toDateString method
This date as a simple "year-month-day" string.
If the year is negative, it starts with a minus sign. The year is padded to at least four digits, the month and day to two digits.
Implementation
String toDateString() {
final year = this.year;
final month = this.month;
final day = this.day;
String yearString;
if (year.abs() < 1000) {
yearString = year.abs().toString().padLeft(4, '0');
if (year < 0) yearString = '-$yearString';
} else {
yearString = year.toString();
}
return "$yearString-${month < 10 ? "0" : ""}$month-${day < 10 ? "0" : ""}$day";
}