Chat about edge cases 20070719
Yoshito Umaoka <firstname.lastname@example.org>
Thu, Jul 19, 2007 at 3:26 PM
Yoshito: Not sure I'm understanding what you are talking about - getOffset()
My point is - time overlap could happen standard -> standard
dayligh -> daylight
me: hm, i had thought that we were talking about the same thing...
me: let's assume DST ends on november 5. so on nov05 until 02:00 we have DST, but then we "fall back" to 01:00 std time.
Yoshito: I understand the case.
I'm talking about -
standard offset change -
me: now with getOffset(UDate=nov05 01:30, local) i want to specify whether it's the earlier (DST) or the later (std) point in time
Yoshito: both before/after are standard time.
me: yes, before nov05 01:00 it's DST, and after nov05 02:00 it's std time
Yoshito: this is rare case.. but I think there are some examples.
Yoshito: no no... I meant
for example, a country decided to change standard time from UTC+4:00 to UTC+5:00
no DST is involved
but - overlap happens.
oops.. my example is wrong.. I meant UTC+5:00 to UTC+4:00
or like the counties in Indiana which are changing between Central and Eastern time several times in a row
you are right, there could be ambiguities there, too
Yoshito: so.. what you want to specify is either time before transition is used or time after the transition is used when ambigious case.
1st or 2nd iteration
usually DST -> STD
but, STD -> STD
DST -> DST
me: now i get it. same parameter, but with expanded semantics
and named to express those
Yoshito: ok.. now we are on the smae page :)
Anyway, the idea is great - we need a way to allow user to controll the behavior of ambigious local time.
me: would you like to reply again and clarify, or would you like me to explain to the list?
Yoshito: At least for ICU4J, I believe the API is public and stable.. so need a new API.
I will send my note for clarifying this.
me: absolutely. in icu4c as well, getOffset() is @stable ICU 2.8
i wasn't intending to propose to change an existing function
it could be a new overload, or more explicitly
getOffsetFromLocal(UDate date, UBool earlierTimeIfOverlap, ...)
Yoshito: yeah, something like that.
me: thanks for being persistent in clarifying! :-)
Yoshito: I think we do not need to worry about more than 2 iteration..
I believe it have never happened in actual time zones.
me: right. that would require a time zone changing offsets more than once a day.
more than once within an hour, actually