get word at a given position in a string.swift

func wordRangeAtIndex(index:Int, inString str:NSString) -> NSRange {
    let tagger = NSLinguisticTagger(tagSchemes: [NSLinguisticTagSchemeTokenType], options: 0)
    var r : NSRange = NSMakeRange(0,0)
    tagger.string = str as String
    tagger.tagAtIndex(index, scheme: NSLinguisticTagSchemeTokenType, tokenRange: &r, sentenceRange: nil )
    return r
}

func wordAtIndex(index:Int, inString str:NSString) -> NSString {
    return str.substringWithRange(wordRangeAtIndex(index, inString: str))
}