DateAndTime Offset Bug Proposal
Locked
12
12
Re: DateAndTime Offset Bug Proposal
 
|
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 <[hidden email]> 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 |
Re: DateAndTime Offset Bug Proposal
|
|
What is a field based date and time?
On Tue, Apr 10, 2018 at 1:32 PM, Esteban A. Maringolo <[hidden email]> 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 <[hidden email]> 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 > |
Re: DateAndTime Offset Bug Proposal
|
|
> On 10 Apr 2018, at 16:13, Stephane Ducasse <[hidden email]> wrote: > > What is a field based date and time? This is more of an implementation choice but it has probably influence on the API as well. Field based date/time/datetime objects are like the naive implementation where each element that we talk about as humans has its own instance variable. You would store hours, minutes, seconds, nanosecond separately, as well as year, month, day. This is not as efficient as the current implementations, where time is typically stored as seconds and nanoseconds, and dates as a single julian day number. Still, these are implementation choices. For example, the split between seconds and nanoseconds is a bit artificial as well (it is so that both remain SmallIntegers in 32-bit), while in 64-bit this decision could be revised. > On Tue, Apr 10, 2018 at 1:32 PM, Esteban A. Maringolo > <[hidden email]> 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 <[hidden email]> 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 >> > |
Re: DateAndTime Offset Bug Proposal
|
|
In reply to this post by Esteban A. Maringolo
> On 10 Apr 2018, at 13:32, Esteban A. Maringolo <[hidden email]> 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. Like Sean said elsewhere, the exist (much) better add-on frameworks, if you choose to use them, but they are optional. Right now, we are discussing what should be in the image by default. The current system is not bad at all, it just has deficiencies that could be improved upon. > An alternative would be to implement a "Calendar" (as in > Java.util.Calendar [1]), that can exist in parallel with the existing > Date class. I am not so sure that is a good example. > 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 <[hidden email]> 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 > |
Re: DateAndTime Offset Bug Proposal
|
|
In reply to this post by Stephane Ducasse-3
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. 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 > <[hidden email]> 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 <[hidden email]> 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 |
Re: DateAndTime Offset Bug Proposal
|
|
In reply to this post by Sven Van Caekenberghe-2
On 10/04/2018 11:37, Sven Van Caekenberghe wrote:
> Right now, we are discussing what should be in the image by default. > > The current system is not bad at all, it just has deficiencies that could be improved upon. > >> An alternative would be to implement a "Calendar" (as in >> Java.util.Calendar [1]), that can exist in parallel with the existing >> Date class. > > I am not so sure that is a good example. First time I new about Calendar I found it awkward (starting with the name). Years later I understood its purpose in comparison with a "point in time" Date or Timestamp. The name and implementation are TBD, but what I'm trying to exemplify is a particular case in a popular language. Regards! |
Re: DateAndTime Offset Bug Proposal
|
|
In reply to this post by Esteban A. Maringolo
> On 10 Apr 2018, at 16:46, Esteban A. Maringolo <[hidden email]> 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 >> <[hidden email]> 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 <[hidden email]> 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 > > > |
Re: DateAndTime Offset Bug Proposal
|
|
In reply to this post by Sven Van Caekenberghe-2
Hi Sven,
On Tue, Apr 10, 2018 at 7:33 AM, Sven Van Caekenberghe <[hidden email]> wrote:
Note that the VM provides times as either 64-bit LargePositiveInteger microseconds from 1901 (32-bits) or 61-bit positive SmallInteger microseconds from 1901 (64-bits), in either UTC or the current time zone. This gives us the following fit-for-purpose limits: DateAndTime fromSeconds: 1 << 64 - 1 // 1000000 586455-01-18T08:01:49-07:00 DateAndTime fromSeconds: SmallInteger maxVal // 1000000 38435-08-17T21:30:06-07:00 Choosing 64-bit nanoseconds doesn't work nearly as well; we run out of bits in 586 years. I don't buy the performance issue of keeping things as SmallIntegers. There is good 64-bit positive integer support in all the 32-bit VMs (e.g. in the interpreter, inlined #+. #- et al all work on a 64-bit integer range). If Pharo does decide to change the internal representation then I suggest that it uses the same representation as the VM.
_,,,^..^,,,_ best, Eliot |
«
Return to Pharo Smalltalk Developers
|
1 view|%1 views
| Free forum by Nabble | Edit this page |