On Tue, May 26, 2026 at 11:33 AM Jonathan Wakely <[email protected]> wrote:
> On Wed, 20 May 2026 at 13:18 +0200, 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. > > "dereference" and "known" > > >Similary for ref_view<R>::empty() we compare the size with zero, > >if it is know statically. > > "known" > > > > >This implements revelant part of P3928R0: static_sized_range by Hewill > Kang. > > "relevant" > > >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) > > I think Patrick asked for the names _Range and __r, which I think > would be a small improvement, but it would make the return statements > even longer. > I already made that change locally, when I saw his request, so I will be merging to trunk with it. > > OK for trunk with or without that change. > > >+ { > >+ if constexpr (ranges::size(__t) <= size_t(-1)) > > I was going to say I would have used -1zu here, but maybe being > explicit about size_t makes sense, to match the next line: > > >+ 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 > > > > 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 > > > > > >
