hxie/adjacent transform #168208
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hxie/adjacent transform #168208
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huixie90
commented
Nov 15, 2025
huixie90
commented
- [libc++] implement adjacent_view
- ci
- ci
- [libc++] adjacent_transform
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libc++
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@llvm/pr-subscribers-libcxx Author: Hui (huixie90) Changes
Patch is 269.82 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/168208.diff 66 Files Affected:
diff --git a/libcxx/docs/ReleaseNotes/22.rst b/libcxx/docs/ReleaseNotes/22.rst
index ec23ba9d1e3a1..326da58897dcd 100644
--- a/libcxx/docs/ReleaseNotes/22.rst
+++ b/libcxx/docs/ReleaseNotes/22.rst
@@ -38,8 +38,7 @@ What's New in Libc++ 22.0.0?
Implemented Papers
------------------
-- P2321R2: ``zip`` (`Github <https://llvm.org/PR105169>`__) (The paper is partially implemented. ``zip_transform_view``
- is implemented in this release)
+- P2321R2: ``zip`` (`Github <https://llvm.org/PR105169>`__) (The paper is partially implemented. ``zip_transform_view``, ``adjacent_view``, and ``adjacent_transform_view`` are implemented in this release)
- P3044R2: sub-``string_view`` from ``string`` (`Github <https://llvm.org/PR148140>`__)
- P3223R2: Making ``std::istream::ignore`` less surprising (`Github <https://llvm.org/PR148178>`__)
- P3060R3: Add ``std::views::indices(n)`` (`Github <https://llvm.org/PR148175>`__)
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index ddace8bf8c728..cac0b1285e0bf 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -696,6 +696,8 @@ set(files
__random/uniform_real_distribution.h
__random/weibull_distribution.h
__ranges/access.h
+ __ranges/adjacent_transform_view.h
+ __ranges/adjacent_view.h
__ranges/all.h
__ranges/as_rvalue_view.h
__ranges/chunk_by_view.h
@@ -739,6 +741,7 @@ set(files
__ranges/view_interface.h
__ranges/views.h
__ranges/zip_transform_view.h
+ __ranges/zip_utils.h
__ranges/zip_view.h
__split_buffer
__std_mbstate_t.h
diff --git a/libcxx/include/__ranges/adjacent_transform_view.h b/libcxx/include/__ranges/adjacent_transform_view.h
new file mode 100644
index 0000000000000..fe8defb5cb56f
--- /dev/null
+++ b/libcxx/include/__ranges/adjacent_transform_view.h
@@ -0,0 +1,411 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___RANGES_ADJACENT_TRANSFORM_VIEW_H
+#define _LIBCPP___RANGES_ADJACENT_TRANSFORM_VIEW_H
+
+#include <__config>
+
+#include <__algorithm/min.h>
+#include <__compare/three_way_comparable.h>
+#include <__concepts/constructible.h>
+#include <__concepts/convertible_to.h>
+#include <__concepts/equality_comparable.h>
+#include <__cstddef/size_t.h>
+#include <__functional/invoke.h>
+#include <__functional/operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/iter_move.h>
+#include <__iterator/iter_swap.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
+#include <__iterator/prev.h>
+#include <__memory/addressof.h>
+#include <__ranges/access.h>
+#include <__ranges/adjacent_view.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/empty_view.h>
+#include <__ranges/movable_box.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/size.h>
+#include <__ranges/view_interface.h>
+#include <__ranges/zip_transform_view.h>
+#include <__ranges/zip_utils.h>
+#include <__type_traits/common_type.h>
+#include <__type_traits/is_nothrow_constructible.h>
+#include <__type_traits/is_referenceable.h>
+#include <__type_traits/make_unsigned.h>
+#include <__type_traits/maybe_const.h>
+#include <__utility/declval.h>
+#include <__utility/forward.h>
+#include <__utility/in_place.h>
+#include <__utility/integer_sequence.h>
+#include <__utility/move.h>
+#include <concepts>
+#include <ranges>
+#include <tuple>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+namespace ranges {
+
+template <class _Fn, size_t _Np>
+struct __apply_n {
+ template <class... _Ts>
+ static auto __apply(tuple<_Ts...>&&) -> invoke_result_t<_Fn, _Ts...>;
+
+ template <class _Tp, size_t... _Is>
+ static auto __make_tuple_impl(index_sequence<_Is...>) -> tuple<decltype((_Is, std::declval<_Tp (*)()>()()))...>;
+
+ template <class _Tp>
+ static constexpr auto operator()(_Tp&&) -> decltype(__apply(__make_tuple_impl<_Tp&&>(make_index_sequence<_Np>{})));
+};
+
+template <forward_range _View, move_constructible _Fn, size_t _Np>
+ requires view<_View> && (_Np > 0) && is_object_v<_Fn> &&
+ regular_invocable<__apply_n<_Fn&, _Np>, range_reference_t<_View>> &&
+ __referenceable<invoke_result_t<__apply_n<_Fn&, _Np>, range_reference_t<_View>>>
+class adjacent_transform_view : public view_interface<adjacent_transform_view<_View, _Fn, _Np>> {
+private:
+ _LIBCPP_NO_UNIQUE_ADDRESS adjacent_view<_View, _Np> __inner_;
+ _LIBCPP_NO_UNIQUE_ADDRESS __movable_box<_Fn> __fun_;
+
+ using _InnerView _LIBCPP_NODEBUG = adjacent_view<_View, _Np>;
+
+ template <bool _Const>
+ using __inner_iterator _LIBCPP_NODEBUG = iterator_t<__maybe_const<_Const, _InnerView>>;
+
+ template <bool _Const>
+ using __inner_sentinel _LIBCPP_NODEBUG = sentinel_t<__maybe_const<_Const, _InnerView>>;
+
+ template <bool>
+ class __iterator;
+
+ template <bool>
+ class __sentinel;
+
+public:
+ _LIBCPP_HIDE_FROM_ABI adjacent_transform_view() = default;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr explicit adjacent_transform_view(_View __base, _Fn __fun)
+ : __inner_(std::move(__base)), __fun_(std::in_place, std::move(__fun)) {}
+
+ _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+ requires copy_constructible<_View>
+ {
+ return __inner_.base();
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__inner_).base(); }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto begin() { return __iterator<false>(*this, __inner_.begin()); }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+ requires range<const _InnerView> && regular_invocable<__apply_n<const _Fn&, _Np>, range_reference_t<const _View>>
+ {
+ return __iterator<true>(*this, __inner_.begin());
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto end() {
+ if constexpr (common_range<_InnerView>) {
+ return __iterator<false>(*this, __inner_.end());
+ } else {
+ return __sentinel<false>(__inner_.end());
+ }
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+ requires range<const _InnerView> && regular_invocable<__apply_n<const _Fn&, _Np>, range_reference_t<const _View>>
+ {
+ if constexpr (common_range<const _InnerView>) {
+ return __iterator<true>(*this, __inner_.end());
+ } else {
+ return __sentinel<true>(__inner_.end());
+ }
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+ requires sized_range<_InnerView>
+ {
+ return __inner_.size();
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+ requires sized_range<const _InnerView>
+ {
+ return __inner_.size();
+ }
+};
+
+template <forward_range _View, move_constructible _Fn, size_t _Np>
+ requires view<_View> && (_Np > 0) && is_object_v<_Fn> &&
+ regular_invocable<__apply_n<_Fn&, _Np>, range_reference_t<_View>> &&
+ __referenceable<invoke_result_t<__apply_n<_Fn&, _Np>, range_reference_t<_View>>>
+template <bool _Const>
+class adjacent_transform_view<_View, _Fn, _Np>::__iterator {
+ friend adjacent_transform_view;
+
+ using _Parent _LIBCPP_NODEBUG = __maybe_const<_Const, adjacent_transform_view>;
+ using _Base _LIBCPP_NODEBUG = __maybe_const<_Const, _View>;
+
+ _Parent* __parent_ = nullptr;
+ __inner_iterator<_Const> __inner_;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator(_Parent& __parent, __inner_iterator<_Const> __inner)
+ : __parent_(std::addressof(__parent)), __inner_(std::move(__inner)) {}
+
+ static consteval auto __get_iterator_category() {
+ using _Cat = iterator_traits<iterator_t<_Base>>::iterator_category;
+ if constexpr (!is_reference_v<
+ invoke_result_t<__apply_n<__maybe_const<_Const, _Fn>&, _Np>, range_reference_t<_Base>>>)
+ return input_iterator_tag{};
+ else if constexpr (derived_from<_Cat, random_access_iterator_tag>)
+ return random_access_iterator_tag{};
+ else if constexpr (derived_from<_Cat, bidirectional_iterator_tag>)
+ return bidirectional_iterator_tag{};
+ else if constexpr (derived_from<_Cat, forward_iterator_tag>)
+ return forward_iterator_tag{};
+ else
+ return input_iterator_tag{};
+ }
+
+ template <size_t... _Is>
+ static consteval bool __noexcept_dereference(index_sequence<_Is...>) {
+ return noexcept(std::invoke(
+ std::declval<__maybe_const<_Const, _Fn>&>(),
+ *std::get<_Is>(
+ __adjacent_view_iter_access::__get_current(std::declval<const __inner_iterator<_Const>&>()))...));
+ }
+
+public:
+ using iterator_category = decltype(__get_iterator_category());
+ using iterator_concept = typename __inner_iterator<_Const>::iterator_concept;
+ using value_type =
+ remove_cvref_t<invoke_result_t<__apply_n<__maybe_const<_Const, _Fn>&, _Np>, range_reference_t<_Base>>>;
+ using difference_type = range_difference_t<_Base>;
+
+ _LIBCPP_HIDE_FROM_ABI __iterator() = default;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator(__iterator<!_Const> __i)
+ requires _Const && convertible_to<__inner_iterator<false>, __inner_iterator<true>>
+ : __parent_(__i.__parent_), __inner_(std::move(__i.__inner_)) {}
+
+ _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const
+ noexcept(__noexcept_dereference(make_index_sequence<_Np>{})) {
+ return std::apply(
+ [&](const auto&... __iters) -> decltype(auto) { return std::invoke(*__parent_->__fun_, *__iters...); },
+ __adjacent_view_iter_access::__get_current(__inner_));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator++() {
+ ++__inner_;
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator operator++(int) {
+ auto __tmp = *this;
+ ++*this;
+ return __tmp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator--()
+ requires bidirectional_range<_Base>
+ {
+ --__inner_;
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator operator--(int)
+ requires bidirectional_range<_Base>
+ {
+ auto __tmp = *this;
+ --*this;
+ return __tmp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator+=(difference_type __x)
+ requires random_access_range<_Base>
+ {
+ __inner_ += __x;
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __iterator& operator-=(difference_type __x)
+ requires random_access_range<_Base>
+ {
+ __inner_ -= __x;
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator[](difference_type __n) const
+ requires random_access_range<_Base>
+ {
+ return std::apply(
+ [&](const auto&... __iters) -> decltype(auto) { return std::invoke(*__parent_->__fun_, __iters[__n]...); },
+ __adjacent_view_iter_access::__get_current(__inner_));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const __iterator& __x, const __iterator& __y) {
+ return __x.__inner_ == __y.__inner_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<(const __iterator& __x, const __iterator& __y)
+ requires random_access_range<_Base>
+ {
+ return __x.__inner_ < __y.__inner_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>(const __iterator& __x, const __iterator& __y)
+ requires random_access_range<_Base>
+ {
+ return __x.__inner_ > __y.__inner_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<=(const __iterator& __x, const __iterator& __y)
+ requires random_access_range<_Base>
+ {
+ return __x.__inner_ <= __y.__inner_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>=(const __iterator& __x, const __iterator& __y)
+ requires random_access_range<_Base>
+ {
+ return __x.__inner_ >= __y.__inner_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr auto operator<=>(const __iterator& __x, const __iterator& __y)
+ requires random_access_range<_Base> && three_way_comparable<__inner_iterator<_Const>>
+ {
+ return __x.__inner_ <=> __y.__inner_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(const __iterator& __i, difference_type __n)
+ requires random_access_range<_Base>
+ {
+ return __iterator(*__i.__parent_, __i.__inner_ + __n);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator+(difference_type __n, const __iterator& __i)
+ requires random_access_range<_Base>
+ {
+ return __iterator(*__i.__parent_, __i.__inner_ + __n);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr __iterator operator-(const __iterator& __i, difference_type __n)
+ requires random_access_range<_Base>
+ {
+ return __iterator(*__i.__parent_, __i.__inner_ - __n);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const __iterator& __x, const __iterator& __y)
+ requires sized_sentinel_for<__inner_iterator<_Const>, __inner_iterator<_Const>>
+ {
+ return __x.__inner_ - __y.__inner_;
+ }
+};
+
+template <forward_range _View, move_constructible _Fn, size_t _Np>
+ requires view<_View> && (_Np > 0) && is_object_v<_Fn> &&
+ regular_invocable<__apply_n<_Fn&, _Np>, range_reference_t<_View>> &&
+ __referenceable<invoke_result_t<__apply_n<_Fn&, _Np>, range_reference_t<_View>>>
+template <bool _Const>
+class adjacent_transform_view<_View, _Fn, _Np>::__sentinel {
+ friend adjacent_transform_view;
+
+ __inner_sentinel<_Const> __inner_;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr explicit __sentinel(__inner_sentinel<_Const> __inner)
+ : __inner_(std::move(__inner)) {}
+
+public:
+ _LIBCPP_HIDE_FROM_ABI __sentinel() = default;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __sentinel(__sentinel<!_Const> __i)
+ requires _Const && convertible_to<__inner_sentinel<false>, __inner_sentinel<_Const>>
+ : __inner_(std::move(__i.__inner_)) {}
+
+ template <bool _OtherConst>
+ requires sentinel_for<__inner_sentinel<_Const>, __inner_iterator<_OtherConst>>
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const __iterator<_OtherConst>& __x, const __sentinel& __y) {
+ return __x.__inner_ == __y.__inner_;
+ }
+
+ template <bool _OtherConst>
+ requires sized_sentinel_for<__inner_sentinel<_Const>, __inner_iterator<_OtherConst>>
+ _LIBCPP_HIDE_FROM_ABI friend constexpr range_difference_t<__maybe_const<_OtherConst, _InnerView>>
+ operator-(const __iterator<_OtherConst>& __x, const __sentinel& __y) {
+ return __x.__inner_ - __y.__inner_;
+ }
+
+ template <bool _OtherConst>
+ requires sized_sentinel_for<__inner_sentinel<_Const>, __inner_iterator<_OtherConst>>
+ _LIBCPP_HIDE_FROM_ABI friend constexpr range_difference_t<__maybe_const<_OtherConst, _InnerView>>
+ operator-(const __sentinel& __x, const __iterator<_OtherConst>& __y) {
+ return __x.__inner_ - __y.__inner_;
+ }
+};
+
+namespace views {
+namespace __adjacent_transform {
+
+template <size_t _Np>
+struct __fn : __range_adaptor_closure<__fn<_Np>> {
+ template <class _Range, class _Fn>
+ requires(_Np == 0 && forward_range<_Range &&>)
+ _LIBCPP_HIDE_FROM_ABI static constexpr auto
+ operator()(_Range&&, _Fn&& __fn) noexcept(noexcept(views::zip_transform(std::forward<_Fn>(__fn))))
+ -> decltype(views::zip_transform(std::forward<_Fn>(__fn))) {
+ return views::zip_transform(std::forward<_Fn>(__fn));
+ }
+
+ template <class _Range, class _Fn>
+ _LIBCPP_HIDE_FROM_ABI static constexpr auto operator()(_Range&& __range, _Fn&& __fn) noexcept(
+ noexcept(adjacent_transform_view<views::all_t<_Range&&>, decay_t<_Fn>, _Np>(
+ std::forward<_Range>(__range), std::forward<_Fn>(__fn))))
+ -> decltype(adjacent_transform_view<views::all_t<_Range&&>, decay_t<_Fn>, _Np>(
+ std::forward<_Range>(__range), std::forward<_Fn>(__fn))) {
+ return adjacent_transform_view<views::all_t<_Range&&>, decay_t<_Fn>, _Np>(
+ std::forward<_Range>(__range), std::forward<_Fn>(__fn));
+ }
+
+ template <class _Fn>
+ requires constructible_from<decay_t<_Fn>, _Fn>
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Fn&& __f) const
+ noexcept(is_nothrow_constructible_v<decay_t<_Fn>, _Fn>) {
+ return __pipeable(std::__bind_back(*this, std::forward<_Fn>(__f)));
+ }
+};
+
+} // namespace __adjacent_transform
+inline namespace __cpo {
+template <size_t _Np>
+inline constexpr auto adjacent_transform = __adjacent_transform::__fn<_Np>{};
+inline constexpr auto pairwise_transform = adjacent_transform<2>;
+} // namespace __cpo
+} // namespace views
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___RANGES_ADJACENT_TRANSFORM_VIEW_H
diff --git a/libcxx/include/__ranges/adjacent_view.h b/libcxx/include/__ranges/adjacent_view.h
new file mode 100644
index 0000000000000..9eefe4020925e
--- /dev/null
+++ b/libcxx/include/__ranges/adjacent_view.h
@@ -0,0 +1,416 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___RANGES_ADJACENT_VIEW_H
+#define _LIBCPP___RANGES_ADJACENT_VIEW_H
+
+#include <__config>
+
+#include <__algorithm/min.h>
+#include <__compare/three_way_comparable.h>
+#include <__concepts/constructible.h>
+#include <__concepts/convertible_to.h>
+#include <__concepts/equality_comparable.h>
+#include <__cstddef/size_t.h>
+#include <__functional/invoke.h>
+#include <__functional/operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/iter_move.h>
+#include <__iterator/iter_swap.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
+#include <__iterator/prev.h>
+#include <__ranges/access.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/empty_view.h>
+#include <__ranges/enable_borrowed_range.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/size.h>
+#include <__ranges/view_interface.h>
+#include <__ranges/zip_utils.h>
+#include <__type_traits/common_type.h>
+#include <__type_traits/is_nothrow_constructible.h>
+#include <__type_traits/make_unsigned.h>
+#include <__type_traits/maybe_const.h>
+#include <__utility/declval.h>
+#include <__utility/forward.h>
+#include <__utility/integer_sequence.h>
+#include <__utility/move.h>
+#include <array>
+#include <tuple>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+namespace ranges {
+
+template <forward_range _View, size_t _Np>
+ requires view<_View> && (_Np > 0)
+class adjacent_view : public view_interface<adjacent_view<_View, _Np>> {
+private:
+ _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
+
+ template <bool>
+ class __iterator;
+
+ template <bool>
+ class __sentinel;
+
+ struct __as_sentinel {};
+
+public:
+ _LIBCPP_HIDE_FROM_ABI adjacent_view()
+ requires default_initializable<_View>
+ = default;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr explicit adjacent_view(_View __base) : __base_(std::move(__base)) {}
+
+ _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+ requires copy_constructible<_View>
+ {
+ return __base_;
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
+ requires(!__simple_view<_View>)
+ {
+ return __iterator<false>(ranges::begin(__base_), ranges::end(__base_));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+ requires range<const _View> // todo: this seems under-constrained. lwg issue?
+ {
+ return __iterator<true>(ranges::begin(__base_), ranges::end(__base_));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+ requires(!__simple_view<_View>)
+ {
+ if constexpr (common_range<_View>) {
+ return __iterator<false>(__as_sentinel{}, ranges::begin(__base_), ...
[truncated]
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