Merge 2023-02 LWG Motion 20

P2763R1 layout_stride static extents default constructor fix

Author: tkoeppe

source/containers.tex

@@ -19819,7 +19819,7 @@
 
   public:
     // \ref{mdspan.layout.stride.cons}, constructors
-    constexpr mapping() noexcept = default;
+    constexpr mapping() noexcept;
     constexpr mapping(const mapping&) noexcept = default;
     template<class OtherIndexType>
       constexpr mapping(const extents_type&, span<OtherIndexType, @\exposid{rank_}@>) noexcept;
@@ -19937,6 +19937,25 @@
 
 \rSec5[mdspan.layout.stride.cons]{Constructors}
 
+\indexlibraryctor{layout_stride::mapping}%
+\begin{itemdecl}
+constexpr mapping() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\expects
+\tcode{layout_right::mapping<extents_type>().required_span_size()}
+is representable as a value of type \tcode{index_type}\iref{basic.fundamental}.
+
+\pnum
+\effects
+Direct-non-list-initializes \exposid{extents_} with \tcode{extents_type()}, and
+for all $d$ in the range \range{0}{\exposid{rank_}},
+direct-non-list-initializes \tcode{\exposid{strides_}[$d$]} with
+\tcode{layout_right::mapping<extents_type>().stride($d$)}.
+\end{itemdescr}
+
 \indexlibraryctor{layout_stride::mapping}%
 \begin{itemdecl}
 template<class OtherIndexType>