A string when not using an output range; void otherwise.
assert(Date.init.toISOString == "null"); assert(Date(2010, 7, 4).toISOString == "20100704"); assert(Date(1998, 12, 25).toISOString == "19981225"); assert(Date(0, 1, 5).toISOString == "00000105"); assert(Date(-4, 1, 5).toISOString == "-00040105", Date(-4, 1, 5).toISOString());
Converts this Date to a string with the format YYYYMMDD. If writer is set, the resulting string will be written directly to it.