<div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Thu, May 21, 2026 at 2:15 PM Patrick Palka <<a href="mailto:ppalka@redhat.com">ppalka@redhat.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On Wed, 20 May 2026, Tomasz Kamiński wrote:<br>
<br>
> This patch introduces ranges::__static_size<_Range> helper functions,<br>
> that returns ranges::size(__rg) for __statically_sized_range.<br>
> This function is then used for ref_view<R>::size if R has static size,<br>
> avoiding derefence of pointer value that is not know at compile time.<br>
> Similary for ref_view<R>::empty() we compare the size with zero,<br>
> if it is know statically.<br>
> <br>
> This implements revelant part of P3928R0: static_sized_range by Hewill Kang.<br>
> As standard does not specify when constexpr functions are usable at compile<br>
> time, such implementation are allowed (but not mandated) by current draft.<br>
> <br>
> libstdc++-v3/ChangeLog:<br>
> <br>
> * include/bits/ranges_base.h (ranges::__static_size): Define.<br>
> * include/std/ranges (ref_view::size()): For ranges with static<br>
> size return ranges::__static_size<_Range> == 0.<br>
> (ref_view::empty): For ranges with static size, compare it<br>
> against zero.<br>
> * testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc:<br>
> Expect errors from ref_view uses.<br>
> * testsuite/23_containers/inplace_vector/cons/from_range_neg.cc:<br>
> Expect errors from ref_view uses.<br>
> <br>
> Reviewed-by: Patrick Palka <<a href="mailto:ppalka@redhat.com" target="_blank">ppalka@redhat.com</a>><br>
> Signed-off-by: Tomasz Kamiński <<a href="mailto:tkaminsk@redhat.com" target="_blank">tkaminsk@redhat.com</a>><br>
> ---<br>
> v3 uses __conjures integral_constant<size_t, for all ranges whose size<br>
> fits insize of size_t, regardless of they size_t.<br>
> <br>
> libstdc++-v3/include/bits/ranges_base.h | 14 ++++++++++++++<br>
> libstdc++-v3/include/std/ranges | 18 ++++++++++++++++--<br>
> .../inplace_vector/cons/from_iota_neg.cc | 6 ++----<br>
> .../inplace_vector/cons/from_range_neg.cc | 10 ++++------<br>
> 4 files changed, 36 insertions(+), 12 deletions(-)<br>
> <br>
> diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h<br>
> index fea4100eb09..bcfaa56fcab 100644<br>
> --- a/libstdc++-v3/include/bits/ranges_base.h<br>
> +++ b/libstdc++-v3/include/bits/ranges_base.h<br>
> @@ -562,6 +562,20 @@ namespace ranges<br>
> template<typename _Tp><br>
> concept __static_sized_range = sized_range<_Tp> && requires (_Tp& __t)<br>
> { static_cast<char(*)[size_t(ranges::size(__t) >= 0)]>(nullptr); };<br>
> +<br>
> + template<__static_sized_range _Tp><br>
<br>
_Range (for consistency with other helper templates that always take a<br>
range)<br>
<br>
> + consteval range_size_t<_Tp><br>
> + __static_size()<br>
> + {<br>
> + auto __conjure = [](_Tp& __t)<br>
<br>
__r<br></blockquote><div>Changed locally. </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
> + {<br>
> + if constexpr (ranges::size(__t) <= size_t(-1))<br>
> + return integral_constant<size_t, size_t(ranges::size(__t))>{};<br>
> + else<br>
> + return integral_constant<range_size_t<_Tp>, ranges::size(__t)>{}; <br>
<br>
I didn't realize we can only conditionally use integral_constant<size_t<br>
here, probably not worth the added noise since we're likely going to get<br>
the builtin anyway.<br></blockquote><div>It will take some time for clang to get it, so I think it is worth doing. Having</div><div>a statically sized range larger than the maximum value of size_t is very unlikely.</div><div>(We have one in our test).</div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
LGTM etiher way<br>
<br>
> + };<br>
> + return range_size_t<_Tp>(decltype(__conjure(std::declval<_Tp&>()))::value);<br>
> + }<br>
> #endif // C++26<br>
> <br>
> template<typename _Derived><br>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges<br>
> index 7d8b37f8c5c..2f11cc2336f 100644<br>
> --- a/libstdc++-v3/include/std/ranges<br>
> +++ b/libstdc++-v3/include/std/ranges<br>
> @@ -1382,11 +1382,25 @@ namespace views::__adaptor<br>
> <br>
> constexpr bool<br>
> empty() const requires requires { ranges::empty(*_M_r); }<br>
> - { return ranges::empty(*_M_r); }<br>
> + {<br>
> +#if __cplusplus > 202302L<br>
> + if constexpr (__static_sized_range<_Range>)<br>
> + return ranges::__static_size<_Range>() == 0;<br>
> + else<br>
> +#endif<br>
> + return ranges::empty(*_M_r);<br>
> + }<br>
> <br>
> constexpr auto<br>
> size() const requires sized_range<_Range><br>
> - { return ranges::size(*_M_r); }<br>
> + {<br>
> +#if __cplusplus > 202302L<br>
> + if constexpr (__static_sized_range<_Range>)<br>
> + return ranges::__static_size<_Range>();<br>
> + else<br>
> +#endif<br>
> + return ranges::size(*_M_r);<br>
> + }<br>
> <br>
> constexpr auto<br>
> data() const requires contiguous_range<_Range><br>
> 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<br>
> index ae0b96175b7..6b66b5d97ed 100644<br>
> --- a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc<br>
> +++ b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc<br>
> @@ -33,14 +33,12 @@ test_all()<br>
> std::inplace_vector<int, 15> tr1(std::from_range, ref_view(m12));<br>
> <br>
> std::inplace_vector<int, 10> tm2(std::from_range, m12); // { dg-error "(from here|expansion of)" }<br>
> - // ref_view is not statically sized due pointer dereference<br>
> - std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12));<br>
> + std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12)); // { dg-error "(from here|expansion of)" }<br>
> <br>
> StaticIota<__int128, 0> mm;<br>
> <br>
> std::inplace_vector<int, 10> tm3(std::from_range, mm); // { dg-error "(from here|expansion of)" }<br>
> - // ref_view is not statically sized due pointer dereference<br>
> - std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm));<br>
> + std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm)); // { dg-error "(from here|expansion of)" }<br>
> }<br>
> <br>
> // { dg-error "static assertion failed" "" { target *-*-* } 0 }<br>
> 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<br>
> index 48d5b4c56f5..ea187761e5e 100644<br>
> --- a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc<br>
> +++ b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc<br>
> @@ -62,16 +62,14 @@ test_all()<br>
> <br>
> test_one(a1); // { dg-error "from here" }<br>
> test_one(s1); // { dg-error "from here" }<br>
> - // ref_view is not statically sized due pointer dereference<br>
> - test_one(ref_view(a1));<br>
> - test_one(a5 | std::views::adjacent<7> | std::views::elements<0>);<br>
> + test_one(ref_view(a1)); // { dg-error "from here" }<br>
> + test_one(a5 | std::views::adjacent<5> | std::views::elements<0>); // { dg-error "from here" }<br>
> test_one(s5 | std::views::adjacent<5> | std::views::elements<0>); // { dg-error "from here" }<br>
> <br>
> test_five(a5); // { dg-error "from here" }<br>
> test_five(s5); // { dg-error "from here" }<br>
> - // ref_view is not statically sized due pointer dereference<br>
> - test_five(ref_view(a5));<br>
> - test_five(a7 | std::views::adjacent<3> | std::views::elements<0>);<br>
> + test_five(ref_view(a5)); // { dg-error "from here" }<br>
> + test_five(a7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }<br>
> test_five(s7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }<br>
> }<br>
> <br>
> -- <br>
> 2.54.0<br>
> <br>
> <br>
</blockquote></div></div>