On Tue, Jul 15, 2025 at 12:56 PM Luc Grosheintz <luc.groshei...@gmail.com> wrote:
> > > On 7/14/25 08:57, Tomasz Kaminski wrote: > > Hi Luc, > > > > While running the libc++ test on libstdc++ we have found the following > > issue in our implementation. > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121061 > > Would you be interested in looking into fixing this? > > Yes, I'll take care of this. Do you know if it's the only issue? > If it's not clear it might make sense that I learn how to run their > tests on our code. > > > > > Also, libc++ makes the default constructor of mdpsan conditionally > noexcept > > as extension > > (standard does not require it > > https://eel.is/c++draft/views.multidim#mdspan.mdspan.cons). > > We could do the same. Instead of writing a big conditional noexcept > > specification, I would suggest > > defaultint the constructor on first declaration: > > constexpr > > mdspan() > > requires (rank_dynamic() > 0) > > && is_default_constructible_v<data_handle_type> > > && is_default_constructible_v<mapping_type> > > && is_default_constructible_v<accessor_type> > > = default; > > > > And then having default member initializers: > > private: > > [[no_unique_address]] accessor_type _M_accessor = accessor_type(); > > [[no_unique_address]] mapping_type _M_mapping = mapping_type(); > > [[no_unique_address]] data_handle_type _M_handle = > data_handle_type(); > > We do not want to use "{}" as the samantis is a bit differnt. > > > > Yes, I think it makes sense if those two implementations behave > the same. > It seem that clang defines mdspan::is_(always_)?(exhaustive|unique|strided) with conditional noexcept. Given that standard-provided layouts define this funciton as noexcept, it makes sense to propagate that, for common cases.
