On Apr 27, 2013, at 6:33 PM, Nicolas Cellier
<nicolas.cellier.aka.n...@gmail.com> wrote:
> Since DateAndTime comment is out of date (sic !) and current implementation
> seems not free of bug, here is an effort to summarize and understand the
> whole thing, let's call this a review.
Thanks this is a great initiative!
> Please tell me where my interpretations are wrong.
>
> 1) The DateAndTime is stored internally as
> - a point in UTC time (julianDayNumber, seconds, nanos)
> - an offset from UTC (a Duration) denoting the local time zone
>
> 2) The ticks method returns the UTC part {julianDayNumber. seconds. nanos}
>
> 3) DateAndTime print themselves in local time using the offset
>
> 4) other methods (with some exceptions) return the local dateAndTime parts
> (year month day hours minutes seconds)
>
> Exceptions are:
> - secondsSinceMidnight (which should be renamed secondsSinceMidnightUTC IMO,
> even if the method is classified private)
> - julianDayNumberUTC as the name tells
>
> So far so good (but secondsSinceMidnight which is error prone)
>
> What I find strange:
> - #hash uses the offset... Why ???
>
> d1 := DateAndTime now.
> d2 := d1 offset: d1 offset + 1 hours.
> {
> d1 = d2.
> d1 hash = d2 hash.
> }
> gives #(true false), a clue?
>
> - #< compares julianDayNumber (the UTC inst. var.) with otherDate
> julianDayNumber (with otherDate local offset) which seems wrong, it should
> better use julianDayNumberUTC or (normalized) ticks.
>
> - #= could be simplified and accelerated if using #hasEqualTicks: (if the
> ticks are correctly normalized though which would be the case since
> #ticks:offset: does, unfortunately #setJdn:seconds:nanos:offset: does not).
>
> Some senders of #setJdn:seconds:nanos:offset: don't normalize the
> day/seconds/nanos, though it should be their responsibility (DateAndTime
> todayAtMilliSeconds: xxx) (DateAndTime todayAtNanoSeconds: xxx), not counting
> year:month:day:hour:minute:second:nanoSecond:offset: which does not either
> (many senders...).
> Maybe we should better let the normalization responsibility to
> #setJdn:seconds:nanos:offset:.
>
> It remain to analyze the conversion protocol (asYear etc...) which seems to
> use the local time year, but I don't understand the whole Timespan thing
> right now (why DateAndTime now asYear starts now, and not on january 1st?).
>
> Nicolas
>
>
