Function std.datetime.interval.IntervalRange.popFront
Pops front from the range, using func to generate the next
time point in the range. If the generated time point is beyond the edge
of the range, then front is set to that edge, and the range is then
empty. So, if iterating forwards, and the generated time point is
greater than the interval's end, then front is set to
end. If iterating backwards, and the generated time point is less
than the interval's begin, then front is set to begin.
void popFront();
Throws
DateTimeException if the range is empty
or if the generated time point is in the wrong direction (i.e. if
iterating forward and the generated time point is before front,
or if iterating backwards and the generated time point is after
front).