How to return values from Haneke's async fetch method - swift

Question

I'm trying to parse some data that I cached using Haneke Swift. I've cached the data and have written the parser to accomplish this. This parser is in a separate class called AssembleCalendar().
Using Haneke's example code for fetching, I've tried with complete and utter failure to actually return a value from the closure.
My attempt
func getScheduledItems() -> [ScheduledItem] {
var scheduledItem = [ScheduledItem]() // initialize array
let cache = Shared.dataCache
cache.fetch(key: "CalendarData").onSuccess { data in
scheduledItem = AssembleCalendar().assimilate(data) // update array
print(scheduledItem) // array returns expected value
}
print(scheduledItem) // array returns nil
return scheduledItem // returns nil
}
What I know
I understand that this is an asynchronous issue. My code isn't waiting for my AssembleCalendar() parser to finish. It's just running each line and returns nil long before my scheduledItem receives a value. I've tried many, many solutions and read quite a few examples online but I cannot figure out how to retrieve a value from this closure in this scenario.
My question
How can I get .fetch() to return a value before my function hits nil?
update:
Here's my code in context:
class Schedule {
var items : [ScheduledItem]
init() {
items = getScheduledItems() // Schedule.getScheduledItems()
}
func getScheduledItems(completion: (items: [ScheduledItem]) -> ()) {
var scheduledItem = [ScheduledItem]() // initialize array
let cache = Shared.dataCache
cache.fetch(key: "CalendarData").onSuccess { data in
scheduledItem = AssembleCalendar().assimilate(data) // update array
print(scheduledItem) // array returns expected value
completion(items: scheduledItem)
}
}
}

Answer 1

Fetch() is using a completion handler, this means that the block of code called in there is actually executing AFTER your return statement has been executed. This is why it is returning nil. To get around this, you can use your own completion handler to return the information:
class Schedule {
var items = [ScheduledItem]()
init(items: [ScheduledItem]) {
self.items = items
}
class func getScheduledItems(completion: (items: [ScheduledItem]) -> ()) {
var scheduledItem = [ScheduledItem]() // initialize array
let cache = Shared.dataCache
cache.fetch(key: "CalendarData").onSuccess { data in
scheduledItem = AssembleCalendar().assimilate(data) // update array
print(scheduledItem) // array returns expected value
completion(items: scheduledItem)
}
}
}
Then initialise the class using this:
Schedule.getScheduledItems { (items) -> () in
var schedule = Schedule(items: items)
}