Kotlin Programming Cookbook

How to do it…

Now, let's dive in and learn how to create our own delegates:

1. Let's create a custom delegate named as  SingleInitializationProperty. This custom delegate property will throw an exception if the variable isn't initialized, and it can only be initialized once. Doing it a second time will throw an exception. Let's take a look at our custom delegate class:

class SingleInitializableProperty<T>() : ReadWriteProperty<Any?, T>{    private var value: T? = null    override fun getValue(thisRef: Any?, property: KProperty<*>): T {        if(value==null){            throw IllegalStateException("Variable not initialized")        }else {            return value!!        }    }    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {        if(this.value==null){            this.value=value