<div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Wed, May 20, 2026 at 12:04 AM 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 Fri, 24 Apr 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>
> v2 also expands the empty() method, and adds __static_size helper funciton.<br>
> We could really use some consteval __builtin_unknown_ref(_Tp), that will<br>
> produce reference to unknown object of type _Tp. This will avoid nested<br>
> lambda and instantiating integer_constant.<br>
> <br>
> Tested on x86_64-linux. OK for trunk?<br>
> <br>
> libstdc++-v3/include/bits/ranges_base.h | 9 +++++++++<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, 31 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..e61ef75f857 100644<br>
> --- a/libstdc++-v3/include/bits/ranges_base.h<br>
> +++ b/libstdc++-v3/include/bits/ranges_base.h<br>
> @@ -562,6 +562,15 @@ 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 not _Tp<br>
<br>
> + consteval range_size_t<_Tp><br>
> + __static_size()<br>
> + {<br>
> + auto __conjure = [](_Tp& __t)<br>
<br>
__r not __t<br>
<br>
> + { return integral_constant<range_size_t<_Tp>, ranges::size(__t)>{}; };<br>
> + return decltype(__conjure(std::declval<_Tp&>()))::value;<br>
> + }<br>
<br>
Maybe we could fix the first parameter of integral_constant to size_t and<br>
cast its value to range_size_t afterwards, which should result in fewer<br>
integral_constant instantiations.<br></blockquote><div>I was hoping I would get a building so I could avoid all of this, created</div><div>ticket: <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125394">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125394</a><br><br></div><div>I need to be careful about ranges with size greater than size_t, but can</div><div>workaround that. Will post new patch soon.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
It might make sense to add another overload that takes a _Range&<br>
parameter to allow the range type to be deduced. And that overload<br>
could be implemented as a one liner return ranges::size(__r).<br>
We could then define <simd>'s __static_range_size in terms of this.<br></blockquote><div>What is the use case you are thinking of? Because if you have _Range&</div><div>object that you can pass, you could invoke ranges::size(__r) directly. </div><div>So unless, I am missing something that sounds like extra indirection,</div><div>that could be avoided.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<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 4f2082487d1..c1e8ac3cb17 100644<br>
> --- a/libstdc++-v3/include/std/ranges<br>
> +++ b/libstdc++-v3/include/std/ranges<br>
> @@ -1380,11 +1380,25 @@ 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>
> 2.53.0<br>
> <br>
> <br>
</blockquote></div></div>