set_fancy does not work for some arrays with certain Bigarray.kind types.

[zoj613]

When using Owl.Dense.Ndarray.Generic.set_fancy with arrays of kinds not Float32, Float64, Complex32 or Complex64, the operation fails with error message Exception: Failure "_ndarray_set_fancy: unsupported operation", even though the kind is a valid Bigarray.kind type.

It appears this exception is thrown by the snippet:

owl/src/owl/core/owl_slicing_fancy.ml

Lines 92 to 105 in 600c21a

	let _ndarray_set_fancy
	: type a b c.
	(a, b) kind
	-> (a, b) owl_arr
	-> (a, b) owl_arr
	-> (int64, c) owl_arr
	-> (int64, c) owl_arr
	-> unit
	= function
	| Float32 -> owl_float32_ndarray_set_fancy
	| Float64 -> owl_float64_ndarray_set_fancy
	| Complex32 -> owl_complex32_ndarray_set_fancy
	| Complex64 -> owl_complex64_ndarray_set_fancy
	| _ -> failwith "_ndarray_set_fancy: unsupported operation"

I think it is very limiting to only support just 4 kinds when the set operation should work for any of the Bigarray.kind types.

Here is a minimal example to reproduce the error:

module Ndarray = Owl.Dense.Ndarray.Generic
let arr = Ndarray.create Bigarray.Int32 [|3;4;3|] 5l
let slice = Owl_types.[L [1; 2]; R []; I 0]
let x = Ndarray.create Bigarray.Int32 [|2; 4; 1|] 0l
 Ndarray.set_fancy slice arr x

I expected this simple operation to work but it throws a |Exception: Failure "_ndarray_set_fancy: unsupported operation". exception.

I would love for Owl to support more kinds as im using it to write an array library that needs to support more than the 4 basic kinds listed above.

Cc @mseri @jzstark

[zoj613]

I was able to implement a temporary workaround to this issue by using element-wise set. Basically:

1. Convert the slice to a list of coordinates of the target array.
2. Use Owl.Dense.Ndarray.Generic.set and List.iter2 to iterate over the list of coordinates and values and set them one at a time

 List.iter2
  (fun coord val ->
	Owl.Dense.Ndarray.Generic.set coord val) coord_list value_list

I would like to add that this issue also affects the transpose function as well. The offending lines are:

owl/src/owl/core/owl_ndarray_transpose.ml

Lines 41 to 54 in 455bde1

	let _ndarray_transpose
	: type a b.
	(a, b) kind
	-> (a, b) owl_arr
	-> (a, b) owl_arr
	-> (int64, int64_elt) owl_arr
	-> (int64, int64_elt) owl_arr
	-> unit
	= function
	| Float32 -> owl_float32_ndarray_transpose
	| Float64 -> owl_float64_ndarray_transpose
	| Complex32 -> owl_complex32_ndarray_transpose
	| Complex64 -> owl_complex64_ndarray_transpose
	| _ -> failwith "_ndarray_transpose: unsupported operation"

Unfortunately, I haven't been able to find a workaround for this