I think the user can use an external keyboard via Bluetooth, so it is better to provide for the input of both a dot and a comma:   func replaceComma(str: String) - Double {         if let range = str.range(of: ",") {             let testStr = str.replacingCharacters(in: range, with: ".")             return Double(testStr) ?? 0         } else {             return Double(str) ?? 0         }     }