Array Indexing

[jramapuram]

Is it possible at this point to indexing arrays by implementing IndexMut, etc? It would be nice to do be able to do the following a[x_index][y_index][z_index][d_index]

Ideally it would be great to be able to have ranges inside as well [numpy style], eg:
a[0..x_index][y_index][z_index][d_index]

and even negative indexing to pick elements from the end:
a[-1][y_index][z_index][d_index]

Relevant SO post. I believe dynamic types are already in now?

[9prady9]

Being able to do such terse indexing would be a good addition. Yes, i have heard that dynamic types are in, but i am not aware of all of the details. Will have to look into them.

[9prady9]

@jramapuram I was thinking about how to implement this using the c++ version of ArrayFire as baseline. What i have noticed is that c++ API in ArrayFire heavily uses assignment operator overload and we have no control of assignment operator in Rust, please correct me if i am wrong in this observation. So, i am wondering how crucial is this for implementing indexing in above fashion.

[jramapuram]

@9prady9 : Isn't assignment simply Copy or Clone in rust? We have an impl of Clone. However, not sure if I understand how this is related. Wouldn't it just be implementing the IndexMut operations? Inside that it would be calls to af::index or one of the other indexing functions in index.rs

[9prady9]

True, i forgot about clone trait (copy is not available if drop is implemented - unless this changed recently).

ArrayFire's C++ wrapper uses proxy pattern for indexing efficiently. You can have a peek at the following sections of code to understand how it is being done in that wrapper.

• proxy class declaration
• proxy class implementation
• proxy class assignment operator overload

I believe we might have to do something similar in Rust too after we get the index ranges from Index and IndexMut traits. Hence, i was thinking about the assignment operation, clone trait didn't cross my mind at that point.

[jramapuram]

How about a slicing macro like this? http://bluss.github.io/rust-ndarray/master/ndarray/macro.s.html

[Timmmm]

Maybe I'm missing something, but is there any way to set a single element at the moment? I couldn't find a set_element() function or anything like that...

[9prady9]

@Timmmm You should be using either assign_gen or assign_seq depending on your use case.

But ideally, such writes are only good in performance if you are writing considerable number of elements. Writing single elements is very inefficient in terms of data transfers done from host to GPU/accelerator device.

[9prady9]

@jramapuram Are macros allowed on left hand side of equal operator in rust ?