What bothers me more is the lack of a way to ensure that the data is valid. Like always things look great in simple examples where it doesn't matter but fail wh

What bothers me more is the lack of a way to ensure that the data is valid. Like always things look great in simple examples where it doesn't matter but fail when it gets tricky. The main benefit of dedicated, encapsulated types is that they can preserve their invariants. Without that each function operating on "data" has to check that those invariants are kept. It's fine in trivial cases e.g. where this validation boils down to checking if a value is present or not - which might even be supported by the language. But I don't see this working in more complex cases. In my experience many (most?) bugs are caused by the implementation assuming something incorrect about the shape of the data and I feel like this principle only makes it more likely to happen.