Cython handling of 0-length arrays feels awkward

[ajfriend]

See: #99 (comment)

[ajfriend]

h3-py/src/h3/_cy/cells.pyx

Lines 178 to 197 in 72db3f7

	cpdef H3int[:] compact(const H3int[:] hu):
	# todo: the Clib can handle 0-len arrays because it **avoids**
	# dereferencing the pointer, but Cython's syntax of
	# `&hu[0]` **requires** a dereference. For Cython, checking for array
	# length of zero and returning early seems like the easiest solution.
	# note: open to better ideas!
	if len(hu) == 0:
	return empty_memory_view()
	for h in hu: ## todo: should we have an array version? would that be faster?
	check_cell(h)
	ptr = create_ptr(len(hu))
	flag = h3lib.compact(&hu[0], ptr, len(hu))
	mv = create_mv(ptr, len(hu))
	if flag != 0:
	raise H3ValueError('Could not compact set of hexagons!')
	return mv