The Date-ing Game - NSSpain, Logroño, Rioja, September 2024

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THE DATE-ING GAME NSSPAIN | LOGROÑO, RIOJA | SEPTEMBER 2024 ELLEN SHAPIRO | MASTODON.SOCIAL/@DESIGNATEDNERD | PIXITEAPPS.COM

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TIME SEEMS EASY

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TIME SEEMS EASY ( SPOILER ALERT: IT IS NOT )

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let now = Date()

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60 * 60

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60 * 60 * 24

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60 * 60 * 24 * 365

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let now = Date.now let oneYear = TimeInterval(60 * 60 * 24 * 365) let oneYearLater = now.addingTimeInterval(oneYear) print("Now: \(now).\nOne year from now: \(oneYearLater)")

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let now = Date.now let oneYear = TimeInterval(60 * 60 * 24 * 365) let oneYearLater = now.addingTimeInterval(oneYear) print("Now: \(now).\nOne year from now: \(oneYearLater)")

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DATE

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THE ! DEFINITION A specific point in time, independent of any calendar or time zone.

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MY DEFINITION A fixed point in time

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.timeIntervalSince1970

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.timeIntervalSince1970 .timeIntervalSinceReferenceDate

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.timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate

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.timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001

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INT32

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https://en.wikipedia.org/wiki/Year_2038_problem

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https://en.wikipedia.org/wiki/Year_2038_problem

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.timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001 .timeIntervalBetween1970AndReferenceDate

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.timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001 .timeIntervalBetween1970AndReferenceDate 978,307,200 seconds

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previousSeconds += 1

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! !

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CALENDAR

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THE ! DEFINITION A definition of the relationships between calendar units and absolute points in time, providing features for calculation and comparison of dates

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MY DEFINITION The only way to relate an absolute point in time to anything humans will actually be able to understand

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404 DAY NOT FOUND

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Calendar.Identifier.gregorian

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Painted by Bartolomeo Passarotti

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! !

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365.25

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365.2425

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Painted by Bartolomeo Passarotti

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Calendar.Identifier.japan

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Calendar.identifier.hebrew Calendar.idenfier.islamic Calendar.identifier.chinese Calendar.identifier.indian

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DO NOT TRY THIS (MANUALLY) AT HOME

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Calendar(identifier: .gregorian)

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Calendar.autoupdatingCurrent

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DATE FORMATTER

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THE ! DEFINITION Instances of DateFormatter create string representations of Date objects, and convert textual representations of dates and times into Date objects.

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MY DEFINITION The thing you should use to turn a Date into a user-facing string.

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let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent

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let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now))

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let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now)) // prints: (nothing!)

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let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent formatter.dateFormat = "MM-dd-yyyy" print(formatter.string(from: now)) // prints: "09-19-2024"

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let now = Date() let formatter = DateFormatter() formatter.calendar = Calendar.autoupdatingCurrent formatter.dateStyle = .full print(formatter.string(from: now)) // prints: "Thursday, 19 September 2024" formatter.locale = Locale(identifier: "en_US")

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let now = Date() let aucFormatter = DateFormatter() aucFormatter.calendar = Calendar.autoupdatingCurrent print(formatter.string(from: now)) // prints: "Thursday, 19 September 2024" let islamicFormatter = DateFormatter() islamicFormatter.calendar = Calendar(identifier: .islamic)

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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 "Thursday, Rabiʻ I 16, 1446 AH" islamicFormatter.locale = Locale(identifier: "en_GB") print(islamicFormatter.string(from: now)) // prints "Thursday, 16 Rabiʻ I 1446 AH"

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OTHER USEFUL DATE FORMATTERS

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OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter

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OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter

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OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter > ISO8601DateFormatter

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OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter > ISO8601DateFormatter > RelativeDateTimeFormatter *

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OTHER USEFUL DATE FORMATTERS > DateIntervalFormatter > DateComponentsFormatter > ISO8601DateFormatter > RelativeDateTimeFormatter * * swift only

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FORMATSTYLE

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GOSHDARN FORMATSTYLE.COM

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DATE COMPONENTS

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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.

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MY DEFINITION How to define which parts of a date you actually care about

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dateComponents(_ components: Set, from date: Date) -> DateComponents date(from: DateComponents) -> Date

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GETTING COMPONENTS OUT OF A DATE

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let talkTime = ISO8601DateFormatter() .date(from: "2024-09-19T14:30:00+02:00")!

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let talkTime = ISO8601DateFormatter() .date(from: "2024-09-19T14:30:00+02:00")! let timeComponents = gregorianCalendar .dateComponents([.hour, .minute], from: talkTime)

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let talkTime = ISO8601DateFormatter() .date(from: "2024-09-19T14:30:00+02:00")! 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(30)"

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TURNING COMPONENTS INTO A DATE

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let components = DateComponents(year: 2024, month: 9, day: 19)

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let components = DateComponents(year: 2024, month: 9, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult))

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let components = DateComponents(year: 2024, month: 9, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! gregorianFormatter.timeStyle = .short print(gregorianFormatter.string(from: gregorianResult))

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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"

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let components = DateComponents(year: 2024, month: 9, day: 19, hour: 14, minute: 30) let gregorianResult = gregorianCalendar.date(from: components)! gregorianFormatter.timeStyle = .short print(gregorianFormatter.string(from: gregorianResult)) // prints "Thursday, 19 September 2024 at 2:30 PM"

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let components = DateComponents(year: 2024, month: 9, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Thursday, 19 September 2024" let islamicResult = islamicCalendar.date(from: components)! print(gregorianFormatter.string(from: islamicResult))

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let components = DateComponents(year: 2024, month: 9, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Thusrday, 19 September 2024" let islamicResult = islamicCalendar.date(from: components)! print(gregorianFormatter.string(from: islamicResult)) // prints "Saturday, 31 December 2585"

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¯\_(ツ)_/¯

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let components = DateComponents(year: 2024, month: 9, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Thursday, 9 September 2024 print(islamicFormatter.string(from: gregorianResult)) // prints "Thursday, Rabiʻ I 16, 1446 AH"

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let components = DateComponents(year: 2024, month: 9, day: 19) let gregorianResult = gregorianCalendar.date(from: components)! print(gregorianFormatter.string(from: gregorianResult)) // prints "Thursday, 9 September 2024 print(islamicFormatter.string(from: gregorianResult)) // prints "Thursday, Rabiʻ I 16, 1446 AH"

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.timeIntervalSince1970 00:00:00 UTC on 1 January 1970 .timeIntervalSinceReferenceDate 00:00:00 UTC on 1 January 2001 .timeIntervalBetween1970AndReferenceDate 978,307,200 seconds

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UTC

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UTC COORDINATED UNIVERSAL TIME

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UTC UNIVERSAL TIME, COORDINATED!

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TIME ZONE

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THE ! DEFINITION Information about standard time conventions associated with a specific geopolitical region.

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MY DEFINITION The way humans reconcile the rotation of the earth and a need to coordinate time across physical and political boundaries

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BOSTON: 71.0552° W NYC: 73.9935° W

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! ⌚

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! "

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! GMT

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360 / 24 = 15

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https://www.bbc.com/news/world-asia-16351377

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MY DEFINITION The way humans reconcile the rotation of the earth and a need to coordinate time across physical and political boundaries

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MY DEFINITION The way humans reconcile the rotation of the earth* and a need to coordinate time across physical and political boundaries * - mostly

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LTC COORDINATED LUNAR TIME

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https://www.esa.int/Applications/Satellite_navigation/Telling_time_on_the_Moon

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[https://www.whitehouse.gov/wp-content/uploads/2024/04/Celestial-Time-Standardization-Policy.pdf

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SERIOUSLY, DO NOT TRY THIS (MANUALLY) AT HOME

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let allTimeZones = TimeZone.knownTimeZoneIdentifiers .compactMap { TimeZone(identier: $0) }

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https://commons.wikimedia.org/wiki/File:China_%E2%80%93_U.S._area_comparison.jpg

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TimeZone.autoupdatingCurrent

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let utcTimeZone = TimeZone(identifier: "UTC")!

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let utcTimeZone = TimeZone(identifier: "UTC")! print(utcTimeZone.identifier)

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let utcTimeZone = TimeZone(identifier: "UTC")! print(utcTimeZone.identifier) // prints: "GMT"

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TimeZone.secondsFromGMT(for: Date)

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GENERAL ADVICE

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STORE ONLY THE COMPONENTS YOU NEED

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https://www.pixiteapps.com/apps/planner-journal-zinnia

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THIS IS VERY EASY TO OVERTHINK

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THIS IS ALSO VERY EASY TO UNDERESTIMATE

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TEST YOUR DATES AND TIMES

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CREATING A DATE IN ONE TIME ZONE READING IT IN ANOTHER

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WATCH OUT FOR WHAT TIME YOUR CI THINKS IT IS

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ONE COMPONENT IS SUDDENLY LOWER

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ONE COMPONENT IS SUDDENLY LOWER > Day Rollovers

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ONE COMPONENT IS SUDDENLY LOWER > Day Rollovers > Month Rollovers

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ONE COMPONENT IS SUDDENLY LOWER > Day Rollovers > Month Rollovers > Year Rollovers

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OCCASIONAL WEIRDNESS

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OCCASIONAL WEIRDNESS > Leap Year Rollovers

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OCCASIONAL WEIRDNESS > Leap Year Rollovers > Years With Extra Months in Lunisolar Calendars

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OCCASIONAL WEIRDNESS > Leap Year Rollovers > Years With Extra Months in Lunisolar Calendars > Daylight Savings Time Rollovers

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THINGS I SCREWED UP EVEN AS I WROTE THIS TALK

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CALENDAR + DATECOMPONENTS Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)

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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..

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func formattedNextHoursAddingComponents(count: Int) -> [String] { var formattedHours = [String]() for hour in 0..

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func formattedNextHoursAddingComponents(count: Int) -> [String] { var formattedHours = [String]() for hour in 0..

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let now = Date() let nowAdjustingComponents = now .formattedNextHoursAdjustingComponents(count: 12) .joined(separator: "\n") let nowAddingComponents = now .formattedNextHoursAddingComponents(count: 12) .joined(separator: "\n")

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// 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")

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NOW

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ADJUSTING ADDING

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ADJUSTING ADDING ✅

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SPRING FORWARD

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ADJUSTING ADDING

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ADJUSTING ADDING

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ADJUSTING ADDING

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ADJUSTING ADDING

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ADJUSTING ADDING ❌

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CALENDAR + DATECOMPONENTS Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)

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CALENDAR + DATECOMPONENTS Calendar.autoupdatingCurrent.date(from dateComponents: DateComponents) Calendar.autoupdatingCurrent.date(byAdding dateComponents: DateComponents, to date: Date)

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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)

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March 9 2024 25:00

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March 9 2024 25:00 -> March 10 2024 01:00

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March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00

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March 9 2024 25:00 -> March 10 2024 01:00 -> March 10 2024 01:00 March 9 2024 26:00

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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 ->

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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?

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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

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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

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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

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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 ! .

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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)

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March 9 2024 17:00 + 8h

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March 9 2024 17:00 + 8h -> March 10 2024 01:00

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March 9 2024 17:00 + 8h -> March 10 2024 01:00 March 9 2024 17:00 + 9h

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March 9 2024 17:00 + 8h -> March 10 2024 01:00 March 9 2024 17:00 + 9h -> March 10 2024 03:00

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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

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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

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https://xkcd.com/2867/

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OBLIGATORY SUMMARY SLIDE

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OBLIGATORY SUMMARY SLIDE > Computers think about dates and time as numeric offsets from a specific point in time

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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

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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

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DONATION LINKS ! https://www.cnio.es/amigos- del-cnio/ ! https:// glioblastomafoundation.org/ get-involved/donate

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THANK YOU!

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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 > https://goshdarnformatstyle.com/ - A guide to SwiftUI FormatStyle funtimes

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LINKS: TIME EDITION > https://www.esa.int/Applications/ Satellite_navigation/Telling_time_on_the_Moon, the initial proposal the ESA made for coming up with a lunar time zone > https://www.smithsonianmag.com/smart-news/the- moon-will-get-its-own-time-zone-called-coordinated- lunar-time-under-nasas-lead-180984076/, a very readable summary of the effort that will be led by

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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