Kotlin_Composition.kt

interface Fooable {
  fun foo(): String
}

class FooImpl : Fooable {
  override fun foo() = "I am fooImpl"
}

class AnotherFooImpl : Fooable {
  override fun foo() = "I am anotherFooImpl"
}

class X(impl: Fooable) : Fooable by impl

fun main(args: Array<String>) {
  val x = X(FooImpl())
  println(x.foo()) //print I am fooImpl
  
  val y = X(AnotherFooImpl())
  println(y.foo()) //print I am anotherFooImpl
}