Re: [MacPerl-Porters] MacPerl daylight saving time issue

On Wednesday, September 18, 2002, at 12:38 AM, Peter Prymmer wrote:
> Actually I do not think that your Christmas Eve example was bad. Yes
> daylight savings time rules may be complicated but it "should not"  be
> impossible to code around

Not impossible, but rather hard. At some point, it also would become a 
question of how much code to add to a general purpose library just to 
handle a special case which is not handled on many commercial platforms 
either.

> (I say that as someone who has never attempted
> to modify GUSI).  I note that for the "Date & Time" control panel 
> version
> 8.3 that ships with Mac OS 9.1 there is a checkbox for "Set
> Daylight-Saving Time Automatically", from which I conclude that parts 
> of
> the system do know what time zone the Mac is in

Yes.

>  and what the DST -> standard time -> DST calendar rules are.

Hmm, I can't check this from X, but doesn't the "Automatically" here 
refer to getting the flag from a network time server? AFAIK, the last 
time I checked, the three DST options available were:

  - Click the checkbox yourself in spring and fall. This is obviously 
unsuited to calculating future dates.
  - Specify the switchover rules (2nd saturday in march) appropriate to 
your location. This
    would work, but there is no API to the rules.
  - Get the DST setting from a network time server. This is also 
unsuited to calculating any DST setting except for the present.

Matthias