Way to update sorted/unsorted NSManagedObject relationship

NSManagedObject+Relationship.swift

extension NSManagedObject {

    func updateToManyRelationship<T: NSManagedObject & Managed, J: SetInitable & SetGettable>(relationship: String, newValues new: [T]?, setClass: J) {
        // Store our old values so we can reference them later
        let oldSet = value(forKeyPath: relationship) as? J
        let oldValues = oldSet?.items as? [T]

        // The ol' switcharoo
        let newSet = Set(new ?? [])
        setValue(J(set: newSet), forKey: relationship)

        // Clean up orphans, if applicable
        if let oldValues = oldValues {
            let oldSet = Set(oldValues)
            oldSet.subtracting(newSet).filter({ $0.isOrphaned }).forEach({
                managedObjectContext?.delete($0)
            })
        }
    }

}

protocol SetInitable {
    init(set: Set<AnyHashable>)
}

protocol SetGettable {
    var items: [Any] { get }
}

extension NSSet: SetGettable {
    var items: [Any] {
        return allObjects
    }
}

extension NSOrderedSet: SetGettable {
    var items: [Any] {
        return array
    }
}