On Fri, Sep 5, 2025 at 2:25 PM Jonathan Wakely <jwak...@redhat.com> wrote:
> On Fri, 5 Sept 2025 at 08:14, Tomasz Kamiński <tkami...@redhat.com> wrote: > > > > From: Luc Grosheintz <luc.groshei...@gmail.com> > > > > This is a partial implementation of P2781R9. It adds std::cw and > > std::constant_wrapper, but doesn't modify __integral_constant_like for > > span/mdspan. > > > > libstdc++-v3/ChangeLog: > > > > * include/bits/version.def (constant_wrapper): Add. > > * include/bits/version.h: Regenerate. > > * include/std/type_traits (_CwFixedValue): New class. > > (_IndexSequence): New struct. > > (_BuildIndexSequence): New struct. > > (_ConstExprParam): New concept. > > (_CwOperators): New struct. > > (constant_wrapper): New struct. > > (cw): New global constant. > > * src/c++23/std.cc.in (constant_wrapper): Add. > > (cw): Add. > > * testsuite/20_util/constant_wrapper/adl.cc: New test. > > * testsuite/20_util/constant_wrapper/ex.cc: New test. > > * testsuite/20_util/constant_wrapper/generic.cc: New test. > > * testsuite/20_util/constant_wrapper/instantiate.cc: New test. > > * testsuite/20_util/constant_wrapper/op_comma_neg.cc: New test. > > * testsuite/20_util/constant_wrapper/version.cc: New test. > > > > Co-authored-by: Tomasz Kamiński <tkami...@redhat.com> > > Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com> > > Signed-off-by: Tomasz Kamiński <tkami...@redhat.com> > > --- > > v5 adds data member pointer tests > > This adds a lot of new code to <type_traits> which needs to be > preprocessed even by C++11/14/17/20/23 programs, so we might want to > put it in a separate header that is included from <type_traits> > conditionally: > #ifdef __cpp_lib_constant_wrapper > #include <bits/constant_wrapper.h> > #endif > but we can do that later, as splitting up <type_traits> is already > planned (maybe we should look into that for GCC 16 during stage 3, > when we're stabilising things). > I have raised this during review of the patch https://gcc.gnu.org/pipermail/libstdc++/2025-September/063202.html. Luc pointed out that would need to also move _Build_index_type somewhere where it can be included from the new file, or just assume it is declared before including `bits/constant_wrapper` (i.e. included in the middle of the file). This convinced me that this is something we should take into consideration when splitting type_traits. > > OK for trunk, thank you both for working on this. > >
