Is it possible to inherit from a data class?

No. It's not an open class type and you can't define them to be

open

.

I see. Is there any discussion of making it easy to write your own data calsses such that you have say, a

User

and a

MutableUser

that inherits from User?

Why not just use mutable class? Even data class can be mutable

Side note: A data class, like a regular class, can be mutable, but you’d better better be very careful when their instances are put into a hash-list/set/collection…. 🙂

@gildor Sometimes it's just more convenient. Hard to say in general, without showing code.

You can define an interface that your

data class

implements. However, the

copy

function won’t be derivable from that interface….

I'm coming from C++ where you have

const

as a modifier, which is really fantastic.

The C++

const

. I like that, too. I wish, though, that

const

were the default and another keyword like

mutable

would have been used instead.

Yeah, I don't see good options. At it's most basic level, I'd like to be able to mutate a variable locally for convenience, but still have the guarantee that it is not mutated when passed into another function.

I have to say that I’m not a big fan of

MutableList

being a sub-interface of

List

.

ImmutableList

and

MutableList

should not have a parent-child hierarchy. If I have a

List

, it could be implemented by a mutable list, which means I cannot assume the

List

i have is actual immutable..

I have not, but I'm not sure I want to get into that level of complexity

There’s never a perfect solution! 🙂 Well, keeps our paychecks coming, I guess 😄

hah

Maybe if you start with this type of construct and go from there:

interface MyData {
    val id: Int
    val name: String
}

data class MutableMyData(
    override var id: Int,
    override var name: String
): MyData

Won’t get rid of the verbosity you try to avoid, though.

Yeah, I guess that would do it

Not being able to get teh

copy

function is the biggest trip-up. I wish there was a

data interface

of some sort

yeah.