I want to extend a data class. ``` data class Hog...

# getting-started

[atsushi-koshikizawa]

I want to extend a data class.

data class Hoge(val foo: String, val bar: String)

data class Fuga(foo: String, bar: String, val buz: String) : Hoge(foo, bar) // compile error

Data class in Kotlin cannot be opened, and its primary constructor must have only property parameters.

I have two questions.

1. Why cannot data classes be opened?
2. How can I reuse Hoge class to define Fuga class?

[Matthieu Esnault]

You might be interested by the info here: https://stackoverflow.com/questions/26444145/extend-data-class-in-kotlin

[atsushi-koshikizawa]

Thanks you for answering!
I fixed my code like below.

interface FooBar {
    val foo: String
    val bar: String
}

interface Buz {
    val buz: String
}

data class Hoge(override val foo: String, override val bar: String) : FooBar

data class Fuga(override val foo: String, override val bar: String, override val buz: String) : FooBar, Buz