DateTimeException this interval is empty
or if the resulting interval would be invalid.
Example: -------------------- auto interval1 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1)); auto interval2 = Interval!Date(Date(1996, 1, 2), Date(2012, 3, 1));
interval1.expand(2); assert(interval1 == Interval!Date(Date(1994, 1, 2), Date(2014, 3, 1)));
interval2.expand(-2); assert(interval2 == Interval!Date(Date(1998, 1, 2), Date(2010, 3, 1))); --------------------