[libcxx-commits] [libcxx] [libcxx] P2278R4: implement `{basic_, }const_iterator`, and have `cbegin` et. al. return it (PR #99915)
A. Jiang via libcxx-commits
libcxx-commits at lists.llvm.org
Wed Aug 7 10:23:17 PDT 2024
================
@@ -0,0 +1,351 @@
+// -*- 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___ITERATOR_CONST_ITERATOR_H
+#define _LIBCPP___ITERATOR_CONST_ITERATOR_H
+
+#include <__compare/three_way_comparable.h>
+#include <__concepts/common_with.h>
+#include <__concepts/convertible_to.h>
+#include <__concepts/different_from.h>
+#include <__concepts/same_as.h>
+#include <__concepts/semiregular.h>
+#include <__concepts/totally_ordered.h>
+#include <__iterator/concepts.h>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/iter_move.h>
+#include <__iterator/iterator_traits.h>
+#include <__memory/addressof.h>
+#include <__memory/pointer_traits.h>
+#include <__type_traits/common_reference.h>
+#include <__type_traits/common_type.h>
+#include <__type_traits/conditional.h>
+#include <__type_traits/integral_constant.h>
+#include <__type_traits/is_reference.h>
+#include <__type_traits/is_specialization.h>
+#include <__utility/forward.h>
+#include <__utility/move.h>
+
+#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
+
+template <indirectly_readable _Iter>
+using iter_const_reference_t = common_reference_t<const iter_value_t<_Iter>&&, iter_reference_t<_Iter>>;
+
+template <class _Iter>
+concept __constant_iterator = input_iterator<_Iter> && same_as<iter_const_reference_t<_Iter>, iter_reference_t<_Iter>>;
+
+template <input_iterator _Iter>
+class basic_const_iterator;
+
+template <input_iterator _Iter>
+using const_iterator = conditional_t<__constant_iterator<_Iter>, _Iter, basic_const_iterator<_Iter>>;
+
+// This doesn't use `conditional_t` to avoid instantiating const_iterator<_Sent> when _Sent is not an input_iterator.
+template <class _Sent>
+struct __const_sentinel_impl {
+ using type = _Sent;
+};
+template <class _Sent>
+ requires input_iterator<_Sent>
+struct __const_sentinel_impl<_Sent> {
+ using type = const_iterator<_Sent>;
+};
+template <semiregular _Sent>
+using const_sentinel = __const_sentinel_impl<_Sent>::type;
+
+template <class _Iter>
+concept __not_a_const_iterator = !__is_specialization_v<_Iter, basic_const_iterator>;
+
+template <indirectly_readable _Iter>
+using __iter_const_rvalue_reference_t = common_reference_t<const iter_value_t<_Iter>&&, iter_rvalue_reference_t<_Iter>>;
+
+template <class _Iter>
+struct __basic_const_iterator_concept {
+ // clang-format off
+ using iterator_concept =
+ conditional_t<contiguous_iterator<_Iter>,
+ contiguous_iterator_tag,
+ conditional_t<random_access_iterator<_Iter>,
+ random_access_iterator_tag,
+ conditional_t<bidirectional_iterator<_Iter>,
+ bidirectional_iterator_tag,
+ conditional_t<forward_iterator<_Iter>,
+ forward_iterator_tag,
+ // else
+ input_iterator_tag>>>>;
+ // clang-format on
+};
+
+template <class _Iter>
+struct __basic_const_iterator_category : __basic_const_iterator_concept<_Iter> {};
+template <forward_iterator _Iter>
+struct __basic_const_iterator_category<_Iter> : __basic_const_iterator_concept<_Iter> {
+ using iterator_category = std::iterator_traits<_Iter>::iterator_category;
+};
+
+template <input_iterator _Iter>
+class _LIBCPP_TEMPLATE_VIS basic_const_iterator : public __basic_const_iterator_category<_Iter> {
+ _Iter __current = _Iter();
+
+ using __reference = iter_const_reference_t<_Iter>;
+ using __rvalue_reference = __iter_const_rvalue_reference_t<_Iter>;
+
+public:
+ using value_type = iter_value_t<_Iter>;
+ using difference_type = iter_difference_t<_Iter>;
+
+ _LIBCPP_HIDE_FROM_ABI basic_const_iterator()
+ requires default_initializable<_Iter>
+ = default;
+
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator(_Iter __cur) : __current(std::move(__cur)) {}
+ template <convertible_to<_Iter> _Type>
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator(basic_const_iterator<_Type> __cur)
+ : __current(std::move(__cur.__current)) {}
+ template <__different_from<basic_const_iterator> _Type>
+ requires convertible_to<_Type, _Iter>
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator(_Type&& __cur) : __current(std::forward<_Type>(__cur)) {}
+
+ _LIBCPP_HIDE_FROM_ABI constexpr const _Iter& base() const& noexcept { return __current; }
+ _LIBCPP_HIDE_FROM_ABI constexpr _Iter base() && { return std::move(__current); }
+
+ constexpr __reference operator*() const { return static_cast<__reference>(*__current); }
+ _LIBCPP_HIDE_FROM_ABI constexpr const auto* operator->() const
+ requires is_lvalue_reference_v<iter_reference_t<_Iter>> &&
+ same_as<remove_cvref_t<iter_reference_t<_Iter>>, value_type>
+ {
+ if constexpr (contiguous_iterator<_Iter>) {
+ return std::to_address(__current);
+ } else {
+ return std::addressof(*__current);
+ }
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator& operator++() {
+ ++__current;
+ return *this;
+ }
+ constexpr void operator++(int) { ++__current; }
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator operator++(int)
+ requires forward_iterator<_Iter>
+ {
+ auto __tmp = *this;
+ ++__current;
+ return __tmp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator& operator--()
+ requires bidirectional_iterator<_Iter>
+ {
+ --__current;
+ return *this;
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator operator--(int)
+ requires bidirectional_iterator<_Iter>
+ {
+ auto __tmp = *this;
+ --__current;
+ return __tmp;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator& operator+=(difference_type __n)
+ requires random_access_iterator<_Iter>
+ {
+ __current += __n;
+ return *this;
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator& operator-=(difference_type __n)
+ requires random_access_iterator<_Iter>
+ {
+ __current -= __n;
+ return *this;
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr __reference operator[](difference_type __n) const
+ requires random_access_iterator<_Iter>
+ {
+ return static_cast<__reference>(__current[__n]);
+ }
+
+ template <sentinel_for<_Iter> _Sent>
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const _Sent& __sent) const {
+ return __current == __sent;
+ }
+
+ template <__not_a_const_iterator _ConstIt>
+ requires __constant_iterator<_ConstIt> && convertible_to<_Iter const&, _ConstIt>
+ _LIBCPP_HIDE_FROM_ABI constexpr operator _ConstIt() const& {
+ return __current;
+ }
+ template <__not_a_const_iterator _ConstIt>
+ requires __constant_iterator<_ConstIt> && convertible_to<_Iter, _ConstIt>
+ _LIBCPP_HIDE_FROM_ABI constexpr operator _ConstIt() && {
+ return std::move(__current);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const basic_const_iterator& __rhs) const
+ requires random_access_iterator<_Iter>
+ {
+ return __current < __rhs.__current;
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const basic_const_iterator& __rhs) const
+ requires random_access_iterator<_Iter>
+ {
+ return __current > __rhs.__current;
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const basic_const_iterator& __rhs) const
+ requires random_access_iterator<_Iter>
+ {
+ return __current <= __rhs.__current;
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const basic_const_iterator& __rhs) const
+ requires random_access_iterator<_Iter>
+ {
+ return __current >= __rhs.__current;
+ }
+ _LIBCPP_HIDE_FROM_ABI constexpr auto operator<=>(const basic_const_iterator& __rhs) const
+ requires random_access_iterator<_Iter> && three_way_comparable<_Iter>
+ {
+ return __current <=> __rhs.__current;
+ }
+
+ template <__different_from<basic_const_iterator> _Iter2>
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const _Iter2& __rhs) const
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __current < __rhs;
+ }
+ template <__different_from<basic_const_iterator> _Iter2>
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const _Iter2& __rhs) const
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __current > __rhs;
+ }
+ template <__different_from<basic_const_iterator> _Iter2>
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const _Iter2& __rhs) const
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __current <= __rhs;
+ }
+ template <__different_from<basic_const_iterator> _Iter2>
+ _LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const _Iter2& __rhs) const
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __current >= __rhs;
+ }
+ template <__different_from<basic_const_iterator> _Iter2>
+ _LIBCPP_HIDE_FROM_ABI constexpr auto operator<=>(const _Iter2& __rhs) const
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2> &&
+ three_way_comparable_with<_Iter, _Iter2>
+ {
+ return __current <=> __rhs;
+ }
+
+ template <__not_a_const_iterator _Iter2>
+ friend _LIBCPP_HIDE_FROM_ABI constexpr bool operator<(const _Iter2& __lhs, const basic_const_iterator& __rhs)
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __lhs < __rhs.__current;
+ }
+ template <__not_a_const_iterator _Iter2>
+ friend _LIBCPP_HIDE_FROM_ABI constexpr bool operator>(const _Iter2& __lhs, const basic_const_iterator& __rhs)
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __lhs > __rhs.__current;
+ }
+ template <__not_a_const_iterator _Iter2>
+ friend _LIBCPP_HIDE_FROM_ABI constexpr bool operator<=(const _Iter2& __lhs, const basic_const_iterator& __rhs)
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __lhs <= __rhs.__current;
+ }
+ template <__not_a_const_iterator _Iter2>
+ friend _LIBCPP_HIDE_FROM_ABI constexpr bool operator>=(const _Iter2& __lhs, const basic_const_iterator& __rhs)
+ requires random_access_iterator<_Iter> && totally_ordered_with<_Iter, _Iter2>
+ {
+ return __lhs >= __rhs.__current;
+ }
+
+ friend _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator
+ operator+(const basic_const_iterator& __it, difference_type __n)
+ requires random_access_iterator<_Iter>
+ {
+ return basic_const_iterator(__it.__current + __n);
+ }
+ friend _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator
+ operator+(difference_type __n, const basic_const_iterator& __it)
+ requires random_access_iterator<_Iter>
+ {
+ return basic_const_iterator(__it.__current + __n);
+ }
+
+ friend _LIBCPP_HIDE_FROM_ABI constexpr basic_const_iterator
+ operator-(const basic_const_iterator& __it, difference_type __n)
+ requires random_access_iterator<_Iter>
+ {
+ return basic_const_iterator(__it.__current - __n);
+ }
+ template <sized_sentinel_for<_Iter> _Sent>
+ _LIBCPP_HIDE_FROM_ABI constexpr difference_type operator-(const _Sent& __rhs) const {
+ return __current - __rhs;
+ }
+ template <__not_a_const_iterator _Sent>
+ requires sized_sentinel_for<_Sent, _Iter>
+ friend _LIBCPP_HIDE_FROM_ABI constexpr difference_type
+ operator-(const _Sent& __lhs, const basic_const_iterator& __rhs) {
+ return __lhs - __rhs;
+ }
+
+ friend _LIBCPP_HIDE_FROM_ABI constexpr __rvalue_reference iter_move(const basic_const_iterator& __it) noexcept(
+ noexcept(static_cast<__rvalue_reference>(ranges::iter_move(__it.__current)))) {
+ return static_cast<__rvalue_reference>(ranges::iter_move(__it.__current));
+ }
+};
+
+template <class _Type1, common_with<_Type1> _Type2>
+ requires input_iterator<common_type_t<_Type1, _Type2>>
----------------
frederick-vs-ja wrote:
Ditto for [LWG3862](https://cplusplus.github.io/LWG/issue3862):
https://github.com/llvm/llvm-project/blob/445023f1739d3764f1dae6e6b7b0602328198a1e/libcxx/docs/Status/Cxx23Issues.csv#L296
https://github.com/llvm/llvm-project/pull/99915
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