Functional Kotlin

The power of veto – Delegates.vetoable

Delegates.vetoable is another standard delegate that allows us to veto a value change.

A veto, Latin for I forbid, is the power (for example, used by an officer of the state) to unilaterally stop an official action. There is more information here: https://en.wikipedia.org/wiki/Veto.

This right to veto allows us to have a logic check on each assignment of the property, where we can decide to continue with the assignment or not.

The following is an example:

var myIntEven:Int by Delegates.vetoable(0) { 
    property, oldValue, newValue -> 
    println("${property.name} $oldValue -> $newValue") 
    newValue%2==0 
} 
 
fun main(args: Array<String>) { 
    myIntEven = 6 
    myIntEven = 3 
    println("myIntEven:$myIntEven") 
} 

In this program, ...