This implements P1739R4 along with the resolution for LWG 3407 which
corrects the paper's wording.
Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
libstdc++-v3/ChangeLog:
* include/bits/ranges_util.h (views::_Drop): Forward declare.
(subrange): Befriend views::_Drop.
(subrange::_S_store_size): Declare constexpr instead of just
const, remove obsolete comment.
* include/std/ranges (views::__detail::__is_empty_view): Define.
(views::__detail::__is_basic_string_view): Likewise.
(views::__detail::__is_subrange): Likewise.
(views::__detail::__is_iota_view): Likewise.
(views::__detail::__can_take_view): Rename template parm _Tp to _Dp.
(views::_Take): Rename template parm _Tp to _Dp, make it non-deducible
and fix its type to range_difference_t<_Range>. Implement P1739R4 and
LWG 3407 changes.
(views::__detail::__can_drop_view): Rename template parm _Tp to _Dp.
(views::_Drop): As with views::_Take.
(views::_Counted): Implement P1739R4 changes.
* include/std/span (__detail::__is_std_span): Rename to ...
(__detail::__is_span): ... this and turn it into a variable
template.
(__detail::__is_std_array): Turn it into a variable template.
(span::span): Adjust uses of __is_std_span and __is_std_array
accordingly.
* testsuite/std/ranges/adaptors/p1739.cc: New test.
---
libstdc++-v3/include/bits/ranges_util.h | 7 +-
libstdc++-v3/include/std/ranges | 106 +++++++++++++++---
libstdc++-v3/include/std/span | 12 +-
.../testsuite/std/ranges/adaptors/p1739.cc | 88 +++++++++++++++
4 files changed, 192 insertions(+), 21 deletions(-)
create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/p1739.cc
diff --git a/libstdc++-v3/include/bits/ranges_util.h
b/libstdc++-v3/include/bits/ranges_util.h
index 7e7b958d274..1afa66d298c 100644
--- a/libstdc++-v3/include/bits/ranges_util.h
+++ b/libstdc++-v3/include/bits/ranges_util.h
@@ -211,6 +211,8 @@ namespace ranges
} // namespace __detail
+ namespace views { struct _Drop; }
+
enum class subrange_kind : bool { unsized, sized };
/// The ranges::subrange class template
@@ -221,8 +223,9 @@ namespace ranges
class subrange : public view_interface<subrange<_It, _Sent, _Kind>>
{
private:
- // XXX: gcc complains when using constexpr here
- static const bool _S_store_size
+ friend struct views::_Drop; // Needs to inspect _S_store_size.
+
+ static constexpr bool _S_store_size
= _Kind == subrange_kind::sized && !sized_sentinel_for<_Sent, _It>;
_It _M_begin = _It();
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 85f232d8fb9..64396027c1b 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -42,6 +42,7 @@
#include <initializer_list>
#include <iterator>
#include <optional>
+#include <span>
#include <tuple>
#include <bits/ranges_util.h>
#include <bits/refwrap.h>
@@ -2147,19 +2148,66 @@ namespace views::__adaptor
{
namespace __detail
{
- template<typename _Range, typename _Tp>
+ template<typename _Range>
+ constexpr bool __is_empty_view = false;
+
+ template<typename _Tp>
+ constexpr bool __is_empty_view<empty_view<_Tp>> = true;
+
+ template<typename _Range>
+ constexpr bool __is_basic_string_view = false;
+
+ template<typename _CharT, typename _Traits>
+ constexpr bool __is_basic_string_view<basic_string_view<_CharT,
_Traits>> = true;
+
+ template<typename _Range>
+ constexpr bool __is_subrange = false;
+
+ template<typename _Iter, typename _Sent, subrange_kind _Kind>
+ constexpr bool __is_subrange<subrange<_Iter, _Sent, _Kind>> = true;
+
+ template<typename _Range>
+ constexpr bool __is_iota_view = false;
+
+ template<typename _Winc, typename _Bound>
+ constexpr bool __is_iota_view<iota_view<_Winc, _Bound>> = true;
+
+ template<typename _Range, typename _Dp>
concept __can_take_view
- = requires { take_view(std::declval<_Range>(), std::declval<_Tp>());
};
+ = requires { take_view(std::declval<_Range>(), std::declval<_Dp>());
};
} // namespace __detail
struct _Take : __adaptor::_RangeAdaptor<_Take>
{
- template<viewable_range _Range, typename _Tp>
- requires __detail::__can_take_view<_Range, _Tp>
+ template<viewable_range _Range, typename _Dp =
range_difference_t<_Range>>
+ requires __detail::__can_take_view<_Range, _Dp>
constexpr auto
- operator() [[nodiscard]] (_Range&& __r, _Tp&& __n) const
+ operator() [[nodiscard]] (_Range&& __r, type_identity_t<_Dp> __n) const
{
- return take_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
+ using _Tp = remove_cvref_t<_Range>;
+ if constexpr (__detail::__is_empty_view<_Tp>)
+ return _Tp();
+ else if constexpr (random_access_range<_Tp>
+ && sized_range<_Tp>
+ && (std::__detail::__is_span<_Tp>
+ || __detail::__is_basic_string_view<_Tp>
+ || __detail::__is_subrange<_Tp>
+ || __detail::__is_iota_view<_Tp>))
+ {
+ __n = std::min<_Dp>(ranges::distance(__r), __n);
+ auto __begin = ranges::begin(__r);
+ auto __end = __begin + __n;
+ if constexpr (std::__detail::__is_span<_Tp>)
+ return span<typename _Tp::element_type>(__begin, __end);
+ else if constexpr (__detail::__is_basic_string_view<_Tp>)
+ return _Tp(__begin, __end);
+ else if constexpr (__detail::__is_subrange<_Tp>)
+ return subrange<iterator_t<_Tp>>(__begin, __end);
+ else
+ return iota_view(*__begin, *__end);
+ }
+ else
+ return take_view(std::forward<_Range>(__r), __n);
}
using _RangeAdaptor<_Take>::operator();
@@ -2394,19 +2442,49 @@ namespace views::__adaptor
{
namespace __detail
{
- template<typename _Range, typename _Tp>
+ template<typename _Range, typename _Dp>
concept __can_drop_view
- = requires { drop_view(std::declval<_Range>(), std::declval<_Tp>());
};
+ = requires { drop_view(std::declval<_Range>(), std::declval<_Dp>());
};
} // namespace __detail
struct _Drop : __adaptor::_RangeAdaptor<_Drop>
{
- template<viewable_range _Range, typename _Tp>
- requires __detail::__can_drop_view<_Range, _Tp>
+ template<viewable_range _Range, typename _Dp =
range_difference_t<_Range>>
+ requires __detail::__can_drop_view<_Range, _Dp>
constexpr auto
- operator() [[nodiscard]] (_Range&& __r, _Tp&& __n) const
+ operator() [[nodiscard]] (_Range&& __r, type_identity_t<_Dp> __n) const
{
- return drop_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
+ using _Tp = remove_cvref_t<_Range>;
+ if constexpr (__detail::__is_empty_view<_Tp>)
+ return _Tp();
+ else if constexpr (random_access_range<_Tp>
+ && sized_range<_Tp>
+ && (std::__detail::__is_span<_Tp>
+ || __detail::__is_basic_string_view<_Tp>
+ || __detail::__is_iota_view<_Tp>
+ || __detail::__is_subrange<_Tp>))
+ {
+ __n = std::min<_Dp>(ranges::distance(__r), __n);
+ auto __begin = ranges::begin(__r) + __n;
+ auto __end = ranges::end(__r);
+ if constexpr (std::__detail::__is_span<_Tp>)
+ return span<typename _Tp::element_type>(__begin, __end);
+ else if constexpr (__detail::__is_subrange<_Tp>)
+ {
+ if constexpr (_Tp::_S_store_size)
+ {
+ using ranges::__detail::__to_unsigned_like;
+ auto __m = ranges::distance(__r) - __n;
+ return _Tp(__begin, __end, __to_unsigned_like(__m));
+ }
+ else
+ return _Tp(__begin, __end);
+ }
+ else
+ return _Tp(__begin, __end);
+ }
+ else
+ return drop_view(std::forward<_Range>(__r), __n);
}
using _RangeAdaptor<_Drop>::operator();
@@ -3536,7 +3614,9 @@ namespace views::__adaptor
constexpr auto
operator() [[nodiscard]] (_Iter __i, iter_difference_t<_Iter> __n) const
{
- if constexpr (random_access_iterator<_Iter>)
+ if constexpr (contiguous_iterator<_Iter>)
+ return span(std::__to_address(__i), __n);
+ else if constexpr (random_access_iterator<_Iter>)
return subrange(__i, __i + __n);
else
return subrange(counted_iterator(std::move(__i), __n),
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index af0d24b29f2..ba75a497310 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -58,16 +58,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace __detail
{
template<typename _Tp>
- struct __is_std_span : false_type { };
+ constexpr bool __is_span = false;
template<typename _Tp, size_t _Num>
- struct __is_std_span<span<_Tp, _Num>> : true_type { };
+ constexpr bool __is_span<span<_Tp, _Num>> = true;
template<typename _Tp>
- struct __is_std_array : false_type { };
+ constexpr bool __is_std_array = false;
template<typename _Tp, size_t _Num>
- struct __is_std_array<std::array<_Tp, _Num>> : true_type { };
+ constexpr bool __is_std_array<std::array<_Tp, _Num>> = true;
template<size_t _Extent>
class __extent_storage
@@ -203,8 +203,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Range>
requires ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
&& (ranges::borrowed_range<_Range> || is_const_v<element_type>)
- && (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
- && (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
+ && (!__detail::__is_span<remove_cvref_t<_Range>>)
+ && (!__detail::__is_std_array<remove_cvref_t<_Range>>)
&& (!is_array_v<remove_cvref_t<_Range>>)
&& __is_compatible_ref<ranges::range_reference_t<_Range>>::value
constexpr explicit(extent != dynamic_extent)
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/p1739.cc
b/libstdc++-v3/testsuite/std/ranges/adaptors/p1739.cc
new file mode 100644
index 00000000000..243b8a03583
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/p1739.cc
@@ -0,0 +1,88 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do run { target c++20 } }
+
+#include <algorithm>
+#include <ranges>
+#include <testsuite_hooks.h>
+
+// Verify P1739R4 (and LWG 3407) changes views::take/drop/counted.
+
+namespace ranges = std::ranges;
+namespace views = ranges::views;
+
+void
+test01()
+{
+ ranges::empty_view<int> v;
+ using ty = decltype(v);
+ using ty = decltype(views::take(v, 42));
+ using ty = decltype(views::drop(v, 42));
+}
+
+void
+test02()
+{
+ int x[] = {1,2,3,4,5};
+ std::span r(x, x+5);
+ using ty = decltype(r);
+
+ std::same_as<ty> auto v1 = views::take(r, 2);
+ VERIFY( ranges::equal(v1, (int[]){1,2}) );
+
+ std::same_as<ty> auto v2 = views::drop(r, 3);
+ VERIFY( ranges::equal(v2, (int[]){4,5}) );
+
+ std::same_as<ty> auto v3 = views::counted(r.begin(), 4);
+ VERIFY( ranges::equal(v3, (int[]){1,2,3,4}) );
+}
+
+void
+test03()
+{
+ using namespace std::literals;
+ std::string_view r = "hello world"sv;
+ using ty = decltype(r);
+
+ std::same_as<ty> auto v1 = views::take(r, 5);
+ VERIFY( ranges::equal(v1, "hello"sv) );
+
+ std::same_as<ty> auto v2 = views::drop(r, 6);
+ VERIFY( ranges::equal(v2, "world"sv) );
+}
+
+void
+test04()
+{
+ int x[] = {1,2,3,4,5};
+ ranges::subrange r(x, x+5);
+ using ty = decltype(r);
+
+ std::same_as<ty> auto v1 = views::take(r, 2);
+ VERIFY( ranges::equal(v1, (int[]){1,2}) );
+
+ std::same_as<ty> auto v2 = views::drop(r, 1);
+ VERIFY( ranges::equal(v2, (int[]){2,3,4,5}) );
+}
+
+void
+test05()
+{
+ auto r1 = views::iota(1, 6);
+ using ty1 = decltype(r1);
+
+ std::same_as<ty1> auto v1 = views::take(r1, 2);
+ VERIFY( ranges::equal(v1, (int[]){1,2}) );
+
+ std::same_as<ty1> auto v2 = views::drop(r1, 3);
+ VERIFY( ranges::equal(v2, (int[]){4,5}) );
+}
+
+int
+main()
+{
+ test01();
+ test02();
+ test03();
+ test04();
+ test05();
+}
--
2.33.1.637.gf443b226ca
