4 ms·

I think it's close. As the article explains, though, present and past timestamps can be impacted too - your timezone library may be out of date at the moment y

I think it's close. As the article explains, though, present and past timestamps can be impacted too - your timezone library may be out of date at the moment you save the timestamp, or in some cases the legal body defining the timezone may reach into the past with a timezone change.

jrochkind1 8y ago
How can a legal body possibly change the timezone retroactively? All those people on Monday that _thought_ it was 1pm, it turns on Tuesday we decided it was actually 2pm when they thought it was 1pm. But nobody could have known that on Monday. So they've got to... go back and change any times they put on documents on Monday? How does that make any sense? But incorrect timezone data or implementation is too real, true.
- NateEag 8y ago
  Governments can do what they like, by and large. Just because it's crazy doesn't mean they won't, and nothing about physical reality prevents them from doing this. I'm not aware of any specific examples, so perhaps I'm being too paranoid in my first post, but it would not surprise me in the least to hear of, for example, a bill to eliminate DST in a state that somehow manages not to pass until a day or three after the DST change takes effect. There have at least been some some bizarre calendar changes that many software systems fail to accommodate, which probably feeds into my above paranoia: https://en.m.wikipedia.org/wiki/Soviet_calendar https://en.m.wikipedia.org/wiki/Soviet_calendar https://mentalfloss.com/article/51370/why-our-calendars-skipped-11-days-1752 https://mentalfloss.com/article/51370/why-our-calendars-skip...
- NateEag 8y ago
  I should also clarify that conceptually, even if you keep your copy of the tzinfo database obsessively up-to-date, you could still experience what appear to be retroactive updates, per the "Theory and Pragmatics" document from the tzinfo project [1]. That's because some governments are pretty sloppy about announcing their timezone changes in advance. It's compounded by the tzinfo DB being maintained by volunteers (who can't spend their lives obsessively gathering timezone change announcements the instant they're made), and the lead time necessary for software projects to update their tzinfo instances [2]. So, while retroactive changes may not be consciously made often or ever, it's certainly an effect that happens in practice. 1: https://data.iana.org/time-zones/theory.html#accuracy https://data.iana.org/time-zones/theory.html#accuracy 2: https://codeofmatt.com/on-the-timing-of-time-zone-changes/ https://codeofmatt.com/on-the-timing-of-time-zone-changes/
  - jrochkind1 8y ago
    Ah, good point! With reference links, thanks!

jrochkind1 8y ago

How can a legal body possibly change the timezone retroactively? All those people on Monday that _thought_ it was 1pm, it turns on Tuesday we decided it was actually 2pm when they thought it was 1pm. But nobody could have known that on Monday. So they've got to... go back and change any times they put on documents on Monday? How does that make any sense? But incorrect timezone data or implementation is too real, true.

NateEag 8y ago
Governments can do what they like, by and large. Just because it's crazy doesn't mean they won't, and nothing about physical reality prevents them from doing this. I'm not aware of any specific examples, so perhaps I'm being too paranoid in my first post, but it would not surprise me in the least to hear of, for example, a bill to eliminate DST in a state that somehow manages not to pass until a day or three after the DST change takes effect. There have at least been some some bizarre calendar changes that many software systems fail to accommodate, which probably feeds into my above paranoia: https://en.m.wikipedia.org/wiki/Soviet_calendar https://en.m.wikipedia.org/wiki/Soviet_calendar https://mentalfloss.com/article/51370/why-our-calendars-skipped-11-days-1752 https://mentalfloss.com/article/51370/why-our-calendars-skip...
NateEag 8y ago
I should also clarify that conceptually, even if you keep your copy of the tzinfo database obsessively up-to-date, you could still experience what appear to be retroactive updates, per the "Theory and Pragmatics" document from the tzinfo project [1]. That's because some governments are pretty sloppy about announcing their timezone changes in advance. It's compounded by the tzinfo DB being maintained by volunteers (who can't spend their lives obsessively gathering timezone change announcements the instant they're made), and the lead time necessary for software projects to update their tzinfo instances [2]. So, while retroactive changes may not be consciously made often or ever, it's certainly an effect that happens in practice. 1: https://data.iana.org/time-zones/theory.html#accuracy https://data.iana.org/time-zones/theory.html#accuracy 2: https://codeofmatt.com/on-the-timing-of-time-zone-changes/ https://codeofmatt.com/on-the-timing-of-time-zone-changes/
- jrochkind1 8y ago
  Ah, good point! With reference links, thanks!