How to uninitialize lateinit in Kotlin

Question

I have a lateinit var as

lateinit var someVariable: SomeVariable

I initialize this value like someVariable = SomeVariable() and use it whenever I need.

At a certain point, I want to set everything to default and want to "uninitialize" someVariable. How can I do that?

I am not looking for changing its type to a nullable object and set null. I need to keep it a Non-Null type.

Answer 1

I don't think it's possible without some kind of wrapper (or reflection, but about it in a moment).

In fact, lateinit is design for compatibility with DI frameworks etc. If you know the value can be uninitialized in any moment then you should use nullable type.

So, what about that reflection thing? lateinit is in fact a kind of smart wrapper that makes nullable value to act like not nullable, and instead of throwing NullPointerException throws UninitializedPropertyAccessException. lateinit property at the moment of declaration in JVM is null, so, let's make it null again ;)

So...

class MyClass {
    lateinit var lateinitObject: Any

    fun test() {
        println("Is initialized: ${::lateinitObject.isInitialized}") // false
        lateinitObject = Unit
        println("Is initialized: ${::lateinitObject.isInitialized}") // true

        resetField(this, "lateinitObject")
        println("Is initialized: ${::lateinitObject.isInitialized}") // false

        lateinitObject // this will throw UninitializedPropertyAccessException
    }
}

fun resetField(target: Any, fieldName: String) {
    val field = target.javaClass.getDeclaredField(fieldName)

    with (field) {
        isAccessible = true
        set(target, null)
    }
}

fun main() {
    MyClass().test()
}

So, setting that field to null (and it's possible only via reflection) makes this filed uninitialized again. And one important thing - treat it as a curiosity, not like thing that should be in your production code.