import core.time;
import std.datetime.date : DateTime;
assert(SysTime(DateTime(1, 1, 1, 12, 7, 0)).isAD);
assert(SysTime(DateTime(2010, 12, 31, 0, 0, 0)).isAD);
assert(!SysTime(DateTime(0, 12, 31, 23, 59, 59)).isAD);
assert(!SysTime(DateTime(-2010, 1, 1, 2, 2, 2)).isAD);
Whether the current year is a date in A.D.