An attempt to create an example to narrow down my question on Stackoverflow

awaitility-so-54249929.kts

// Fake Awaitility DSL
data class AwaitilityKtUntilFunCondition<T>(val factory: ConditionFactory, val fn: () -> T) {
    infix fun has(pred: T.() -> Boolean) = factory.until(fn) { t: T? ->
        if (t == null) {
            false
        } else {
            pred(t)
        }
    }
}

class ConditionFactory {
    fun <T : Any?> until(supplier: () -> T, predicate: (T) -> Boolean): T {
        val result = supplier()
        return if (predicate(result)) {
            result
        } else {
            throw IllegalArgumentException("Supplied value is not matching predicate")
        }
    }
}

class Await {
    infix fun <T> untilCallTo(supplier: () -> T): AwaitilityKtUntilFunCondition<T> {
        val conditionFactory = ConditionFactory()
        return AwaitilityKtUntilFunCondition(conditionFactory, supplier)
    }
}

// Example

data class Data(var state: String)
interface DataRepository<T> {
    fun loadData(): T
}

val nullableDataRepository: DataRepository<Data?> = TODO()
val nonNullableDataRepository: DataRepository<Data> = TODO()


// Test - A want both of these to compile!


val data1: Data = Await() untilCallTo { nonNullableDataRepository.loadData() } has {
    state == "something"
}

val data2: Data = Await() untilCallTo { nullableDataRepository.loadData() } has {
    state == "something"
}