================
@@ -0,0 +1,333 @@
+// -*- 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_ENUMERATE_VIEW_H
+#define _LIBCPP___RANGES_ENUMERATE_VIEW_H
+
+#include <__concepts/convertible_to.h>
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/distance.h>
+#include <__iterator/iter_move.h>
+#include <__iterator/iterator_traits.h>
+#include <__ranges/access.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/enable_borrowed_range.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/size.h>
+#include <__ranges/view_interface.h>
+#include <__type_traits/maybe_const.h>
+#include <__utility/forward.h>
+#include <__utility/move.h>
+#include <tuple>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+namespace ranges {
+
+// [concept.object]
+
+template <class _Rp>
+concept __range_with_movable_references =
+ ranges::input_range<_Rp> &&
std::move_constructible<ranges::range_reference_t<_Rp>> &&
+ std::move_constructible<ranges::range_rvalue_reference_t<_Rp>>;
+
+// [range.enumerate.view]
+
+template <view _View>
+ requires __range_with_movable_references<_View>
+class enumerate_view : public view_interface<enumerate_view<_View>> {
+ _View __base_ = _View();
+
+ // [range.enumerate.iterator]
+ template <bool _Const>
+ class __iterator;
+
+ // [range.enumerate.sentinel]
+ template <bool _Const>
+ class __sentinel;
+
+ template <bool _AnyConst>
+ _LIBCPP_HIDE_FROM_ABI static constexpr decltype(auto) __get_current(const
__iterator<_AnyConst>& __iter) {
+ return (__iter.__current_);
+ }
+
+public:
+ _LIBCPP_HIDE_FROM_ABI constexpr enumerate_view()
+ requires(default_initializable<_View>)
+ = default;
+ _LIBCPP_HIDE_FROM_ABI constexpr explicit enumerate_view(_View __base) :
__base_(std::move(__base)){};
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
+ requires(!__simple_view<_View>)
+ {
+ return __iterator<false>(ranges::begin(__base_), 0);
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+ requires __range_with_movable_references<const _View>
+ {
+ return __iterator<true>(ranges::begin(__base_), 0);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+ requires(!__simple_view<_View>)
+ {
+ if constexpr (common_range<_View> && sized_range<_View>)
+ return __iterator<false>(ranges::end(__base_),
ranges::distance(__base_));
+ else
+ return __sentinel<false>(ranges::end(__base_));
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+ requires __range_with_movable_references<const _View>
+ {
+ if constexpr (common_range<const _View> && sized_range<const _View>)
+ return __iterator<true>(ranges::end(__base_), ranges::distance(__base_));
+ else
+ return __sentinel<true>(ranges::end(__base_));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+ requires sized_range<_View>
+ {
+ return ranges::size(__base_);
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+ requires sized_range<const _View>
+ {
+ return ranges::size(__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_);
}
+};
+
+template <class _Range>
+enumerate_view(_Range&&) -> enumerate_view<views::all_t<_Range>>;
+
+// [range.enumerate.iterator]
+
+template <view _View>
+ requires __range_with_movable_references<_View>
+template <bool _Const>
+class enumerate_view<_View>::__iterator {
+ using _Base = __maybe_const<_Const, _View>;
+
+ static consteval auto __get_iterator_concept() {
+ if constexpr (random_access_range<_Base>) {
+ return random_access_iterator_tag{};
+ } else if constexpr (bidirectional_range<_Base>) {
+ return bidirectional_iterator_tag{};
+ } else if constexpr (forward_range<_Base>) {
+ return forward_iterator_tag{};
+ } else {
+ return input_iterator_tag{};
+ }
+ }
+
+ friend class enumerate_view<_View>;
+
+public:
+ using iterator_category = input_iterator_tag;
+ using iterator_concept = decltype(__get_iterator_concept());
+ using difference_type = range_difference_t<_Base>;
+ using value_type = tuple<difference_type, range_value_t<_Base>>;
+
+private:
+ using __reference_type = tuple<difference_type,
range_reference_t<_Base>>;
+ iterator_t<_Base> __current_ = iterator_t<_Base>();
+ difference_type __pos_ = 0;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr explicit __iterator(iterator_t<_Base>
__current, difference_type __pos)
+ : __current_(std::move(__current)), __pos_(__pos) {}
+
+public:
+ _LIBCPP_HIDE_FROM_ABI __iterator()
+ requires(default_initializable<iterator_t<_Base>>)
----------------
cjdb wrote:
```suggestion
requires default_initializable<iterator_t<_Base>>
```
https://github.com/llvm/llvm-project/pull/73617
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