Why doesn't Kotlin allow to use lateinit with primitive types?

Question

In the Kotlin language we, by default, have to initialize each variable when it is introduced. To avoid this, the lateinit keyword can be used. Referring to a <

Answer 1

A short answer is that with primitives you can always use 0 as the default, and with nullable types null as a default. Only non-nullable non-primitive types may need lateinit to work around the type safety system.

Actually, there is no need for initializing a variable in Kotlin as long as it has a value before the first access and it can be statically proved. Which means this code is perfectly valid:

fun main(args: Array) {
    var x: Int
    val y: Double

    x = 0
    y = x + 0.1

    println("$x, $y") 
}

But there are (rare) cases when the initialisation cannot be statically proved. The most common case is a class field which uses any form of dependency injection:

class Window {
    @Inject lateinit parent: Parent
}