LWG3970 §[mdspan.syn] Missing definition of full_extent_t and full_extent

Author: burblebee

source/containers.tex

@@ -19026,6 +19026,9 @@
   template<class LayoutMapping>
     struct submdspan_mapping_result;
 
+  struct full_extent_t { explicit full_extent_t() = default; };
+  inline constexpr full_extent_t full_extent{};
+
   template<class IndexType, class... Extents, class... SliceSpecifiers>
     constexpr auto submdspan_extents(const extents<IndexType, Extents...>&, SliceSpecifiers...);