KotlinHigherOrderMessagePassing

Kotlin Higher Order Message Passing with a Lamba

http://ios.robertlinnemann.com/kotlin-higher-order-function-lambda/

This example is basically showing how to pass a function as a parameter to an object that can then be called from within. I use a String but it could be any parameters or none. Comparing to an interface it is a bit cleaner and a bit less code. Interfaces are great when you need multiple functions but using a Lambda works great for just a function and is just as clear.

/**
** Higher-Order Function as parameter to a class.
** Robert Linnemann
**/

fun main(args: Array<String>) {
    //make an object that makes an internal object.
    val m = Master()
    //call a function on the internal object that then calls
    //through to the lamda function that was passed into it.
    m.apprentice?.sendMessage()
}

class Master {
      var apprentice: Apprentice?
    init {
        //pass in the function print to the Apprentice object.
	       apprentice = Apprentice(::print)        
    }

    fun print(message: String) {
        println(message)
    }
}

class Apprentice(send: (String) -> Unit) {
    val send = send
    fun sendMessage() {
        send("Print This for me.")
    }
}

I’ve also implemented an interface alongside which compares these features a bit better.

fun main(args: Array<String>) {
    //make an object that makes an internal object.
    val m = Master()
    //call a function on the internal object that then calls
    //through to the lamda function that was passed into it.
    m.apprentice?.sendMessageThroughLambda()
    //A similar was to pass a message to a parent object would be to
    //use an interface
    m.apprentice?.sendMessageThroughInterface()
}

interface PassMessageListener {
    fun message(message: String)
}

class Master: PassMessageListener {
      var apprentice: Apprentice?
    init {
        //pass in the function print to the Apprentice object.
	       apprentice = Apprentice(::print)    
        //setup the interface listener
        apprentice?.passMessageListener = this
    }

    fun print(message: String) {
        println(message)
    }
    //interface method
    override fun message(message: String) {
        print(message)
    }
}

//This gets a function passed in as the variable 'send'.
class Apprentice(send: (String) -> Unit) {
    val send = send
    var passMessageListener: PassMessageListener? = null
    
    fun sendMessageThroughLambda() { 
        //sends directly to the function on a whole 'notha level
        send("Print this for me.")
    }
    fun sendMessageThroughInterface() {
        //traditional interface way to pass a message
        passMessageListener?.message("Print this for you")
    }
}

To run this you can put it into the great site https://try.kotlinlang.org/ or compile it from the command line (install tools). I prefer using sdkman.io Then run these commands:

kotlinc higherOrder.kt -include-runtime -d higherOrder.jar java -jar higherOrder.jar

mevdev/KotlinHigherOrderMessagePassing

KotlinHigherOrderMessagePassing