indexOf is throwing "Object type does not match RLMResults" exception

[ahayman]

I've written a persistence layer around RealmSwift. Everything works fine except I can't seem to use indexOf. When I do, it throws: Object type does not match RLMResults. However, even when I look in the debugger, it shows I'm passing in the correct object type to indexOf. Further details:

In order to "wrap" Realm, I had to create a translation layer to translate between the Realm objects and the "Model" objects I use in the rest of the app.

Example:

public protocol Translator {
  func translate(from: Object) -> Model
  func translate(from: Model) -> Object
}

I created a wrapper around Results, I called Dataset. The Dataset uses a Translator to translate between the objects returned by Results and the Model objects the rest of the app uses.

Because of the limitations of Swift, I could not directly wrap Results<T> (Swift generic types are invariant). So instead, I extended Results with a protocol to provide the functions I needed.

protocol RealmResults {
  func objectAt<T: Object>(index: Int) -> T
  var objectCount: Int { get }
  func indexOfObject<T: Object>(object: T) -> Int?
  func filterOn(predicate: NSPredicate) -> RealmResults
  func sortOn(sorts: [SortDescriptor]) -> RealmResults
}

extension Results : RealmResults {
  func objectAt<T : Object>(index: Int) -> T {
    return self[index] as! T
  }

  var objectCount: Int {
    return count
  }

  func indexOfObject<U : Object>(object: U) -> Int? {
    if let realmObject = object as? T {
      return indexOf(realmObject)
    }
    return nil
  }

  func filterOn(predicate: NSPredicate) -> RealmResults {
    return filter(predicate)
  }

  func sortOn(sorts: [SortDescriptor]) -> RealmResults {
    return sorted(sorts)
  }
}

So Dataset wraps RealmResults and accesses Results<T> using the protocol. This all works fine, except for indexOfObject. It throws Object type does not match RLMResults even though I'm passing in the exact object that Results is expecting.

You can see from the debugger that Results is: Results<MessageObject> and the type I'm passing in is MessageObject. Any idea why this may be happening? Is it an issue or am I missing something?

[segiddins]

Just a guess, but is the object you're passing in not persisted? If that's indeed the issue, I'm preparing a patch right now both to (a) allow that and (b) give a more informative error when the classes actually don't match.

[ahayman]

Yes, actually, the object I'm passing in is not persisted, and I'm trying to match it against an object that may be persisted. Is that the issue? The "translator" simply takes a Model object and creates a new "Realm" object from it. Chances are, it's going to exactly match what is persisted, but the actual object itself isn't persisted. It's only created for comparison purposes.

[segiddins]

@ahayman ok, cool! This will be fixed by #2356, since checking for the index of an unpersisted object should just return nil.

[ahayman]

Great! Thanks! In the meantime, I can easily work around it by using indexOf(NSPredicate)