[LEAPSECS] Late binding, was Re: Lets get REAL about time.

[Tony Finch]

Rob Seaman <seaman at noao.edu> wrote:

>

> The plight will be writ large should the notion of timezone roulette be

> implemented.  In that case, over the centuries it will be similarly

> unpredictable what timezone a particular country or province, state or

> city observes - will observe - or did observe at some past moment

> (without consulting some big book of timekeeping trivia).  What is a

> curiosity currently, the adjustment of a timezone, would become

> commonplace and historians won't be able to "do operations" on UTC

> timezone offsets as Zefram noted:


It is already commonplace.

The only sure way to schedule an event in the future is to specify a time
and a place, and the time is to be understood as the commonly understood
local time at that place. You also need a disambiguation flag to deal with
changes to the local time scale, which should indicate the earlier or
later of the possible times, so it can accommodate multi-stage DST or date
line switches or other oddities not covered by a DST flag. In some cases
you might need an abstruse notion of place, e.g. Han Xinjiang vs. Uighur
Xinjiang.

Calendaring software gets this wrong, and embeds the TZ offset in the data
for a scheduled event too early.

Warner said:


> We need some kind of 'late binding' so that we can have time that's in

> July 2012 when called from an app in Dec 2011 that shifts 1s once

> the leap tables are updated...


You achieve late binding by representing the target time in the target
timescale. If you translate to some other timescale that has an
unpredictable relation to the target timescale, you are causing problems
for yourself.

Poul-Henning said:


> All other timescales, including UTC, will be derived from this floating

> point value and represented in a suitable form for that timescale. All

> other timescales, including UTC, will be derived from this floating

> point value and represented in a suitable form for that timescale.


Exactly.

Tony.
-- 
f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
Fair Isle, Faeroes: Cyclonic, becoming southerly or southeasterly later, 5 to
7, occasionally gale 8 at first in north Faeroes, becoming variable 4 for a
time. Moderate or rough, occasionally very rough at first in north Faeroes.
Wintry showers. Good, occasionally poor.