So, Time and Dates are hard. When Date was a magnitude, it was easy. Now that it is a duration, it is occassionally wrong. Think about daylight savings time - at least one a year the day length is 25 hours, and once it is 23 hours (although in some places there are no Daylight Savings, so this isn't true, and in others, there are 2 switches, so it happens twice). Our current implementation doesn't take this into account - which is reasonable because it is hard to take this into account without a lot of work.

If we want to keep Date as a timespan (with rough correctness), maybe we could also add in Day (as a magnitude) to work like the old Date?

For what it is worth, I spend >80% of my time working with dates/timestamps, trying to turn them into Magnitudes for manipulations. The other 20%, I really enjoy them as timespans with locales since I deal with times from around the world. But the two uses are not quite easy to deal with - doable, just not quite intuitive.

-cbc

On Mon, Jun 27, 2016 at 3:41 AM, Bert Freudenberg <bert@freudenbergs.de> wrote:

On Mon, Jun 27, 2016 at 5:30 AM, David T. Lewis <lewis@mail.msen.com> wrote:
A bit off topic, but is is worth asking:
If we really want to model Date as a position on a continuum of date
values, and if we think that the implementation of Date as a kind of
Timespan is not right, then shouldn't we just consider going back to
the earlier (Squeak 3.6 and earlier) implementation of Date as a Magnitude,
rather than Date as a Timespan?

I think this is a very relevant question. We may have to distinguish a Day from a Date.

IMHO a birthday is a perfect example. It's defined by a day+month+year. If I was traveling I would celebrate the birthday in local time, so the generic "birthday" needs to compare equal to all the local dates independent of time zone.

This is how Dates worked before we made them Timespans (because they had no time, and hence no time zone). And this is also how they worked after I added the "nil" offset hack (which ignores the timezone). But it's a hack, not a good design. I'm not entirely sure what a good design would look like that also does not break old code.

- Bert -