     
     func isFirstLetterDigit() -> Bool {
         
-        guard let c : Character = self.characters.first else {
+        guard let c : Character = self.first else {
             return false
         }
         

    
    internal init(_ shortFlag: String?, _ longFlag: String?, _ required: Bool, _ helpMessage: String) {
        if let sf = shortFlag {
            assert(sf.characters.count == 1, "Short flag must be a single character")
            assert(Int(sf) == nil && Double(sf) == nil, "Short flag cannot be a numeric value")
        }
        

        
        let doubleCharacteristic = Double(Int(characteristic)!)
        return (doubleCharacteristic +
            Double(Int(mantissa)!) / pow(Double(10), Double(mantissa.count - 1))) *
            (isNegative ? -1 : 1)
    }
    
