It's really the same problem extended to attributes of Data. The "immutability" in Data _also refers to the reference_. To take Python tuples (which are morall

It's really the same problem extended to attributes of Data. The "immutability" in Data _also refers to the reference_. To take Python tuples (which are morally pretty close to Data) my_data = ([],false) my_data[0].push(1) tuples are immutable, but this happens, because the "immutability" is in the same vein as JS's const: "we are always pointing to the same object".