Hi I'm wondering if I have reached a limitation, bug or just a misunderstation of Kotlin. I'm trying...

# getting-started

[jeggy]

Hi I'm wondering if I have reached a limitation, bug or just a misunderstation of Kotlin.
I'm trying to overwrite a function that is being used by another function implemented by a delegated implementation, like shown below:

interface Run {
    fun printA()
    fun printWith(value: String)
}

val DefaultRun = object: Run {
    override fun printA() = printWith("value")
    override fun printWith(value: String) = println("Hello with: $value")
}

class Custom: Run by DefaultRun {
    override fun printWith(value: String) = println("Goodnight with: $value")
}

fun main() {
    // Prints "Hello with: value"
    // But I expected it to print "Goodnight with: value"
    Custom().printA() 
}

[David Kubecka]

See the "however" note in https://kotlinlang.org/docs/delegation.html#overriding-a-member-of-an-interface-implemented-by-delegation

[Youssef Shoaib [MOD]]

That's an interesting place where using an extension function changes behaviour a lot:

interface Run {
    fun printWith(value: String)
}

fun Run.printA() = printWith("value")

val DefaultRun = object: Run {
    override fun printWith(value: String) = println("Hello with: $value")
}

class Custom: Run by DefaultRun {
    override fun printWith(value: String) = println("Goodnight with: $value")
}

fun main() {
    // Prints "Goodnight with: value"
    Custom().printA() 
}

[jeggy]

good idea. Will just go with this route 👌