# Returns an empty `U16String` of capacity `cap` or a NULL `U16String` if no `cap` parameter is provided.
	# The `cap` argument is the number of code units (aka UTF-16 encoded characters or `UChar`) allocated to `uchar_string`.
	# If the number of code units is known in advance, it can be provided with the `units` parameter.
	init (cap: nullable Int, units: nullable Int) do
		if cap == null then
			uchar_string = new UCharString.nul
		else
			assert cap >= 0

			if not units == null then
				assert units <= cap
				code_units = units
			end

			uchar_string = new UCharString.empty(cap)
			capacity = cap
		end
	end