+= produces '()', not the expected contextual result type UInt

Question

I am migrating swift 2.2 to swift 3.0 as ++ operator removed in swift 3. but i am getting following error while converting i++ to i+=1

error:+= produces '()', not the expected contextual result type UInt

Here is my code:

public func makeIterator() -> AnyIterator<RLMObject> {
    var i: UInt  = 0
    return AnyIterator {
        if (i >= self.count) {
            return .none
        } else {

            return self[i += 1] as? RLMObject
        }
    }
}