Hi guys! I have something like this: ``` interface...

# announcements

[nicola.de.fiorenze]

Hi guys!
I have something like this:

interface Base {
    fun print()

    fun getValue() : String
}

class BaseImpl : Base {

    override fun print() { print(getValue()) }

    override fun getValue(): String {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }
}

class Derived(private val b: Base) : Base by b {
    override fun getValue(): String = "hello"
}

fun main(args: Array<String>) {
    val b = BaseImpl()
    Derived(b).print() // prints 10
}

obviously the output is

Exception in thread "main" kotlin.NotImplementedError: An operation is not implemented: not implemented
	at BaseImpl.getValue(Main.kt:12)
	at BaseImpl.print(Main.kt:9)
	at Derived.print(Main.kt)
	at Main3Kt.main(Main.kt:22)

which is the cleanest way to refactor this snippet to specify in Derived what should be used in BaseImpl.print()?

[Andreas Sinz]

@ndefiorenze There is no simple way to do that with delegation, because you are not really inheriting anything from BaseImpl, but rather redirect method calls to BaseImpl, so its still using its own print()

[Andreas Sinz]

easiest way would be to use inheritance instead of delegation, that way you can override getValue()

[Andreas Sinz]

with inheritance:

class BaseWithCustomGetValue(val base: Base, val customGetValue: () -> String) : Base by base {
    override fun getValue() = customGetValue()
}

class Derived(private val b: Base) : Base by BaseWithCustomGetValue(b, { "Hello" }) {
}