[tz] NetBSD vs Darwin timezone API

[Lester Caine]

On 11/11/16 01:12, Guy Harris wrote:
> 1) is a timezone object immutable across changes to *the time zone data files*?

Ignoring the full update to the tzdata set for a moment. This was one of
the KEY elements for tzdist. A call to tzdist would flag that there was
a change to an offset it MAY affect the time object one is looking at.
The whole point of that discussion was that one potentially has no idea
if the time actually needs to change. If the event being calendared is
at a fixed UTC time ... a video link slot to another timezone ... then
the time is 'immutable' ( why not just say fixed! ) so one has to change
the local time, but if the local time is fixed, the other calenders need
updating instead.

Original discussions on tzdist were based on the assumption that tzdist
simply provided the CURRENT offsets, but one HAS to keep the tz version
as a key element of any time object. This is where genealogical data
that was normalized in the past has become corrupt simply because the
tzdata set used to normalize it was not recorded. One needs more than
just the 'current' tzdata, one needs a means of establishing that ...
having got a set of data which was encoded using one tz version, one can
if necessary update it to another for comparison. But this STILL fails
if the event is fixed to local time rather than UTC time such as flagged
by astronomical events that can make a DST change dependent on real
observations.

Basically we are stuffed on some events what ever we do ...

-- 
Lester Caine - G8HFL
-----------------------------
Contact - http://lsces.co.uk/wiki/?page=contact
L.S.Caine Electronic Services - http://lsces.co.uk
EnquirySolve - http://enquirysolve.com/
Model Engineers Digital Workshop - http://medw.co.uk
Rainbow Digital Media - http://rainbowdigitalmedia.co.uk