Aside from the fact Java only released non-preview support for records one month ago, they:
- Don't support inheritance
- Can't be mutable
- Don't have a copy method
Copying objects is a well known need and there are countless libraries that try to help you with it. All with their own problems, notably runtime errors vs. compile time safety or pervasive use of reflection.
match msg with
| IncreaseCounter cnt ->
{ model with Count = model.Count + cnt }
| DecreaseCounter cnt ->
{ model with Count = model.Count - cnt }
| ResetCounter ->
{ model with Count = 0 }
| ChangeRubric name ->
{ model with Rubric = name, Count = 0 }
For the rest, I agree that in 99% of the cases inheritance and mutability are not needed if you're using greenfield Kotlin libraries. But they are unfortunately often necessary in the Java world.
Mutable data classes are especially quite useful for reducing boilerplate when creating classes that implement the Fluent Builder pattern, which is unfortunately quite necessary if you don't have a copy method...