On Wed, May 20, 2026 at 1:20 PM Tomasz Kamiński <[email protected]> wrote:
> This patch introduces ranges::__static_size<_Range> helper functions, > that returns ranges::size(__rg) for __statically_sized_range. > This function is then used for ref_view<R>::size if R has static size, > avoiding derefence of pointer value that is not know at compile time. > Similary for ref_view<R>::empty() we compare the size with zero, > if it is know statically. > > This implements revelant part of P3928R0: static_sized_range by Hewill > Kang. > As standard does not specify when constexpr functions are usable at compile > time, such implementation are allowed (but not mandated) by current draft. > > libstdc++-v3/ChangeLog: > > * include/bits/ranges_base.h (ranges::__static_size): Define. > * include/std/ranges (ref_view::size()): For ranges with static > size return ranges::__static_size<_Range> == 0. > (ref_view::empty): For ranges with static size, compare it > against zero. > * testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc: > Expect errors from ref_view uses. > * testsuite/23_containers/inplace_vector/cons/from_range_neg.cc: > Expect errors from ref_view uses. > > Reviewed-by: Patrick Palka <[email protected]> > Signed-off-by: Tomasz Kamiński <[email protected]> > --- > v3 uses __conjures integral_constant<size_t, for all ranges whose size > fits insize of size_t, regardless of they size_t. > > libstdc++-v3/include/bits/ranges_base.h | 14 ++++++++++++++ > libstdc++-v3/include/std/ranges | 18 ++++++++++++++++-- > .../inplace_vector/cons/from_iota_neg.cc | 6 ++---- > .../inplace_vector/cons/from_range_neg.cc | 10 ++++------ > 4 files changed, 36 insertions(+), 12 deletions(-) > > diff --git a/libstdc++-v3/include/bits/ranges_base.h > b/libstdc++-v3/include/bits/ranges_base.h > index fea4100eb09..bcfaa56fcab 100644 > --- a/libstdc++-v3/include/bits/ranges_base.h > +++ b/libstdc++-v3/include/bits/ranges_base.h > @@ -562,6 +562,20 @@ namespace ranges > template<typename _Tp> > concept __static_sized_range = sized_range<_Tp> && requires (_Tp& __t) > { static_cast<char(*)[size_t(ranges::size(__t) >= 0)]>(nullptr); }; > + > + template<__static_sized_range _Tp> > + consteval range_size_t<_Tp> > + __static_size() > + { > + auto __conjure = [](_Tp& __t) > + { > + if constexpr (ranges::size(__t) <= size_t(-1)) > + return integral_constant<size_t, size_t(ranges::size(__t))>{}; > + else > + return integral_constant<range_size_t<_Tp>, > ranges::size(__t)>{}; > + }; > + return > range_size_t<_Tp>(decltype(__conjure(std::declval<_Tp&>()))::value); > + } > #endif // C++26 > Forgot to mention, the above is supported since clang-21, so it will be covered by the last 3 versions at the time of the GCC-17 release. > > template<typename _Derived> > diff --git a/libstdc++-v3/include/std/ranges > b/libstdc++-v3/include/std/ranges > index 7d8b37f8c5c..2f11cc2336f 100644 > --- a/libstdc++-v3/include/std/ranges > +++ b/libstdc++-v3/include/std/ranges > @@ -1382,11 +1382,25 @@ namespace views::__adaptor > > constexpr bool > empty() const requires requires { ranges::empty(*_M_r); } > - { return ranges::empty(*_M_r); } > + { > +#if __cplusplus > 202302L > + if constexpr (__static_sized_range<_Range>) > + return ranges::__static_size<_Range>() == 0; > + else > +#endif > + return ranges::empty(*_M_r); > + } > > constexpr auto > size() const requires sized_range<_Range> > - { return ranges::size(*_M_r); } > + { > +#if __cplusplus > 202302L > + if constexpr (__static_sized_range<_Range>) > + return ranges::__static_size<_Range>(); > + else > +#endif > + return ranges::size(*_M_r); > + } > > constexpr auto > data() const requires contiguous_range<_Range> > diff --git > a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc > b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc > index ae0b96175b7..6b66b5d97ed 100644 > --- > a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc > +++ > b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc > @@ -33,14 +33,12 @@ test_all() > std::inplace_vector<int, 15> tr1(std::from_range, ref_view(m12)); > > std::inplace_vector<int, 10> tm2(std::from_range, m12); // { dg-error > "(from here|expansion of)" } > - // ref_view is not statically sized due pointer dereference > - std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12)); > + std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12)); // { > dg-error "(from here|expansion of)" } > > StaticIota<__int128, 0> mm; > > std::inplace_vector<int, 10> tm3(std::from_range, mm); // { dg-error > "(from here|expansion of)" } > - // ref_view is not statically sized due pointer dereference > - std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm)); > + std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm)); // { > dg-error "(from here|expansion of)" } > } > > // { dg-error "static assertion failed" "" { target *-*-* } 0 } > diff --git > a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc > b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc > index 48d5b4c56f5..ea187761e5e 100644 > --- > a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc > +++ > b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc > @@ -62,16 +62,14 @@ test_all() > > test_one(a1); // { dg-error "from here" } > test_one(s1); // { dg-error "from here" } > - // ref_view is not statically sized due pointer dereference > - test_one(ref_view(a1)); > - test_one(a5 | std::views::adjacent<7> | std::views::elements<0>); > + test_one(ref_view(a1)); // { dg-error "from here" } > + test_one(a5 | std::views::adjacent<5> | std::views::elements<0>); // { > dg-error "from here" } > test_one(s5 | std::views::adjacent<5> | std::views::elements<0>); // { > dg-error "from here" } > > test_five(a5); // { dg-error "from here" } > test_five(s5); // { dg-error "from here" } > - // ref_view is not statically sized due pointer dereference > - test_five(ref_view(a5)); > - test_five(a7 | std::views::adjacent<3> | std::views::elements<0>); > + test_five(ref_view(a5)); // { dg-error "from here" } > + test_five(a7 | std::views::adjacent<3> | std::views::elements<0>); // { > dg-error "from here" } > test_five(s7 | std::views::adjacent<3> | std::views::elements<0>); // { > dg-error "from here" } > } > > -- > 2.54.0 > >
