extension String {
subscript (i: Int) -> Character {
return self[self.characters.index(self.startIndex, offsetBy: i)]
}
subscript (i: Int) -> String {
return String(self[i] as Character)
}
subscript (r: Range<Int>) -> String {
let start = characters.index(startIndex, offsetBy: r.lowerBound)
let end = characters.index(start, offsetBy: r.upperBound - r.lowerBound)
return String(self[Range(start ..< end)])
}
}