Extended ranges required for dates and date-times

[Jason Harris]

Hello,

As the maintainer of the ExtDate* classes, I'm glad to see that we are 
considering adopting them in kdelibs.  I had proposed this back when 
KDateTime was first proposed, but the consensus at that time was that 
not enough apps would need extended dates to make it worthwhile.

There is a test program in libkdeedu/extdate/tests that demonstrates 
that ExtDate and QDate behave identically for the range of dates over 
which QDate is valid, so I think there's little reason to use QDate 
internally for non-extended dates.

Another issue brought up is the "slightly bizarre" date range of -50000 
to +50000.  This was an essentially arbitrary choice; there's no reason 
why the date range could not be made wider (or narrower).

One issue that has not been mentioned: what is to be done for calendar 
dates prior to 1752, for which identifying a particular calendar date 
becomes ambiguous (due to different calendar systems in use prior to 
1752)?  We handle this very simply in ExtDate: we totally ignore it, and 
simply extrapolate the modern Gregorian calendar backward.  Thus ancient 
dates in ExtDate are not *historically* accurate, but they are more 
*seasonally* accurate (which was more important for us in KStars).

regards,
Jason