none

auto vopt = none!int;
assert(vopt.isNone);
vopt = 12;
assert(vopt.isSome);
assert(vopt.front == 12);

// auto ropt = none!CTest;
// assert(ropt.isNone);
// assert(ropt._val is null);
// ropt = new CTest;
// assert(vopt.isSome);