================
@@ -0,0 +1,626 @@
+// -*- 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_CONCAT_VIEW_H
+#define _LIBCPP___RANGES_CONCAT_VIEW_H
+
+#include <__algorithm/ranges_find_if.h>
+#include <__assert>
+#include <__concepts/common_reference_with.h>
+#include <__concepts/constructible.h>
+#include <__concepts/convertible_to.h>
+#include <__concepts/copyable.h>
+#include <__concepts/derived_from.h>
+#include <__concepts/equality_comparable.h>
+#include <__concepts/swappable.h>
+#include <__config>
+#include <__functional/bind_back.h>
+#include <__functional/invoke.h>
+#include <__functional/reference_wrapper.h>
+#include <__iterator/concepts.h>
+#include <__iterator/default_sentinel.h>
+#include <__iterator/distance.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 <__memory/addressof.h>
+#include <__ranges/access.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/movable_box.h>
+#include <__ranges/non_propagating_cache.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/size.h>
+#include <__ranges/view_interface.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_nothrow_constructible.h>
+#include <__type_traits/is_nothrow_convertible.h>
+#include <__type_traits/is_object.h>
+#include <__type_traits/make_unsigned.h>
+#include <__type_traits/maybe_const.h>
+#include <__utility/forward.h>
+#include <__utility/in_place.h>
+#include <__utility/move.h>
+#include <tuple>
+#include <variant>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 26
+
+namespace ranges {
+
+template <class _T, class... _Tp>
+struct __extract_last : __extract_last<_Tp...> {};
+
+template <class _T>
+struct __extract_last<_T> {
+ using type = _T;
+};
+
+template <class _T, class... _Tp>
+struct __derived_from_pack {
+ constexpr static bool value =
+ __derived_from_pack<_T, typename __extract_last<_Tp...>::type>::value &&
__derived_from_pack<_Tp...>::value;
+};
+
+template <class _T, class _IterCategory>
+struct __derived_from_pack<_T, _IterCategory> {
+ constexpr static bool value = derived_from<_T, _IterCategory>;
+};
+
+template <class _View, class... _Views>
+struct __last_view : __last_view<_Views...> {};
+
+template <class _View>
+struct __last_view<_View> {
+ using type = _View;
+};
+
+template <class _Ref, class _RRef, class _It>
+concept __concat_indirectly_readable_impl = requires(const _It it) {
+ { *it } -> convertible_to<_Ref>;
+ { ranges::iter_move(it) } -> convertible_to<_RRef>;
+};
+
+template <class... _Rs>
+using __concat_reference_t = common_reference_t<range_reference_t<_Rs>...>;
+
+template <class... _Rs>
+using __concat_value_t = common_type_t<range_value_t<_Rs>...>;
+
+template <class... _Rs>
+using __concat_rvalue_reference_t =
common_reference_t<range_rvalue_reference_t<_Rs>...>;
+
+template <class... _Rs>
+concept __concat_indirectly_readable =
+ common_reference_with<__concat_reference_t<_Rs...>&&,
__concat_value_t<_Rs...>&> &&
+ common_reference_with<__concat_reference_t<_Rs...>&&,
__concat_rvalue_reference_t<_Rs...>&&> &&
+ common_reference_with<__concat_rvalue_reference_t<_Rs...>&&,
__concat_value_t<_Rs...> const&> &&
+ (__concat_indirectly_readable_impl<__concat_reference_t<_Rs...>,
+ __concat_rvalue_reference_t<_Rs...>,
+ iterator_t<_Rs>> &&
+ ...);
+
+template <class... _Rs>
+concept __concatable = requires {
+ typename __concat_reference_t<_Rs...>;
+ typename __concat_value_t<_Rs...>;
+ typename __concat_rvalue_reference_t<_Rs...>;
+} && __concat_indirectly_readable<_Rs...>;
+
+template <bool _Const, class... _Rs>
+concept __concat_is_random_access =
+ (random_access_range<__maybe_const<_Const, _Rs>> && ...) &&
(sized_range<__maybe_const<_Const, _Rs>> && ...);
+
+template <bool _Const, class... _Rs>
+concept __concat_is_bidirectional =
+ ((bidirectional_range<__maybe_const<_Const, _Rs>> && ...) &&
(common_range<__maybe_const<_Const, _Rs>> && ...));
+
+template <bool _Const, class... _Views>
+concept __all_forward = (forward_range<__maybe_const<_Const, _Views>> && ...);
+
+template <bool _Const, class... Ts>
+struct __apply_drop_first;
+
+template <bool _Const, class Head, class... Tail>
+struct __apply_drop_first<_Const, Head, Tail...> {
+ static constexpr bool value = (sized_range<__maybe_const<_Const, Tail>> &&
...);
+};
+
+template <input_range... _Views>
+ requires(view<_Views> && ...) && (sizeof...(_Views) > 0) &&
__concatable<_Views...>
+class concat_view : public view_interface<concat_view<_Views...>> {
+ tuple<_Views...> views_;
+
+ template <bool _Const>
+ class iterator;
+ class sentinel;
+
+public:
+ _LIBCPP_HIDE_FROM_ABI constexpr concat_view() = default;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr explicit concat_view(_Views... views) :
views_(std::move(views)...) {}
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator<false> begin()
+ requires(!(__simple_view<_Views> && ...))
+ {
+ iterator<false> it(this, in_place_index<0>, ranges::begin(get<0>(views_)));
+ it.template satisfy<0>();
+ return it;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator<true> begin() const
+ requires((range<const _Views> && ...) && __concatable<const _Views...>)
+ {
+ iterator<true> it(this, in_place_index<0>, ranges::begin(get<0>(views_)));
+ it.template satisfy<0>();
+ return it;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+ requires(!(__simple_view<_Views> && ...))
+ {
+ if constexpr (common_range<typename __last_view<_Views...>::type>) {
+ constexpr auto __N = sizeof...(_Views);
+ return iterator<false>(this, in_place_index<__N - 1>,
ranges::end(get<__N - 1>(views_)));
+ } else {
+ return default_sentinel;
+ }
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+ requires(range<const _Views> && ...)
+ {
+ if constexpr (common_range<typename __last_view<_Views...>::type>) {
+ constexpr auto __N = sizeof...(_Views);
+ return iterator<true>(this, in_place_index<__N - 1>, ranges::end(get<__N
- 1>(views_)));
+ } else {
+ return default_sentinel;
+ }
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+ requires(sized_range<_Views> && ...)
+ {
+ return apply(
+ [](auto... sizes) {
+ using CT = make_unsigned_t<common_type_t<decltype(sizes)...>>;
+ return (CT(sizes) + ...);
+ },
+ tuple_transform(ranges::size, views_));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+ requires(sized_range<const _Views> && ...)
+ {
+ return apply(
+ [](auto... sizes) {
+ using CT = make_unsigned_t<common_type_t<decltype(sizes)...>>;
+ return (CT(sizes) + ...);
+ },
+ tuple_transform(ranges::size, views_));
+ }
+};
+
+template <class... _Views>
+concat_view(_Views&&...) -> concat_view<views::all_t<_Views>...>;
+
+template <input_range... _Views>
+ requires(view<_Views> && ...) && (sizeof...(_Views) > 0) &&
__concatable<_Views...>
+template <bool _Const>
+class concat_view<_Views...>::iterator {
+public:
+ constexpr static bool derive_pack_random_iterator =
+ __derived_from_pack<typename
iterator_traits<iterator_t<__maybe_const<_Const,
_Views>>>::iterator_category...,
+ random_access_iterator_tag>::value;
+ constexpr static bool derive_pack_bidirectional_iterator =
+ __derived_from_pack<typename
iterator_traits<iterator_t<__maybe_const<_Const,
_Views>>>::iterator_category...,
+ bidirectional_iterator_tag>::value;
+ constexpr static bool derive_pack_forward_iterator =
+ __derived_from_pack<typename iterator_traits<
iterator_t<__maybe_const<_Const, _Views>>>::iterator_category...,
+ forward_iterator_tag>::value;
+ using iterator_category =
+ _If<!is_reference_v<__concat_reference_t<__maybe_const<_Const,
_Views>...>>,
+ input_iterator_tag,
+ _If<derive_pack_random_iterator,
+ random_access_iterator_tag,
+ _If<derive_pack_bidirectional_iterator,
+ bidirectional_iterator_tag,
+ _If<derive_pack_forward_iterator, forward_iterator_tag,
input_iterator_tag > > > >;
+ using iterator_concept =
+ _If<__concat_is_random_access<_Const, _Views...>,
+ random_access_iterator_tag,
+ _If<__concat_is_bidirectional<_Const, _Views...>,
+ bidirectional_iterator_tag,
+ _If< __all_forward<_Const, _Views...>, forward_iterator_tag,
input_iterator_tag > > >;
+ using value_type = __concat_value_t<__maybe_const<_Const, _Views>...>;
+ using difference_type =
common_type_t<range_difference_t<__maybe_const<_Const, _Views>>...>;
+ using base_iter = variant<iterator_t<__maybe_const<_Const,
_Views>>...>;
+
+ base_iter it_;
+ __maybe_const<_Const, concat_view>* parent_ = nullptr;
+
+ template <std::size_t N>
+ _LIBCPP_HIDE_FROM_ABI constexpr void satisfy() {
+ if constexpr (N < (sizeof...(_Views) - 1)) {
+ if (get<N>(it_) == ranges::end(get<N>(parent_->views_))) {
+ it_.template emplace<N + 1>(ranges::begin(get<N +
1>(parent_->views_)));
+ satisfy<N + 1>();
+ }
+ }
+ }
+
+ template <std::size_t N>
+ _LIBCPP_HIDE_FROM_ABI constexpr void prev() {
+ if constexpr (N == 0) {
+ --get<0>(it_);
+ } else {
+ if (get<N>(it_) == ranges::begin(get<N>(parent_->views_))) {
+ using prev_view = __maybe_const<_Const, tuple_element_t<N - 1,
tuple<_Views...>>>;
+ if constexpr (common_range<prev_view>) {
+ it_.emplace<N - 1>(ranges::end(get<N - 1>(parent_->views_)));
+ } else {
+ it_.emplace<N - 1>(
+ ranges::__next(ranges::begin(get<N - 1>(parent_->views_)),
ranges::size(get<N - 1>(parent_->views_))));
+ }
+ prev<N - 1>();
+ } else {
+ --get<N>(it_);
+ }
+ }
+ }
+
+ template <std::size_t N>
+ _LIBCPP_HIDE_FROM_ABI constexpr void advance_fwd(difference_type offset,
difference_type steps) {
+ using underlying_diff_type = iter_difference_t<variant_alternative_t<N,
base_iter>>;
+ if constexpr (N == sizeof...(_Views) - 1) {
+ get<N>(it_) += static_cast<underlying_diff_type>(steps);
+ } else {
+ difference_type n_size = ranges::size(get<N>(parent_->views_));
+ if (offset + steps < n_size) {
+ get<N>(it_) += static_cast<underlying_diff_type>(steps);
+ } else {
+ it_.template emplace<N + 1>(ranges::begin(get<N +
1>(parent_->views_)));
+ advance_fwd<N + 1>(0, offset + steps - n_size);
+ }
+ }
+ }
+
+ template <std::size_t N>
+ _LIBCPP_HIDE_FROM_ABI constexpr void advance_bwd(difference_type offset,
difference_type steps) {
+ using underlying_diff_type = iter_difference_t<variant_alternative_t<N,
base_iter>>;
+ if constexpr (N == 0) {
+ get<N>(it_) -= static_cast<underlying_diff_type>(steps);
+ } else {
+ if (offset >= steps) {
+ get<N>(it_) -= static_cast<underlying_diff_type>(steps);
+ } else {
+ auto prev_size = ranges::__distance(get<N - 1>(parent_->views_));
+ it_.emplace<N - 1>(ranges::begin(get<N - 1>(parent_->views_)) +
prev_size);
+ advance_bwd<N - 1>(prev_size, steps - offset);
+ }
+ }
+ }
+
+ template <size_t... Is, typename Func>
+ _LIBCPP_HIDE_FROM_ABI constexpr void
+ apply_fn_with_const_index(size_t index, Func&& func,
std::index_sequence<Is...>) {
+ ((index == Is ? (func(std::integral_constant<size_t, Is>{}), 0) : 0), ...);
+ }
+
+ template <size_t N, typename Func>
+ _LIBCPP_HIDE_FROM_ABI constexpr void apply_fn_with_const_index(size_t index,
Func&& func) {
+ apply_fn_with_const_index(index, std::forward<Func>(func),
std::make_index_sequence<N>{});
+ }
+
+ template <class... Args>
+ explicit constexpr iterator(__maybe_const<_Const, concat_view>* parent,
Args&&... args)
+ requires constructible_from<base_iter, Args&&...>
+ : it_(std::forward<Args>(args)...), parent_(parent) {}
+
+public:
+ _LIBCPP_HIDE_FROM_ABI iterator() = default;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator(iterator<!_Const> i)
+ requires _Const && (convertible_to<iterator_t<_Views>, iterator_t<const
_Views>> && ...)
+ : it_(base_iter(in_place_index<i.index()>,
std::get<i.index()>(std::move(i.it_)))), parent_(i.parent_) {}
+
+ _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const {
+ using reference = __concat_reference_t<__maybe_const<_Const, _Views>...>;
+ return std::visit([](auto&& it) -> reference { return *it; }, it_);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator& operator++() {
+ size_t active_index = it_.index();
+
apply_fn_with_const_index<std::variant_size_v<decltype(it_)>>(active_index,
[&](auto index_constant) {
+ constexpr size_t i = index_constant.value;
+ ++get<i>(it_);
+ satisfy<i>();
+ });
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr void operator++(int) { ++*this; }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator operator++(int)
+ requires(forward_range<__maybe_const<_Const, _Views>> && ...)
+ {
+ auto tmp = *this;
+ ++*this;
+ return tmp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator& operator--()
+ requires __concat_is_bidirectional<_Const, _Views...>
+ {
+ size_t active_index = it_.index();
+
apply_fn_with_const_index<std::variant_size_v<decltype(it_)>>(active_index,
[&](auto index_constant) {
+ constexpr size_t i = index_constant.value;
+ prev<i>();
+ });
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator operator--(int)
+ requires __concat_is_bidirectional<_Const, _Views...>
+ {
+ auto __tmp = *this;
+ --*this;
+ return __tmp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const iterator& x,
const iterator& y)
+ requires(equality_comparable<iterator_t<__maybe_const<_Const, _Views>>> &&
...)
+ {
+ return x.it_ == y.it_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator[](difference_type n)
const
+ requires __concat_is_random_access<_Const, _Views...>
+ {
+ return *((*this) + n);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr iterator operator+(const iterator&
it, difference_type n)
+ requires __concat_is_random_access<_Const, _Views...>
+ {
+ auto temp = it;
+ temp += n;
+ return temp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr iterator operator+(difference_type n,
const iterator& it)
+ requires __concat_is_random_access<_Const, _Views...>
+ {
+ return it + n;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator& operator+=(difference_type n)
+ requires __concat_is_random_access<_Const, _Views...>
+ {
+ size_t active_index = it_.index();
+ if (n > 0) {
+ std::visit(
+ [&](auto& active_it) {
+
apply_fn_with_const_index<std::tuple_size_v<decltype(parent_->views_)>>(
+ active_index, [&](auto index_constant) {
+ constexpr size_t I = index_constant.value;
+ auto& active_view = std::get<I>(parent_->views_);
+ difference_type idx = active_it - ranges::begin(active_view);
+ advance_fwd<I>(idx, n);
+ });
+ },
+ it_);
+ }
+
+ else if (n < 0) {
+ std::visit(
+ [&](auto& active_it) {
+
apply_fn_with_const_index<std::tuple_size_v<decltype(parent_->views_)>>(
+ active_index, [&](auto index_constant) {
+ constexpr size_t I = index_constant.value;
+ auto& active_view = std::get<I>(parent_->views_);
+ difference_type idx = active_it - ranges::begin(active_view);
+ advance_bwd<I>(idx, -n);
+ });
+ },
+ it_);
+ }
+
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr iterator& operator-=(difference_type n)
+ requires __concat_is_random_access<_Const, _Views...>
+ {
+ *this += -n;
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const iterator& it,
default_sentinel_t) {
+ constexpr auto last_idx = sizeof...(_Views) - 1;
+ return it.it_.index() == last_idx &&
+ std::get<last_idx>(it.it_) ==
ranges::end(std::get<last_idx>(it.parent_->views_));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<(const iterator& x,
const iterator& y)
+ requires(random_access_range<__maybe_const<_Const, _Views>> && ...)
+ {
+ return x.it_ < y.it_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>(const iterator& x,
const iterator& y)
+ requires(random_access_range<__maybe_const<_Const, _Views>> && ...)
+ {
+ return x.it_ > y.it_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator<=(const iterator& x,
const iterator& y)
+ requires(random_access_range<__maybe_const<_Const, _Views>> && ...)
+ {
+ return x.it_ <= y.it_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator>=(const iterator& x,
const iterator& y)
+ requires(random_access_range<__maybe_const<_Const, _Views>> && ...)
+ {
+ return x.it_ >= y.it_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr auto operator<=>(const iterator& x,
const iterator& y)
+ requires((random_access_range<__maybe_const<_Const, _Views>> && ...) &&
+ (three_way_comparable<__maybe_const<_Const, _Views>> && ...))
+ {
+ return x.it_ <=> y.it_;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr decltype(auto) iter_move(const
iterator& it) noexcept(
+
+ ((is_nothrow_invocable_v< decltype(ranges::iter_move), const
iterator_t<__maybe_const<_Const, _Views>>& >) &&
+ ...) &&
+ ((is_nothrow_convertible_v<
range_rvalue_reference_t<__maybe_const<_Const, _Views>>,
+
__concat_rvalue_reference_t<__maybe_const<_Const, _Views>...> >) &&
+ ...))
+
+ {
+ return std::visit(
+ [](const auto& i) -> __concat_rvalue_reference_t<__maybe_const<_Const,
_Views>...> {
+ return ranges::iter_move(i);
+ },
+ it.it_);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr void iter_swap(const iterator& x,
const iterator& y)
+
+ noexcept((noexcept(ranges::swap(*x, *y))) &&
+ (noexcept(ranges::iter_swap(std::declval<const
iterator_t<__maybe_const<_Const, _Views>>>(),
+ std::declval<const
iterator_t<__maybe_const<_Const, _Views>>>())) &&
+ ...))
+
+ requires swappable_with<iter_reference_t<iterator>,
iter_reference_t<iterator>> &&
+ (... && indirectly_swappable<iterator_t<__maybe_const<_Const,
_Views>>>)
+ {
+ std::visit(
+ [&](const auto& it1, const auto& it2) {
+ if constexpr (is_same_v<decltype(it1), decltype(it2)>) {
+ ranges::iter_swap(it1, it2);
+ } else {
+ ranges::swap(*x, *y);
+ }
+ },
+ x.it_,
+ y.it_);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const
iterator& x, const iterator& y)
+ requires __concat_is_random_access<_Const, _Views...>
+ {
+ size_t ix = x.it_.index();
+ size_t iy = y.it_.index();
+
+ if (ix > iy) {
+ std::visit(
+ [&](auto& it_x, auto& it_y) {
+
it_x.apply_fn_with_const_index<std::tuple_size_v<decltype(x.parent_->views_)>>(
+ ix, [&](auto index_constant) {
+ constexpr size_t index_x = index_constant.value;
+ auto dx =
ranges::__distance(ranges::begin(std::get<index_x>(x.parent_->views_)), it_x);
+
+
it_y.apply_fn_with_const_index<std::tuple_size_v<decltype(y.parent_->views_)>>(
+ iy, [&](auto index_constant) {
+ constexpr size_t index_y = index_constant.value;
+ auto dy =
ranges::__distance(ranges::begin(std::get<index_y>(y.parent_->views_)), it_y);
+ difference_type s = 0;
+ for (size_t idx = index_y + 1; idx < index_x; idx++) {
+ s += ranges::size(std::get<idx>(x.parent_->views_));
+ }
+ return dy + s + dx;
+ });
+ });
+ },
+ x.it_,
+ y.it_);
+ } else if (ix < iy) {
+ return -(y - x);
+ } else {
+ std::visit([&](const auto& it1, const auto& it2) { return it1 - it2; },
x.it_, y.it_);
+ }
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr iterator operator-(const iterator&
it, difference_type n)
+ requires __concat_is_random_access<_Const, _Views...>
+ {
+ auto temp = it;
+ temp -= n;
+ return temp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type operator-(const
iterator& x, default_sentinel_t)
+ requires(sized_sentinel_for<sentinel_t<__maybe_const<_Const, _Views>>,
iterator_t<__maybe_const<_Const, _Views>>> &&
+ ...) &&
+ (__apply_drop_first<_Const, _Views...>::value)
+ {
+ size_t ix = x.it_.index();
+ std::visit(
+ [&](auto& it_x) {
+
it_x.apply_fn_with_const_index<std::tuple_size_v<decltype(x.parent_->views_)>>(ix,
[&](auto index_constant) {
+ constexpr size_t index_x = index_constant.value;
+ auto dx =
ranges::__distance(ranges::begin(std::get<index_x>(x.parent_->views_)), it_x);
+
+ difference_type s = 0;
+ for (size_t idx = 0; idx < index_x; idx++) {
+ s += ranges::size(std::get<idx>(x.parent_->views_));
+ }
+
+ return -(dx + s);
+ });
+ },
+ x.it_);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type
operator-(default_sentinel_t, const iterator& x)
+ requires(sized_sentinel_for<sentinel_t<__maybe_const<_Const, _Views>>,
iterator_t<__maybe_const<_Const, _Views>>> &&
+ ...) &&
+ (__apply_drop_first<_Const, _Views...>::value)
+ {
+ -(x - default_sentinel);
+ }
+};
+
+namespace views {
+namespace __concat {
+struct __fn {
+ template <class... _Views>
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Views...
views) const
+ noexcept(concat_view(std::forward<_Views>(views)...)) ->
decltype(concat_view(std::forward<_Views>(views)...)) {
----------------
frederick-vs-ja wrote:
Missed `noexcept` operator.
```suggestion
noexcept(noexcept(concat_view(std::forward<_Views>(__views)...))) ->
decltype(concat_view(std::forward<_Views>(views)...)) {
```
https://github.com/llvm/llvm-project/pull/120920
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