Call overridden method with default arguments

Question

In my Kotlin project I have following situation:

abstract class BaseConverter<T> {
    abstract fun serializeValue(output: ByteArray, value: T, offset: Int = 0): Int
}

object BooleanConverter: BaseConverter<Boolean>() {
    override fun serializeValue(output: ByteArray, value: Boolean, offset: Int): Int {
        output[0 + offset] = if(value) 1.toByte() else 0.toByte()
        return 1
    }
}

Now from my test cases I try to call BooleanConverter.serializeValue(array, value) which does not give me an IDE error message. However when I try to run the test I get following error:

Caused by: org.jetbrains.kotlin.codegen.CompilationException: Back-end (JVM) Internal error: wrong code generated [...] AnalyzerException: Argument 3: expected R, but found I

When I change my call to BooleanConverter.serializeValue(array, value, 0) everything works fine. But this makes my default value unnecessary. I also can not add the default value when overrideing the method because of:

an overriding function is not allowed to specify default values for its parameters

So why can't I call the method only with two arguments and is there any way to solve this?

Answer 1

You can use default parameters only with variables of parent class type (in which method with default parameters is declared). Try as a workaround:

val c: BaseConverter<Boolean> = BooleanConverter
c.serializeValue(array, value)

or without creating an extra variable:

(BooleanConverter as BaseConverter<Boolean>).serializeValue(array, value)