Will prepend 1s until dimension sizes match, then 1s are treated as wildcards and are broadcasted to their matching sizes.

array A = range(dim4(32, 32, 3), 2);  // [32 32 3]
array B = -range(dim4(3)); //    [ 3 ] -> [1* 1* 3]

array C = A + B; // [32 32 3]

In cases where one of the arguments is a vector, prepending until dimensions match may not align well:

 array A = constant(-1, dim4(15, 3, 5)); // [15 3 5]
 array B = constant(1, dim4(3, 1));        // [ 1  1 3] - misaligned,
 // even though 3 intended to broadcast with second dimension of A

Upon a mismatch, the prepended vectors will be shifted left until there is a match. In the above example the broadcast will be a success after a single additional shift.

This manner of treating vectors is a workaround due to no difference between.

af::dim4 d1(3);
af::dim4 d2(3, 1);
af::dim4 d3(3, 1, 1);
af::dim4 d4(3, 1, 1, 1);
// d1 == d2 == d3 == d4

TODO:

• n-ary operations?
• complex values