> On 10 Apr 2018, at 16:46, Esteban A. Maringolo <emaring...@gmail.com> wrote: > > This a recurring topic in the mailing list. > > See: > http://forum.world.st/Interesting-Date-Time-Thread-on-Squeak-Dev-td4778652.html#a4778970 > > Or directly go to this https://www.w3.org/TR/timezone/ > > Pharo's Date and Time classes are incremental/offset based, whereas a > field based Date behaves more as "expected" in terms of adding > days/months/days/hours/etc.
That is not really true (that it depends on the internal representation). Any date/time/datetime object needs API/behaviour that allows accessing and manipulation in human terms. How this is implemented is up to the implementation (duh). Having separate year/month/day fields does not at all shield you from the fact that 'adding a day to jan 27' is different to 'adding a day to feb 27', of 'dec 31' - the implementation has to make sure that all this works correctly (and this is often pretty complex, needing to take many aspects into account). Having separate fields suggest this is easy, but that is a delusion. Anyway, I am pretty sure you understand. And about Java's Calendar, I know that it is an object that manipulates other objects, it just has a pretty ugly interface, and does not feel very OO like. I hear many people curse it, but it probably does its job. > The internal implementation might vary and there are going to be > tradeoffs, but IMO for scheduling solutions calendar based are better > suited. > > Regards! > > > On 10/04/2018 11:13, Stephane Ducasse wrote: >> What is a field based date and time? >> >> On Tue, Apr 10, 2018 at 1:32 PM, Esteban A. Maringolo >> <emaring...@gmail.com> wrote: >>> What is missing in the current Pharo image is a field based >>> Date/DateTime instead of an offset+duration one as it currently is. >>> >>> Why not use Chronos instead? AFAIR Chronos provides that. >>> >>> An alternative would be to implement a "Calendar" (as in >>> Java.util.Calendar [1]), that can exist in parallel with the existing >>> Date class. >>> >>> Regards, >>> >>> [1] https://developer.android.com/reference/java/util/Calendar.html >>> >>> On 10/04/2018 03:30, Stephane Ducasse wrote: >>>> Hi Paul >>>> >>>> I agree and instead of patching the current system I would start using >>>> TDD to design >>>> a new Date package. >>>> >>>> stef >>>> >>>> On Mon, Apr 9, 2018 at 8:42 PM, Paul DeBruicker <pdebr...@gmail.com> wrote: >>>>> I think #= is a bad selector for Date and should be avoided when >>>>> determining >>>>> whether something happens on a date, or whether two dates are the same. >>>>> We >>>>> all know March 24th in London covers a different 24 hours than March 24th >>>>> in >>>>> Hawaii but Date>>#= does not. >>>>> >>>>> >>>>> >>>>> I think whats needed are more descriptive selectors like >>>>> >>>>> >>>>> Date>>#isSameOnDateAs: aDateOrDateAndTime >>>>> Date>>#overlapsWithDate: aDate >>>>> DateAndTime>>#occursOnDate: aDate >>>>> DateAndTime>>#sameHMSButDifferentUTCIn: aTimeZoneKey >>>>> DateAndTime>>#sameUTCButDifferentHMSIn: aTimeZoneKey >>>>> >>>>> and change Date>>#= to #shouldNotImplement. >>>>> >>>>> >>>>> FWIW I also don't like #offset: as before you send it you know the >>>>> timezone >>>>> and after you may let that knowledge be forgotten. Real offsets can change >>>>> as laws change. >>>>> >>>>> >>>>> >>>>> I think people are aware of this but if you have need for comparing dates >>>>> & >>>>> times then you must use a library that accesses the regularly updated >>>>> Olson >>>>> timezone database on your system and classes that respect time zones. >>>>> Time >>>>> zones are political, and legal definitions of offsets can change hours >>>>> before the DST transition dates & times. >>>>> >>>>> >>>>> I don't think it matters which default timezone you pick for the image if >>>>> you're not going to take them into account when doing comparisons. >>>>> >>>>> >>>>> Unfortunately there isn't a way to avoid this complexity until DST goes >>>>> away. >>>>> >>>>> >>>>> There's certainly flaws to how we currently do it and I think >>>>> TimeZoneDatabase and Chronos make good attempts to fix it. I haven't >>>>> looked >>>>> at Chalten but would guess its good too. >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> Sean P. DeNigris wrote >>>>>> I was bitten by this very annoying bug again. As most of us probably know >>>>>> due >>>>>> to the steady stream of confused ML posts in the past, the bug in summary >>>>>> is >>>>>> that we have an incomplete timezone implementation that doesn't properly >>>>>> take into account historical DST changes. This flares up without warning >>>>>> especially when DST toggles. I created a wiki page to document the >>>>>> situation: https://github.com/seandenigris/pharo/wiki/Time-Zone-Fiasco >>>>>> >>>>>> Here's an example blowup: at 11:59pm before DST changes, eval aDate := >>>>>> '1/1/1901' asDate. Now, wait two minutes and at 12:01am eval self assert: >>>>>> '1/1/1901' asDate = aDate and… whammo, an exception! The "different" >>>>>> offsets >>>>>> render equal dates unequal depending on when the objects were created. >>>>>> >>>>>> The more I think about it, the more I think that we should just assume >>>>>> UTC >>>>>> for all Date[AndTime]s that don't explicitly specify an offset, rather >>>>>> than >>>>>> pretend to set an offset which is only sometimes correct. More advanced >>>>>> users can use one of the available libraries to get full timezone >>>>>> support. >>>>>> What do you think? >>>>>> >>>>>> >>>>>> >>>>>> ----- >>>>>> Cheers, >>>>>> Sean >>>>>> -- >>>>>> Sent from: http://forum.world.st/Pharo-Smalltalk-Developers-f1294837.html >>>>> >>>>> >>>>> >>>>> >>>>> -- >>>>> Sent from: http://forum.world.st/Pharo-Smalltalk-Developers-f1294837.html >>>>> >>> -- >>> Esteban A. Maringolo >>> > > -- > Esteban A. Maringolo > > >
