timeIntervalSince1970 .timeIntervalSinceReferenceDate
20. .timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate
21. .timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001
22. .timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001 .timeIntervalBetween1970AndReferenceDate
23. .timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001 .timeIntervalBetween1970AndReferenceDate 978,307,200 seconds
24. previousSeconds += 1
25. ! !
26. CALENDAR
27. THE ! DEFINITION A definition of the relationships between calendar units and absolute points in time, providing features for calculation and comparison of dates
28. MY DEFINITION The only way to relate an absolute point in time to anything humans will actually be able to understand
29. 404 DAY NOT FOUND
31. Calendar.Identifier.gregorian
32. Painted by Bartolomeo Passarotti
34. !
35. 365.25
36. 365.2425
37. Painted by Bartolomeo Passarotti
39. Calendar.Identifier.japan
42. !
43. Calendar.identifier.hebrew Calendar.idenfier.islamic Calendar.identifier.chinese Calendar.identifier.indian
44. DO NOT TRY THIS (MANUALLY) AT HOME
45. Calendar(identifier: .gregorian)
46. Calendar.autoupdatingCurrent
47. DATE FORMATTER
48. THE ! DEFINITION Instances of DateFormatter create string representations of Date objects, and convert textual representations of dates and times into Date objects.
49. MY DEFINITION The thing you should use to turn a Date into a user-facing string.
50. let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent
51. let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now))
52. let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now)) // prints: (nothing!)
53. let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent formatter.dateFormat = "MM-dd-yyyy" print(formatter.string(from: now)) // prints: "01-19-2024"
55. let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent formatter.dateStyle = .full print(formatter.string(from: now)) // prints: "Friday, 19 January 2024"
56. let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent formatter.dateStyle = .full print(formatter.string(from: now)) // prints: "Friday, 19 January 2024" formatter.locale = Locale(identifier: "en_US")
57. let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent formatter.dateStyle = .full print(formatter.string(from: now)) // prints: "Friday, 19 January 2024" formatter.locale = Locale(identifier: "en_US") print(formatter.string(from: now)) // prints: "Friday, January 19, 2024"
58. let now = Date() let aucFormatter = DateFormatter() aucFormatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now)) // prints: "Friday, 19 January 2024" let islamicFormatter = DateFormatter() islamicFormatter.calendar = Calendar(identifier: .islamic)
59. let now = Date() let aucFormatter = DateFormatter() aucFormatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now)) // prints: "Friday, 19 January 2024" let islamicFormatter = DateFormatter() islamicFormatter.calendar = Calendar(identifier: .islamic) islamicFormatter.dateStyle = .full // prints: "Friday, 8 Rajab 1445 AH"
60. let now = Date() let aucFormatter = DateFormatter() aucFormatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now)) // prints: "Friday, 19 January 2024" let islamicFormatter = DateFormatter() islamicFormatter.calendar = Calendar(identifier: .islamic) islamicFormatter.dateStyle = .full print(islamicFormatter.string(from: now)) // prints: "Friday, 8 Rajab 1445 AH" islamicFormatter.locale = Locale(identifier: "en_US") print(islamicFormatter.string(from: now)) // prints: "Friday, Rajab 8, 1445 AH"
61. OTHER USEFUL DATE FORMATTERS
62. OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter
63. OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter
64. OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter > ISO8601DateFormatter
65. OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter > ISO8601DateFormatter > RelativeDateTimeFormatter *
66. OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter > ISO8601DateFormatter > RelativeDateTimeFormatter * * swift only
68. JUMP BACK AND FORTH BETWEEN SWIFT AND OBJC LESS FREQUENTLY
69. DATE COMPONENTS
70. THE ! DEFINITION A date or time specified in terms of units (such as year, month, day, hour, and minute) to be evaluated in a calendar system and time zone.
71. MY DEFINITION How to define which parts of a date you actually care about
75. dateComponents(_ components: Set<Calendar.Component>, from date: Date) -> DateComponents date(from: DateComponents) -> Date
76. GETTING COMPONENTS OUT OF A DATE
77. let talkTime = ISO8601DateFormatter() .date(from: "2024-01-19T14:10:00+08:00")!
78. let talkTime = ISO8601DateFormatter() .date(from: "2024-01-19T14:10:00+08:00")! let timeComponents = gregorianCalendar .dateComponents([.hour, .minute], from: talkTime)
79. let talkTime = ISO8601DateFormatter() .date(from: "2024-01-19T14:10:00+08:00")! let timeComponents = gregorianCalendar .dateComponents([.hour, .minute], from: talkTime) let hour = timeComponents.hour print(hour) // prints "Optional(14)" let minute = timeComponents.minute print(minute) // prints "Optional(10)"
80. let talkTime = ISO8601DateFormatter() .date(from: "2024-01-19T14:10:00+08:00")! let timeComponents = gregorianCalendar .dateComponents([.hour, .minute], from: talkTime) let hour = timeComponents.hour print(hour) // prints "Optional(14)" let minute = timeComponents.minute print(minute) // prints "Optional(10)" let second = timeComponents.second
81. let talkTime = ISO8601DateFormatter() .date(from: "2024-01-19T14:10:00+08:00")! let timeComponents = gregorianCalendar .dateComponents([.hour, .minute], from: talkTime) let hour = timeComponents.hour print(hour) // prints "Optional(14)" let minute = timeComponents.minute print(minute) // prints "Optional(10)" let second = timeComponents.second print(second) // prints "nil"
83. TURNING COMPONENTS INTO A DATE
84. let components = DateComponents(year: 2024, month: 1, day: 19)
85. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult))
86. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024"
87. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! gregorianFormatter.timeStyle = .short print(gregorianFormatter.string(from: gregorianResult))
88. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! gregorianFormatter.timeStyle = .short print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024 at 12:00AM"
89. let components = DateComponents(year: 2024) let gregorianResult = gregorianCalendar.date(from: components)! gregorianFormatter.timeStyle = .short print(gregorianFormatter.string(from: gregorianResult)) // prints "Monday, 1 January 2024 at 12:00 AM"
90. let components = DateComponents(year: 2024, month: 1, day: 19, hour: 14, minute: 10) let gregorianResult = gregorianCalendar.date(from: components)! gregorianFormatter.timeStyle = .short print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024 at 2:10 PM"
91. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024"
92. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024" let islamicResult = islamicCalendar.date(from: components)!
93. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024" let islamicResult = islamicCalendar.date(from: components)! print(gregorianFormatter.string(from: islamicResult))
94. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024 let islamicResult = islamicCalendar.date(from: components)! print(gregorianFormatter.string(from: islamicResult)) // prints "Tuesday, 10 May 2585"
95. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024 let islamicResult = islamicCalendar.date(from: components)! print(gregorianFormatter.string(from: islamicResult)) // prints "Tuesday, 10 May 2585" print(islamicFormatter.string(from: islamicResult))
96. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024 let islamicResult = islamicCalendar.date(from: components)! print(gregorianFormatter.string(from: islamicResult)) // prints "Tuesday, 10 May 2585" print(islamicFormatter.string(from: islamicResult)) // prints "Tuesday, 19 Muharram 2024 AH"
97. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024 let islamicResult = islamicCalendar.date(from: components)! print(gregorianFormatter.string(from: islamicResult)) // prints "Tuesday, 10 May 2585" print(islamicFormatter.string(from: islamicResult)) // prints "Tuesday, 19 Muharram 2024 AH"
99. ¯\_(ツ)_/¯
100. let components = DateComponents(year: 2024, month: 1, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Friday, 19 January 2024 print(islamicFormatter.string(from: gregorianResult)) // prints "Friday, 8 Rajab 1445 AH"
101. .timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001 .timeIntervalBetween1970AndReferenceDate 978,307,200 seconds
102. UTC
103. UTC COORDINATED UNIVERSAL TIME
104. UTC UNIVERSAL TIME, COORDINATED!
105. GOES-16 satellite
106. TIME ZONE
107. THE ! DEFINITION Information about standard time conventions associated with a specific geopolitical region.
108. MY DEFINITION The way humans reconcile the rotation of the earth and a need to coordinate time across physical and political boundaries
109. !
110. BOSTON: 71.0552° W NYC: 73.9935° W
111. ! ⌚
112. ! "
113. ! GMT
117. 360 / 24 = 15
120. !
121. https://www.bbc.com/news/world-asia-16351377
122. https://www.bbc.com/news/world-asia-16351377
123. SERIOUSLY, DO NOT TRY THIS (MANUALLY) AT HOME
124. let allTimeZones = TimeZone.knownTimeZoneIdentifiers .compactMap { TimeZone(identier: $0) }
127. TimeZone.autoupdatingCurrent
128. let utcTimeZone = TimeZone(identifier: "UTC")!
135. let utcTimeZone = TimeZone(identifier: "UTC")! print(utcTimeZone.identifier)
136. let utcTimeZone = TimeZone(identifier: "UTC")! print(utcTimeZone.identifier) // prints: "GMT"
137. TimeZone.secondsFromGMT(for: Date)
138. GENERAL ADVICE
139. STORE ONLY THE COMPONENTS YOU NEED
140. https://www.pixiteapps.com/apps/planner-journal-zinnia
142. THIS IS VERY EASY TO OVERTHINK
143. THIS IS ALSO VERY EASY TO UNDERESTIMATE
144. TEST YOUR DATES AND TIMES
145. CREATING A DATE IN ONE TIME ZONE READING IT IN ANOTHER
146. WATCH OUT FOR WHAT TIME YOUR CI THINKS IT IS
147. ONE COMPONENT IS SUDDENLY LOWER
148. ONE COMPONENT IS SUDDENLY LOWER > Day Rollovers
149. ONE COMPONENT IS SUDDENLY LOWER > Day Rollovers > Month Rollovers
150. ONE COMPONENT IS SUDDENLY LOWER > Day Rollovers > Month Rollovers > Year Rollovers
151. OCCASIONAL WEIRDNESS
152. OCCASIONAL WEIRDNESS > Leap Year Rollovers
153. OCCASIONAL WEIRDNESS > Leap Year Rollovers > Years With Extra Months in Lunisolar Calendars
154. OCCASIONAL WEIRDNESS > Leap Year Rollovers > Years With Extra Months in Lunisolar Calendars > Daylight Savings Time Rollovers
155. THINGS I SCREWED UP JUST LAST WEEK
156. CALENDAR + DATECOMPONENTS Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)
158. extension Date { func formattedNextHoursAdjsutingComponents(count: Int) -> [String] { var components = Calendar.autoupdatingCurrent .dateComponents([.year, .month, .day, .hour, .minute], from: self) let originalHour = components.hour! var formattedHours = [String]() for hour in 0..<count { components.hour = originalHour + hour let updatedDate = Calendar.autoupdatingCurrent .date(from: components) let formatted = formatter.string(from: updatedDate) formattedHours.append(formatted) } return formattedHours } }
159. extension Date { func formattedNextHoursAdjsutingComponents(count: Int) -> [String] { var components = Calendar.autoupdatingCurrent .dateComponents([.year, .month, .day, .hour, .minute], from: self) let originalHour = components.hour! var formattedHours = [String]() for hour in 0..<count { components.hour = originalHour + hour let updatedDate = Calendar.autoupdatingCurrent .date(from: components) let formatted = formatter.string(from: updatedDate) formattedHours.append(formatted) } return formattedHours } }
160. func formattedNextHoursAddingComponents(count: Int) -> [String] { var formattedHours = [String]() for hour in 0..<count { let updatedDate = Calendar.autoupdatingCurrent .date(byAdding: DateComponents(hour: hour), to: self)! let formatted = formatter.string(from: updatedDate) formattedHours.append(formatted) } return formattedHours }
161. func formattedNextHoursAddingComponents(count: Int) -> [String] { var formattedHours = [String]() for hour in 0..<count { let updatedDate = Calendar.autoupdatingCurrent .date(byAdding: DateComponents(hour: hour), to: self)! let formatted = formatter.string(from: updatedDate) formattedHours.append(formatted) } return formattedHours }
162. let now = Date() let nowAdjustingComponents = now .formattedNextHoursAdjustingComponents(count: 12) .joined(separator: "\n") let nowAddingComponents = now .formattedNextHoursAddingComponents(count: 12) .joined(separator: "\n")
163. // March 9, 2024 at 7pm Eastern Time let springForward = ISO8601DateFormatter().date(from: "2024-03-10T00:00:00Z")! formatter.timeZone = TimeZone(identifier: "America/New_York")! let springForwardAdjustingComponents = springForward .formattedNextHoursAdjustingComponents(count: 12) .joined(separator: "\n") let springForwardAddingComponents = springForward .formattedNextHoursAddingComponents(count: 12) .joined(separator: "\n")
164. NOW
165. ADJUSTING ADDING
166. ADJUSTING ADDING ✅
167. SPRING FORWARD
168. ADJUSTING ADDING
169. ADJUSTING ADDING
170. ADJUSTING ADDING
171. ADJUSTING ADDING
172. ADJUSTING ADDING ❌
176. CALENDAR + DATECOMPONENTS Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)
177. CALENDAR + DATECOMPONENTS Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)
178. CALENDAR + DATECOMPONENTS /// Find the closest matching date to the given date components Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)
179. March 9 2024 25:00
180. March 9 2024 25:00 -> March 10 2024 01:00
181. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00
182. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00
183. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00 -> March 10 2024 02:00 ->
184. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00 -> March 10 2024 02:00 -> Does not exist, what's the closest match?
185. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00 -> March 10 2024 02:00 -> Does not exist, what's the closest match? -> March 10 2024 03:00
186. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00 -> March 10 2024 02:00 -> Does not exist, what's the closest match? -> March 10 2024 03:00 March 9 2024 27:00
187. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00 -> March 10 2024 02:00 -> Does not exist, what's the closest match? -> March 10 2024 03:00 March 9 2024 27:00 -> March 10 2024 03:00
188. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00 -> March 10 2024 02:00 -> Does not exist, what's the closest match? -> March 10 2024 03:00 March 9 2024 27:00 -> March 10 2024 03:00 -> March 10 2024 03:00
189. March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00 -> March 10 2024 02:00 -> Does not exist, what's the closest match? -> March 10 2024 03:00 ! March 9 2024 27:00 -> March 10 2024 03:00 -> March 10 2024 03:00 !
190. CALENDAR + DATECOMPONENTS /// Find the closest matching date to the given date components Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)
191. CALENDAR + DATECOMPONENTS /// Find the closest matching date to the given date components Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) /// Take the passed-in date and add the passed-in components Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)
192. March 9 2024 17:00 + 8h
193. March 9 2024 17:00 + 8h -> March 10 2024 01:00
194. March 9 2024 17:00 + 8h -> March 10 2024 01:00 March 9 2024 17:00 + 9h
195. March 9 2024 17:00 + 8h -> March 10 2024 01:00 March 9 2024 17:00 + 9h -> March 10 2024 03:00
196. March 9 2024 17:00 + 8h -> March 10 2024 01:00 March 9 2024 17:00 + 9h -> March 10 2024 03:00 March 9 2024 17:00 + 10h
197. March 9 2024 17:00 + 8h -> March 10 2024 01:00 March 9 2024 17:00 + 9h -> March 10 2024 03:00 March 9 2024 17:00 + 10h -> March 10 2024 04:00
199. OBLIGATORY SUMMARY SLIDE
200. OBLIGATORY SUMMARY SLIDE > Computers think about dates and time as numeric offsets from a specific point in time
201. OBLIGATORY SUMMARY SLIDE > Computers think about dates and time as numeric offsets from a specific point in time > Humans think about dates in a lot of different ways
202. OBLIGATORY SUMMARY SLIDE > Computers think about dates and time as numeric offsets from a specific point in time > Humans think about dates in a lot of different ways > Let ! handle as much of this for you as possible
203. OBLIGATORY SUMMARY SLIDE > Computers think about dates and time as numeric offsets from a specific point in time > Humans think about dates in a lot of different ways > Let ! handle as much of this for you as possible > Use date and time styles rather than specific formats if you're displaying a date to a user
204. OBLIGATORY SUMMARY SLIDE > Computers think about dates and time as numeric offsets from a specific point in time > Humans think about dates in a lot of different ways > Let ! handle as much of this for you as possible > Use date and time styles rather than specific formats if you're displaying a date to a user > Test the crap out of transition points
206. DONATION LINKS https://www.ncis.com.sg/Give- a-Gift/Pages/Donate-Now.aspx https:// glioblastomafoundation.org/ get-involved/donate
207. THANK YOU!
208. DATE AND TIME LINKS! > https://developer.apple.com/videos/play/ wwdc2020/10160/ - Apple's guide to displaying content humans understand across the world > https://www.youtube.com/watch?v=-5wpm-gesOY - Tom Scott from 2013 on the Problem With Time And Time Zones, capturing the exasperation beautifully
209. LINKS: SERIOUSLY, LISTEN TO DAVE DELONG EDITION > https://yourcalendricalfallacyis.com, a fine listing of just a few of the many, many, many ways to screw up dates, times, and calendars. > https://vimeo.com/865876497, his 2023 NSSpain talk "The Temporal Axis of Space-Time" drawing parallels between how we think about space and how we think about time