Re: [Boost-users] [date_time] time_periodS subtraction

From: Zeljko Vrba (zvrba_at_[hidden])
Date: 2008-05-18 10:24:51

On Sun, May 18, 2008 at 04:17:41PM +0300, Igor R. wrote:
>
> Why is subtraction of periods less "specific to the date_time library", than the following functions?
> contains(), intersects(), intersection(), shift(), expand(), merge(), span()
>
Ugh, it's not; I wasn't aware that they were already included in the library.
They are all good candidates for generalization and placement in a separate
library/class. IMHO.

>  
> Subtraction of intervals seems to be very "native" operation for time_period, since it's VERY common task when working with time intervals.
>  
I'm the wrong person to complain to.  The class seems generally unable to
represent non-convex sets, e.g. the documentation for the "merge" method
says: "Returns union of two periods. Null if no intersection."  So the
union of disjoint intervals [2,3] and [4,5] will return null.  (Yes, it's
still possible to write a difference operator crippled[*] in the same way
as the merge operator.  Hence the suggestion for factoring into a separate
general-purpose library.)

[*] Conditionally speaking crippled.  Period is explicitly defined as
"[.. range] between two times", something that the set [2,3] U [4,5]
most definitely is not.  I.e. I'd say you're using the wrong tool for
the job.