fun <T : Any> notNull(): ReadWriteProperty<Any?, T>

Returns a property delegate for a read/write property with a non-null value that is initialized not during object construction time but at a later time. Trying to read the property before the initial value has been assigned results in an exception.

import kotlin.properties.Delegates

import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
var max: Int by Delegates.notNull()

// println(max) // will fail with IllegalStateException

max = 10
println(max) // 10
//sampleEnd
}