How to nest multiple property delegates in Kotlin - kotlin

Question

I've come accross a case where I want to "chain" mutliple delegates (piping the output of one into the other).
This seems to be possible:
private val errorLogList by listSO(listOf<StateObject<Luxeption>>(), SODest.NONE, publicSOAccessRights())
val errorLog: StateObject<List<StateObject<Luxeption>>> by addToSet(errorLogList)
However, this does not look too well :). I'd like to do it in one line like this:
val errorLog: StateObject<List<StateObject<Luxeption>>> by addToSet(
listSO(listOf<StateObject<Luxeption>>(), SODest.NONE, publicSOAccessRights())
)
My question: Is this type of creating properties through delegates possible in Kotlin?
Here are both implementations of my delegates:
addToSet:
open class ChildSOReturner {
val set: Set<StateObject<*>> = setOf()
inline fun <reified T> addToSet(so: T) = object: ReadOnlyProperty<Any?, T> {
override operator fun getValue(thisRef: Any?, property: KProperty<*>): T {
if (thisRef is T) {
set.plus(so)
return so
} else throw IllegalArgumentException()
}
}
}
listSo:
fun <O> listSO(
initialState: List<StateObject<O>>,
soDest: SODest,
soAccessRights: SOAccessRights
) = object : ReadOnlyProperty<Any?, StateObject<List<StateObject<O>>>> {
override operator fun getValue(thisRef: Any?, property: KProperty<*>): StateObject<List<StateObject<O>>> {
val meta = SOMeta(SOId(property.name), soDest, soAccessRights)
return StateObjectList(initialState, meta)
}
}

Answer 1

It turned out to be quite tricky, but possible (unless I am missing something, and it isn't tested but the idea should work):
fun <T, U, V> composeProperties(prop: ReadOnlyProperty<T, U>, f: (U) -> ReadOnlyProperty<T, V>) : ReadOnlyProperty<T, V> {
var props = mutableMapOf<Pair<T, KProperty<*>>, ReadOnlyProperty<T, V>>()
return object : ReadOnlyProperty<T, V> {
override operator fun getValue(thisRef: T, property: KProperty<*>): V {
val prop1 = props.getOrPut(Pair(thisRef, property)) {
f(prop.getValue(thisRef, property))
}
return prop1.getValue(thisRef, property)
}
}
}
And then to use
val errorLog: ... by composeProperties(listSO(...)) { addToSet(it) }