Dataclass exhibits dangerous behavior returning original values on destructuring

data class MyDataClass(
    var a: String,
    var b: Number? = null,
    val c: Boolean,
    private var d: Double

val myDataClass = MyDataClass(a = "hello", c = true, d = 1.20)

myDataClass.b = 1
myDataClass.a = "goodbye"

val (a,b,c) = myDataClass
println(listOf(a, b, c)) // [hello, null, true]
println(listOf(myDataClass.a, myDataClass.b, myDataClass.c)) // [goodbye, 1, true]

I would have expected destructuring my dataclass class instance to return [goodbye, 1, true] as well but not only is it not returning updated values for it’s properties, it’s actually exhibiting two silent behaviors: it’s returning the passed in value for parameter a (“hello”), it’s returning the default value for parameter b (null). Basically two different behavior, and neither of these behaviors are documented on the Kotlin docs either under destructuring.

Most likely I’ve made a mistake, but if not, I would consider this to be non-intuitive behavior and likely to lead to bugs.

here’s my env:

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Actually I tried this is the kotlin online playground and it returns the destructured values as expected, so it seems to not be a language issue (relief :smiley:). It seems this is a problem with Idea scratch playground? See

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Created issue on jetbrains