extension String {

  subscript (i: Int) -> Character {
    return self[self.startIndex.advancedBy(i)]
  }

  subscript (i: Int) -> String {
    return String(self[i] as Character)
  }

  subscript (r: Range<Int>) -> String {
    return substringWithRange(Range(start: startIndex.advancedBy(r.startIndex), end: startIndex.advancedBy(r.endIndex)))
  }
}