Issue 4275 - WG21 LWG Issues
Title
`std::dynamic_extent` should also be defined in <mdspan>
Status
wp
Section
[mdspan.syn]
Submitter
Aiden Grossman

Created on 2025-06-06.00:00:00 last changed 5 days ago

Messages

msg15625 (view)
Date: 2025-11-11.10:48:16

Proposed resolution:

This wording is relative to N5008.

  1. Modify [views.general] as indicated:

    The header <span> ([span.syn]) defines the view `span`. The header <mdspan> ([mdspan.syn]) defines the class template `mdspan` and other facilities for interacting with these multidimensional views.

    -?- In addition to being available via inclusion of the <span> header, `dynamic_extent` is available when the header <mdspan> is included.

msg15217 (view)
Date: 2025-11-11.10:48:16

[ Kona 2025-11-08; Status changed: Voting → WP. ]
msg15180 (view)
Date: 2025-10-15.00:00:00

[ 2025-10-17; Reflector poll. ]

Set status to Tentatively Ready after eight votes in favour during reflector poll.

msg14786 (view)
Date: 2025-10-15.00:00:00

[ 2025-10-15; Reflector poll ]

Set priority to 3 after reflector poll.

msg14785 (view)
Date: 2025-06-15.00:00:00

[ 2025-06-10; Jonathan provides improved wording ]
msg14784 (view)
Date: 2025-06-10.09:34:04

`std::dynamic_extent` can be used in certain circumstances in `std::mdspan`, such as with padded layouts. However, `std::dynamic_extent` is currently only defined in <span> which necessitates including <span> solely for the `std::dynamic_extent` definition.

This wording is relative to N5008.

  1. Modify [mdspan.syn], header <span> synopsis, as indicated:

    // all freestanding
namespace std {
  // constants
  inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
  
  // [mdspan.extents], class template extents
  template<class IndexType, size_t... Extents>
  class extents;

  […]
}
History
Date User Action Args
2025-11-11 10:48:16adminsetmessages: + msg15625
2025-11-11 10:48:16adminsetstatus: voting -> wp
2025-10-30 17:45:31adminsetstatus: ready -> voting
2025-10-17 13:18:18adminsetmessages: + msg15217
2025-10-17 13:18:18adminsetstatus: new -> ready
2025-10-16 11:35:46adminsetmessages: + msg15180
2025-06-10 09:34:04adminsetmessages: + msg14786
2025-06-07 14:02:46adminsetmessages: + msg14785
2025-06-06 00:00:00admincreate