(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