extension Array {
    subscript(safeAt index: Int) -> Element? {
        //Out of boundaries
        if count <= index || index < 0 { return nil }
        return self[index]
    }
}

let ints = [1,2,3,4]
ints[safeAt: 3]
ints[safeAt: -1]
ints[safeAt: 0]
ints[safeAt: 5]