struct LargeArray: Sequence {
    var contents: (Int * 10000)

    func makeIterator() -> Iter {
        return Iter(array: self, index: 0)
    }
}

struct Iter: IteratorProtocol {
    var array: LargeArray
    var index = 0

    mutating func next() -> Int? {
        defer { index += 1 }
        return array[index]
    }
}