# Set the type of a specific attribute.
	#
	# Parameters:
	#
	# * `index`: index of the attribute (zero-based).
	# * `attribute_type`: attribute's type.
	fun type_of=(index: Int, attribute_type: String) do
		assert index_in_bounds: index >= 0 and index < length
		data[index * 5 + 3] = attribute_type
	end