Lambda use cases. Simple example.

Dude.kt

public class Dude {
 
  // Easy way ¬¬ april, 14 2018
  
  fun main(args: Array<String>) {
    lambdaCall({
      System.out.println(it)
    })
  }
  
  fun lambdaCall(callback: (String) -> Unit) {
    // do work and then:
    callback("Hello")
  }
}

LambdaStudy_2.kt

/**
 * Created by overhead on 17/04/17.
 */

val numbers = arrayListOf<Int>(1, 2, 3, 4, 5, 6)

fun main(args: Array<String>) {
    // lambda 1
    containsEven(numbers)

    // lambda 2 using :: to signify a function reference
    println("1-1 = ${applyOperation(1, 1, ::subtract)}")
    println("1+1 = ${applyOperation(1, 1, ::add)}")
}

fun containsEven(collection: List<Int>): Unit = println("Even numbers are: ${collection.filter { it % 2 == 0 }}")

fun applyOperation(a: Int, b: Int, operation: (a: Int, b: Int) -> Int): Int {
    return operation(a, b)
}

fun add(a: Int, b: Int): Int {
    return a + b
}

fun subtract(a: Int, b: Int): Int {
    return a-b
}

/*
Reference:
https://goo.gl/xqGhJY
https://goo.gl/Jge4Gg
https://goo.gl/354D1g
 */