On 30 Oct 2009, at 21:09, Scott Bailey wrote:
My personal feeling is that when you provide any ordering operator
and
negation you can easily provide an absolute value operator. We've
already (somewhat arbitrarily) decided that one of '1month -30days'
and
'-1month 30days) is "greater" than the other, so why not provide an
operator that returns the "greater" of an interval value and its own
negation?
Technically, greater doesn't arbitrarily decide one is greater than
the other. It determines the two are equivalent and (correctly)
chooses the leftmost one.
I think it is important to separate the concept of an interval with
addition of an interval with a timestamp. By (the interval type's)
definition a day is 24 hours, a month is 30 days, a year is 365.25
days. And the user needs to understand that abs and extract epoch do
their calculations based on those definitions rather than what would
happen when applied to an arbitrary timestamp.
There's a slight complication to this approach; what happens if you
ask for <timestamp> + abs(<interval>)?
You don't want to calculate the result of abs() based on a 24h day, a
30d month and a 365.25d year as there is a timestamp to base your
calculations on, but AFAIK you can't see that from within the abs()
function implementation. Unless you store that information in the
context somehow.
Alban Hertroys
--
If you can't see the forest for the trees,
cut the trees and you'll see there is no forest.
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