isValid method Null safety
- String cardNumber
Implementation
bool isValid(String cardNumber) {
return cardNumber.substring(cardNumber.length - 1) ==
_calculate(cardNumber.substring(0, cardNumber.length - 1));
}
bool isValid(String cardNumber) {
return cardNumber.substring(cardNumber.length - 1) ==
_calculate(cardNumber.substring(0, cardNumber.length - 1));
}