sealed class

when

private val handleDealOperation: (DealOperation) -> State.Change = {
            operation ->
            when (operation) {
                //how to enforce type safety? `DealOperation` is a sealed class
            }
        }

source.map(handleDealOperation)

operator fun <T> T.plus(collection: Collection<T>): List<T> {
    val result = ArrayList<T>(collection.size + 1)
    result.add(this)
    result.addAll(collection)
    return result
}

operator fun <T> FieldDelegate.getValue(thisRef: Any?, property: KProperty<*>): T {
    @Suppress("UNCHECKED_CAST")
    return when(property.returnType) {
        String::class -> ""
        Int::class -> 42
        else -> null
    } as T
}

notNull()

lateinit

s?.exit?.let { it() }

hashCode()

data class

data class Option(val id: Int, val desc: () -> String)

case

case

case