How can I delegate an implementation to a mutable property in Kotlin?

Question

As to my understanding, the idea of delegating an implementation in Kotlin is to avoid code that looks like this:

Answer 1

Sadly, as far as I know there is no way of changing the delegate by changing the original property content, but you might still be able to do something similar by working in an immutable way and copying the object:

interface MyInterface {
  fun foo():Int
}

data class MyClass(val delegate : MyInterface) : MyInterface by delegate

object ImplementationA: MyInterface { override fun foo() = 7 }
object ImplementationB: MyInterface { override fun foo() = 5 }

val objA = MyClass(ImplementationA)
println(objA.foo()) // returns 7

val objB = objA.copy(ImplementationB)
println(objB.foo()) // returns 5
println(objA.foo()) // still 7

Hope this is still useful.