{
auto arr = [1, 2, 3];
auto r = arr.whenEmpty((){ arr = null; });
assert(equal(r, arr));
assert(arr is null);
}
{
auto arr = [1, 2, 3];
auto r = arr.whenEmpty((){ arr = null; });
//assert(equal(r, arr));
r.popFront(); r.popFront();
assert(arr !is null);
r.popFront();
assert(arr is null);
}