I'm sure a use case exists where you want to store a timezone, but I don't know what it is. I try and use UTC everywhere, and only worry about time zones when displaying.
Any future event (such as a meeting) can't be stored as UTC, because time zone rules may change between now and the event date, but the event still needs to happen 10am local time.
I don't think that's necessarily true. If you really care about that edge case, then you would need to ask whether the local time should change if the local time zone's UTC unpredictably changes. I don't think you can make a safe assumption either way.
How often do time zone rules change? That seems like a fairly rare event. If you're talking about daylight savings time, the date library you're using to convert local time to UTC should account for that.
There's always changes happening. Just this year, Southern Chile changed its summer time zone offset, Haiti started observing DST and Mongolia stopped doing that.
It doesnt have to be rules, time zones have relative and changing references against UTC, for example daylight saving time which is 2x per year in the US.
If you schedule a meeting for 4pm Tuesday next week, but DST happens Friday this week, you still want the meeting on 4pm Tuesday next week. The local timezone and local timestamp is necessary for that.
If the software converts to UTC it should be using the expected local timezone on the target date (4pm Tuesday), not the current timezone. So this will only be a problem if the TZ tables for the future are not correct (which happens, as noted in sibling comments, but is not as widespread as every DST event like your comment seems to imply).
That doesn't sound right. If you have a local timestamp with the date and the time and convert it to UTC, shouldn't the datetime library look up the rules for this timezone and convert it correctly? Isn't that the whole point of having timezones be more than offsets?
It doesn't "break"; yes, you have to change the local time for the other time zones, but the point is that some times you have to use a specific reference time zone, so you got to save it.
No, appointments for participants from multiple time zones are not specified in implicit local time, but rather in a some explicit timezone, often UTC, so you have to store that timezone instead of the implicit local one.
Aren't timezones an offset of UTC by definition? I thought during daylight savings time a country is temporarily changing their timezone. Isn't that why we have EST and EDT: they're two different timezones?
No, time zones are a specific geo region that follows a certain time standard. The standard has a relative reference to UTC but that reference may change, either regularly or randomly.
Eastern Time Zone is a single time zone, that has different offsets depending on season, formally referred to as EDT and EST to make it easier to identify as daylight or standard references to UTC.
Even regions within the same time zone don't follow the standard exactly, so Panama does not observe daylight saving time while New York does. This is why we have even more granular settings used for calendars and dates.
Timezones have more information and are a mini-database in themselves, which is why most database include the information and have timezone capable types. Offsets as simple numbers are not usable in any real calculation.
100% of apps? You must not know what timezone intricacies are then or just how much effort is spent to make sure time itself is properly handled, especially in any major application that has global users.
>You must not know what timezone intricacies are then or just how much effort is spent to make sure time itself is properly handled, especially in any major application that has global users.