Constructs a YearMonthDay from a year, month, and day, or from a Date object.
auto d = YearMonthDay(2020, Month.may, 31); auto ym = d.YearMonth; assert(ym.year == 2020); assert(ym.month == Month.may);
Constructs a YearMonthDay from a year, month, and day, or from a Date object.