While we're modifying elements_view, this also implements the one-line
resolution of LWG 3492.
libstdc++-v3/ChangeLog:
* include/std/ranges (__detail::__returnable_element): New
concept.
(elements_view): Use this concept in its constraints. Add
missing private access specifier.
(elements_view::_S_get_element): Define as per LWG 3502.
(elements_view::operator*, elements_view::operator[]): Use
_S_get_element.
(elements_view::operator++): Remove unnecessary constraint
as per LWG 3492.
* testsuite/std/ranges/adaptors/elements.cc (test05): New test.
---
libstdc++-v3/include/std/ranges | 26 ++++++++++++++++---
.../testsuite/std/ranges/adaptors/elements.cc | 16 ++++++++++++
2 files changed, 38 insertions(+), 4 deletions(-)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 978578197dc..cfcbcaba065 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -3234,6 +3234,10 @@ namespace views::__adaptor
{ std::get<_Nm>(__t) }
-> convertible_to<const tuple_element_t<_Nm, _Tp>&>;
};
+
+ template<typename _Tp, size_t _Nm>
+ concept __returnable_element
+ = is_reference_v<_Tp> || move_constructible<tuple_element_t<_Nm, _Tp>>;
}
template<input_range _Vp, size_t _Nm>
@@ -3241,6 +3245,7 @@ namespace views::__adaptor
&& __detail::__has_tuple_element<range_value_t<_Vp>, _Nm>
&&
__detail::__has_tuple_element<remove_reference_t<range_reference_t<_Vp>>,
_Nm>
+ && __detail::__returnable_element<range_reference_t<_Vp>, _Nm>
class elements_view : public view_interface<elements_view<_Vp, _Nm>>
{
public:
@@ -3298,10 +3303,23 @@ namespace views::__adaptor
template<bool _Const>
struct _Iterator
{
+ private:
using _Base = __detail::__maybe_const_t<_Const, _Vp>;
iterator_t<_Base> _M_current = iterator_t<_Base>();
+ static constexpr decltype(auto)
+ _S_get_element(const iterator_t<_Base>& __i)
+ {
+ if constexpr (is_reference_v<range_reference_t<_Base>>)
+ return std::get<_Nm>(*__i);
+ else
+ {
+ using _Et = remove_cv_t<tuple_element_t<_Nm,
range_reference_t<_Base>>>;
+ return static_cast<_Et>(std::get<_Nm>(*__i));
+ }
+ }
+
friend _Iterator<!_Const>;
public:
@@ -3334,8 +3352,8 @@ namespace views::__adaptor
{ return std::move(_M_current); }
constexpr decltype(auto)
- operator*() const
- { return std::get<_Nm>(*_M_current); }
+ operator*() const
+ { return _S_get_element(_M_current); }
constexpr _Iterator&
operator++()
@@ -3345,7 +3363,7 @@ namespace views::__adaptor
}
constexpr void
- operator++(int) requires (!forward_range<_Base>)
+ operator++(int)
{ ++_M_current; }
constexpr _Iterator
@@ -3390,7 +3408,7 @@ namespace views::__adaptor
constexpr decltype(auto)
operator[](difference_type __n) const
requires random_access_range<_Base>
- { return std::get<_Nm>(*(_M_current + __n)); }
+ { return _S_get_element(_M_current + __n); }
friend constexpr bool
operator==(const _Iterator& __x, const _Iterator& __y)
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc
b/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc
index b0d122f8db5..134afd6a873 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc
@@ -100,6 +100,21 @@ test04()
static_assert(!requires { 0 | elements; });
}
+void
+test05()
+{
+ // LWG 3502
+ std::vector<int> vec = {42};
+ auto r1 = vec
+ | views::transform([](auto c) { return std::make_tuple(c, c); })
+ | views::keys;
+ VERIFY( ranges::equal(r1, (int[]){42}) );
+
+ std::tuple<int, int> a[] = {{1,2},{3,4}};
+ auto r2 = a | views::keys;
+ VERIFY( r2[0] == 1 && r2[1] == 3 );
+}
+
int
main()
{
@@ -107,4 +122,5 @@ main()
test02();
test03();
test04();
+ test05();
}
--
2.31.1.133.g84d06cdc06
