P1673R12: Varna 2023 LWG review comments

Varna 2023 LWG review comments

2023/06/14

"your matrix_layout_policy isn’t a layout_policy because the latter needs to support any extent" -- not clear whether this is an action item.

2023/06/15

Change to mdspan's specification, not to P1673?

A possible problematic interpretation of [mdspan.layout.policy.reqmts]. Suggested edit: A type MP meets the layout mapping policy requirements if for a type E that is a specialization of extents such that MP::mapping<E> is valid, MP::mapping<E> denotes a type X that meets the layout mapping requirements ([mdspan.layout.reqmts]), and for which the qualified-id X::layout_type is valid and denotes the type MP and the qualified-id X::extents_type denotes E.

TODO list

• Remove reference to P2642R2. P1673 is orthogonal to P2642.
• Change the exposition-only is-mdspan to be a variable template.
• Change "it will do so in read-only fashion" to "it does so ...."
• Implement changes in https://github.com/ORNL/cpp-proposals-pub/issues/390
  • Fix in-vector (and analogous exposition-only concepts) declaration
  • Fix "xT"
  • Figure out what wording LWG wants for abs, conj, imag, and real

Start by reviewing the P1673R12 wording around the mdspan layout policy requirements and the TODO list in this issue. Then inspect issue 390 for the linked changes, including the exposition-only concepts and wording questions for abs, conj, imag, and real. Done means the listed review items are resolved or explicitly dispositioned.