Hi! r16-442 implemented both std::extents and std::dextents (and perhaps other stuff), but exported only std::extents. I went through https://eel.is/c++draft/mdspan.syn and I think std::dextents is the only one implemented but not exported.
The following patch exports it, and additionally appends some further entities to the FIXME list, those all seems to be unimplemented yet. Tested on x86_64-linux, ok for trunk? 2025-07-19 Jakub Jelinek <ja...@redhat.com> PR libstdc++/121174 * src/c++23/std.cc.in (std::dextents): Export. Add to FIXME comments other not yet implemented nor exported <mdspan> entities. --- libstdc++-v3/src/c++23/std.cc.in.jj 2025-07-19 14:39:32.617034910 +0200 +++ libstdc++-v3/src/c++23/std.cc.in 2025-07-19 14:41:32.641471785 +0200 @@ -1850,12 +1850,15 @@ export namespace std export namespace std { using std::extents; + using std::dextents; using std::layout_left; using std::layout_right; using std::layout_stride; using std::default_accessor; using std::mdspan; - // FIXME layout_left_padded, layout_right_padded, aligned_accessor, mdsubspan + // FIXME layout_left_padded, layout_right_padded, aligned_accessor, + // strided_slice, submdspan_mapping_result, full_extent_t, full_extent, + // submdspan_extents, mdsubspan } #endif Jakub