Even "Date today" and "Date now" is created by DateAndTime.
So, due to the DateAndTime internals, one can't persist Date instance (eg. with
Fuel) and use it as exact "date/day value" for comparisons later in time (when
GST changes back and forth).
The same date value (one created before DST change, one created after DST
change) will be different even in long run (on the DST change day - Date today
in created on 1:00am will be different from Date today created on 2:00 am -
weird! it's the same day!). Isn't the usage of "time" component in Date class a
bug (at least in comparison #= method)?
What about to redefine #= instance method in Date class (it's defined in
Timespan super class now)?
= comparand
^ self species = comparand species
and: [ self translateToUTC = comparand translateToUTC ].
Opinions?
pf
> Date>>year:month:day: (respectively Date>>#starting:) is using DateAndTime to
> specify the start, and DateAndTime will of course differ.
>
> To me it seems like someone was reusing implementation; because Date normally
> shouldn't have/care about time information, and yet it subclasses from
> Timespan class, which has/cares about time information. So the Date is
> actually encoded in Timespan's 'starting' instVar as DateAndTime instance,
> which is obviously breaking if TimeZone is applied.
>
> Maybe a fix (apart from not using Time in Date) would be to make sure Date's
> methods use DateAndTime offset to 0?
> Because even without daylight saving, if you create a Date instance in one
> country, and move to different TZ it should break; so always keeping it UTC/0
> would make sense to me.
>
> Peter
>
> On Sun, Mar 26, 2017 at 10:17:14AM +0200, Petr Fischer wrote:
> > Hello,
> >
> > 1) when I create date on: 2017/03/20 (before Daylight Saving Time change)
> > with this code:
> >
> > D1 := Date year: 2017 month: 3 day: 26.
> >
> > Date object is created with instvars:
> > start: 2017-03-26T00:00:00+01:00
> > duration: 1:00:00:00
> >
> > 2) when I create same Date instance with the same code on/after: 2017/03/26
> > (after Daylight Saving Time change):
> >
> > D2 := Date year: 2017 month: 3 day: 26.
> >
> > Date instance with this instvars returned:
> > start: 2017-03-26T00:00:00+02:00
> > duration: 1:00:00:00
> >
> > 3) D1 != D2
> >
> > So, for example: persisted instance of date (Date year: 2017 month: 3 day:
> > 26) created before DST change is not equal with date instance (Date year:
> > 2017 month: 3 day: 26) created after DST change.
> > DST change breaks equality of the same date :(
> >
> > Is it OK?
> >
> > Thanks! Petr Fischer
> >
>
