[Question]In what situations will af::copy() fail

TEST_CASE("af::copy()") {
double data[] = {1.0, 2.0, 3.0, 4.0, 5, 6, 7, 8,9,10,11,12,13,14,15,16,17,18};
af::array a(2, 3, 3, data);
af::array b(2, 3, 3, af::dtype::f64);

af::array at = a(af::seq(0, 1), af::seq(0, 1), af::seq(0, 1));
af::array bt = b(af::seq(0, 1), af::seq(0, 1), af::seq(0, 1));

af::copy(bt, at, af::span);

CHECK(b(0, 0, 0).scalar() == 0.0);
CHECK(b(1, 0, 0).scalar() == 0.0);
CHECK(b(0, 1, 0).scalar() == 0.0);
CHECK(b(1, 1, 0).scalar() == 0.0);

af::array at1 = a(af::seq(0, 1), af::seq(0, 0), af::seq(0, 0));
af::array bt1 = b(af::seq(0, 1), af::seq(0, 0), af::seq(0, 0));

af::copy(bt1, at1, af::span);

CHECK(b(0, 0, 0).scalar() == 1.0);
CHECK(b(1, 0, 0).scalar() == 2.0);
CHECK(b(0, 1, 0).scalar() == 0.0);
CHECK(b(1, 1, 0).scalar() == 0.0);
}