Implement to_mdspan

[jefffaust]

This proposal describes to_mdspan.

I would find this quite useful, especially if it would work when dequeu is the underlying mdarray container.

[mhoemmen]

@jefffaust Thanks for your interest! The mdarray class template requires that the container be contiguous. deque is not a contiguous container.

The main benefit of deque is that insertion or deletion at its beginning or end does not invalidate pointers or references to the other elements. However, mdarray cannot be resized after creation, so this benefit does not apply.

One could write a custom mdspan accessor to view the elements of a deque.

[jefffaust]

I was afraid of that. The other benefit of deque, and the reason I'd like to use it, is that it can hold much larger sets of data. My workaround is a vector of 2d mdarray, instead of a 3d mdarray, which makes a lot of sense for my case. Also wanted to let you know, we're getting a lot of benefit from mdspan and mdarray. Thanks, Jeff

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On Wed, Mar 8, 2023, 8:12 AM Mark Hoemmen ***@***.***> wrote: @jefffaust <https://github.com/jefffaust> Thanks for your interest! The mdarray class template requires that the container be contiguous. deque is not a contiguous container. The main benefit of deque is that insertion or deletion at its beginning or end does not invalidate pointers or references to the other elements. However, mdarray cannot be resized after creation, so this benefit does not apply. One could write a custom mdspan accessor to view the elements of a deque. — Reply to this email directly, view it on GitHub <#244 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFMO4FCQHM2UULGNKCJD5BTW3CVVZANCNFSM6AAAAAAVTCK6K4> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[mhoemmen]

@jefffaust wrote:

...we're getting a lot of benefit from mdspan and mdarray.

We're delighted to hear that! Thank you for the feedback! : - )

Regarding mdarray requiring a contiguous container: the general principle is that views are more general than containers. span can represent any 1-D contiguous array view, while vector represents a more specific use case (dynamic allocation, $O(1)$ move, can be resized, resizing may invalidate iterators). Other people may want other contiguous containers with different properties (e.g., array with its compile-time size and aggregate initialization, or static_vector with its compile-time capacity but run-time size), but span can represent a view of any of these. Similarly, mdspan can represent just about any multidimensional array view (it doesn't even require that elements exist in memory, let alone that the memory be contiguous), while mdarray covers the more specific use case of multidimensional arrays with an underlying contiguous container. Just as vector doesn't serve all contiguous container use cases, mdarray doesn't serve all multidimensional array container use cases. However, mdspan can view the elements of just about any multidimensional array container a user might want to write.