tryParse method
Implementation
int? tryParse(String formattedDateTime, int start, int end) {
var result = 0;
for (var i = start; i < end; i++) {
var digit = formattedDateTime.codeUnitAt(i) ^ 0x30;
if (digit <= 9) {
result = result * 10 + digit;
} else {
return null;
}
}
return result;
}