[lolinder]

This is exactly the same problem that OP was drawing out with Ruby's Data: the references inside the Data object are immutable and cannot be changed to point to other objects, but once you've dereferenced the (immutable) pointers there are no immutability guarantees. Hence, shallow immutability.

The only conceptual difference between this and JS's `const` is that you can't use `const` to declare object properties immutable; for that you need Object.freeze().