functionReturningFunction.kt

 private fun simpleDemo() {
        retrieveUserFromNetwork("111") {
            println(it.userName)
        }
    }

    private fun retrieveUserFromNetwork(
        userId:String,
        userRetrieved:(user:User) -> Unit
    ) {
       thread {
           Thread.sleep(1000)
           val user = User(userId,"TestUser")
           userRetrieved(user)
       }
    }

    data class User(val userId:String,val userName:String)