(cross posting to squeak-dev) On Wed, May 16, 2012 at 01:50:16PM -0700, Sean P. DeNigris wrote:
David T. Lewis wrote
So no, it is not a constant.
Let me rephrase: wouldn't it be better if it was a constant, like dos and unix?
Yes it would be better if the Smalltalk epoch was an unambiguously defined value, but unfortunately it is not. That is the reason that the clearly defined Posix epoch would be a more suitable basis for these calculations. <ot> Funny that you should mention DOS. DOS has exactly the same problem as Squeak/Pharo in this regard. It was originally designed as a simple single-user system, where the user was expected to set the clock properly on all of his/her alarm clocks, kitchen appliances, and computers. It has no knowledge of time zones or daylight savings time, and this leads to all sorts of bugs in applications running on MS-DOS that assume that the system time is correct. I was dealing with a real-life bug of this sort last week that had people spending huge amounts of time and energy trying to figure out what was causing clocks to be "reset" in a complex multi-platform application that happened to include some old DOS based computers that were sending time stamped messages. </ot>
I find the current behavior confusing e.g.
dt := '1/15/2012 0000+00:00' asDateAndTime.
DateAndTime localTimeZone: (TimeZone timeZones detect: [ :e | e abbreviation = 'PDT' ]). s := dt asSeconds. "3504013200"
"Now I move to Greenwich" DateAndTime localTimeZone: (TimeZone timeZones detect: [ :e | e abbreviation = 'UTC' ]). DateAndTime fromSeconds: s. "2012-01-14T17:00:00+00:00" "Oops!"
Yes, that looks broken to me too. But DateAndTime class>>fromSeconds: is documented as "Answer a DateAndTime since the Squeak epoch: 1 January 1901" which by definition cannot be correctly implemented. One solution would be to gain agreement among all flavors of Smalltalk as to the proper definition of the Smalltalk epoch. But it seems to me that it would be vastly simpler to just use a definition that is already agreed and documented (i.e. Posix epoch), and leave the "Smalltalk epoch" behind as an interesting historical artifact. Dave