// SomeClass.kt

interface SomeInterface {
    fun someMethod()
}

private class SomeClassProxy(
    private var someClass: SomeClass?
): SomeInterface {
    override fun someMethod() { someClass?.someMethod() }
}

class SomeClass private constructor(): SomeInterface {
	fun someMethod() { println("Hello"); }
	
	companion object {
		fun useNew(func: SomeInterface.() -> Unit) {
            val someClass = SomeClass()
            val proxy = SomeClassProxy(someClass)
			proxy.func()
            proxy.someClass = null
		}
	}
}
​
// Main.kt
fun main() {
	var sc: SomeClass? = null
	SomeClass.useNew {
		this.someMethod()
		sc = this // I want this not to be possible
	}
	sc?.someMethod() // or at least this
}