On Thu, May 21, 2026 at 2:15 PM Patrick Palka <[email protected]> wrote:
> On Wed, 20 May 2026, Tomasz Kamiński 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> > > _Range (for consistency with other helper templates that always take a > range) > > > + consteval range_size_t<_Tp> > > + __static_size() > > + { > > + auto __conjure = [](_Tp& __t) > > __r > Changed locally. > > > + { > > + 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)>{}; > > I didn't realize we can only conditionally use integral_constant<size_t > here, probably not worth the added noise since we're likely going to get > the builtin anyway. > It will take some time for clang to get it, so I think it is worth doing. Having a statically sized range larger than the maximum value of size_t is very unlikely. (We have one in our test). > > LGTM etiher way > > > + }; > > + return > range_size_t<_Tp>(decltype(__conjure(std::declval<_Tp&>()))::value); > > + } > > #endif // C++26 > > > > 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 > > > > >
