Kotlin Programming Cookbook

How to do it…

Let's now look at the given steps to understand the vetoable modifier:

1. Let's take a quick look at an implementation of the vetoable delegated property:

fun main(args: Array<String>) {    var student:Student by Delegates.vetoable(Student(10),{property, oldValue, newValue ->        if(newValue.age>25){            println("Age can't be greater than 25")            return@vetoable false        }        true    })    student=Student(26)}class Student(var age:Int)

//Output: Age can't be greater than 25

2. As you can see, the modification is "vetoed" by the vetoable delegate since the age can't be greater than 25. The new object will only be assigned if the age is less than 25.