My intuition tells me that hiding data in objects does not really help as long as the data is still mutable. Immutability is the only way to guarantee true enca

My intuition tells me that hiding data in objects does not really help as long as the data is still mutable. Immutability is the only way to guarantee true encapsulation for objects that don't actually represent something inherently stateful. (eg. file on disk) Coupling data and operations is also a problem. It's non-extensible, both in that you can't add more data and use the same operations, and you can't add more operations that work on the added data. Inheritance works around some of this, but it doesn't solve the general problem. What if it makes sense to add the same piece of data to objects of classes from different parts of the hierarchy? The thing about functions is that you can always write a new one that works with anything you want. You don't need to add it to a class or an interface (you can, if the language allows that), and if possible, with immutable data that essentially makes the function a unit of perfect encapsulation.