add method

@override Gregorian add({ int years = 0, int months = 0, int days = 0, })

makes a new date instance and add days, months and years separately

Original date object remains unchanged

Note: It does not make any conversion, it simply adds to each field value and changes ALL at once

This Method is NOT safe for month and day bounds

Recommended: Use separate add*() methods

Implementation

@override
Gregorian add({int years = 0, int months = 0, int days = 0}) {
  if (years == 0 && months == 0 && days == 0) {
    return this;
  } else {
    return Gregorian(
      year + years,
      month + months,
      day + days,
    );
  }
}