KotlinExtensionsActivity.kt

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_kotlin_extensions)
 
    welcomeMessage.text = "Hello Kotlin!"
    helloButton.setOnClickListener { toast.("Hello Kotlin") }
}

fun setMessaeg(message: String) {
   welcomeMessage.text = message // this wont call findViewById again 
}