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The point is that the local time would not change, even though the offset between UTC and local did change.

by wrs 3y ago

jvanderbot 3y ago
I see. The problem is there is no difference between local time and "offset from UTC", right?
- codetrotter 3y ago
  > there is no difference between local time and "offset from UTC" The difference is between applying the UTC offset for a future event using present rules. What we are saying is you should not do that because the rules can change. I ask you today that we meet at 3PM on January 24th in 2026, at the train station in Berlin. In my paper calendar book for I mark the date January 24th 2026 with the following note: “meet jvanderbot at 3PM at the train station in Berlin”. I carry this book with me for the next few years. Meanwhile, you decide to be modern so you store a note about the meeting in a database. In doing so, you convert the information into a UTC offset for that future time. But you are using current rules for today, which may change. And then when the day arrives, there has been political changes in the meantime that made it so that the utc offset is different. Because you converted to utc offset ahead of time, your representation of the time no longer maps to “3 PM” but instead to let’s say “4 PM”. I show up at 3 PM local time, as we had agreed. But you are nowhere to be seen because in your digital calendar the meeting appears to be for “4 PM”. This is what we mean when we are talking about the problem with converting a local time to a UTC offset a long time ahead.
- kelnos 3y ago
  Local time has no notion of a UTC offset. Local time is just "9am on August 31, 2024". It's up to the application's implementation details to pair it with a physical location (e.g. some lat/long in London). The app would then have to (as the event date approaches) resolve that into something more computer-clock-understandable; that is, it would have to say "this lat/long is located in timezone XYZ, which has offset ### for that date", so it could tell the OS's notification service to pop up reminders at the appropriate times.
scbrg 3y ago
As long as the invited people don't change nationality... https://www.972mag.com/the-worlds-only-ethnic-time-zone/ https://www.972mag.com/the-worlds-only-ethnic-time-zone/ If there's one thing I've learned about time keeping, it's that whenever you think you've got it all figured out, there's always one more corner case.

The point is that the local time would not change, even though the offset between UTC and local did change.

by wrs 3y ago

The point is that the local time would not change, even though the offset between UTC and local did change.

jvanderbot 3y ago

I see. The problem is there is no difference between local time and "offset from UTC", right?

codetrotter 3y ago
> there is no difference between local time and "offset from UTC" The difference is between applying the UTC offset for a future event using present rules. What we are saying is you should not do that because the rules can change. I ask you today that we meet at 3PM on January 24th in 2026, at the train station in Berlin. In my paper calendar book for I mark the date January 24th 2026 with the following note: “meet jvanderbot at 3PM at the train station in Berlin”. I carry this book with me for the next few years. Meanwhile, you decide to be modern so you store a note about the meeting in a database. In doing so, you convert the information into a UTC offset for that future time. But you are using current rules for today, which may change. And then when the day arrives, there has been political changes in the meantime that made it so that the utc offset is different. Because you converted to utc offset ahead of time, your representation of the time no longer maps to “3 PM” but instead to let’s say “4 PM”. I show up at 3 PM local time, as we had agreed. But you are nowhere to be seen because in your digital calendar the meeting appears to be for “4 PM”. This is what we mean when we are talking about the problem with converting a local time to a UTC offset a long time ahead.
kelnos 3y ago
Local time has no notion of a UTC offset. Local time is just "9am on August 31, 2024". It's up to the application's implementation details to pair it with a physical location (e.g. some lat/long in London). The app would then have to (as the event date approaches) resolve that into something more computer-clock-understandable; that is, it would have to say "this lat/long is located in timezone XYZ, which has offset ### for that date", so it could tell the OS's notification service to pop up reminders at the appropriate times.

scbrg 3y ago

As long as the invited people don't change nationality... https://www.972mag.com/the-worlds-only-ethnic-time-zone/ https://www.972mag.com/the-worlds-only-ethnic-time-zone/ If there's one thing I've learned about time keeping, it's that whenever you think you've got it all figured out, there's always one more corner case.