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.
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
