[Pharo-project] Timespan #intersection: yields wrong result

Johan Brichau johan at inceptive.be
Tue May 3 19:25:47 CEST 2011


I traced a bug when working with timespans to the following issue illustrated in the code snippet below. 
The last expression in the snippet yields false, although it should yield true (imho).

	|start end span|
	start :=DateAndTime now.
	end := start + 1 hour.
	span := Timespan starting: start ending: end.
	(span intersection: span) = span  --> false

I think that the intersection of a span with itself, should be itself. The origin of the problem is that Timespan>>intersection: creates a new timespan roughly as follows:

	Timespan starting: aBegin ending: self end.

But Timespan>>end returns the end time of the timespan minus the clockprecision. As such, the intersecting span is a nanosecond shorter than the one we would expect. This eventually yields wrong results when working with timespans.

The real question now is: should the implementation of Timespan>>intersection be changed -or- should Timespan>>end really return the (non-included) end time (that was passed when constructing it)?

I sent this email to bugs at chronos-st.org, but a discussion here probably will not hurt either.

Best regards
Johan Brichau

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