Returns a Duration with the difference between this and other.
DateTime berlinWallFell = new DateTime(1989, DateTime.NOVEMBER, 9);
DateTime dDay = new DateTime(1944, DateTime.JUNE, 6);
Duration difference = berlinWallFell.difference(dDay);
assert(difference.inDays == 16592);
Source
Duration difference(DateTime other) {
int ms = millisecondsSinceEpoch;
int otherMs = other.millisecondsSinceEpoch;
return new Duration(milliseconds: ms - otherMs);
}