[libcxx-commits] [libcxx] [libc++] The rest of P2278R4 (cdata, as_const_view, span changes) (PR #102301)

[A. Jiang via libcxx-commits]

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@@ -0,0 +1,250 @@
+// -*- 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_CONST_ACCESS_H
+#define _LIBCPP___RANGES_CONST_ACCESS_H
+
+#include <__iterator/const_iterator.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/enable_borrowed_range.h>
+#include <__ranges/rbegin.h>
+#include <__ranges/rend.h>
+#include <__type_traits/is_reference.h>
+#include <__type_traits/remove_cv.h>
+#include <__type_traits/remove_reference.h>
+#include <__utility/declval.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// [range.const]
+#  if _LIBCPP_STD_VER >= 23
+namespace ranges {
+template <input_range _Rp>
+constexpr auto& __possibly_const_range(_Rp& __rng) noexcept {
+  if constexpr (constant_range<const _Rp> && !constant_range<_Rp>) {
+    return const_cast<const _Rp&>(__rng);
+  } else {
+    return __rng;
+  }
+}
+} // namespace ranges
+#  endif // _LIBCPP_STD_VER >= 23
+
+// [range.access.cbegin]
+namespace ranges {
+
+template <class _Type>
+concept __const_accessible_range = (!is_rvalue_reference_v<_Type&&> || enable_borrowed_range<remove_cv_t<_Type>>);
+
+namespace __cbegin {
+struct __fn {
+#  if _LIBCPP_STD_VER >= 23
+  template <class _Rng>
+  using _UType = decltype(ranges::begin(ranges::__possibly_const_range(std::declval<_Rng&>())));
+
+  template <__const_accessible_range _Rng>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static auto
+  operator()(_Rng&& __rng) noexcept(noexcept(const_iterator<_UType<_Rng>>(
+      ranges::begin(ranges::__possibly_const_range(__rng))))) -> const_iterator<_UType<_Rng>> {
+    return const_iterator<_UType<_Rng>>(ranges::begin(ranges::__possibly_const_range(__rng)));
+  }
+#  else  // ^^^ _LIBCPP_STD_VER >= 23 / _LIBCPP_STD_VER < 23 vvv
+  template <class _Tp>
+    requires is_lvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(ranges::begin(static_cast<const remove_reference_t<_Tp>&>(__t))))
+          -> decltype(ranges::begin(static_cast<const remove_reference_t<_Tp>&>(__t))) {
+    return ranges::begin(static_cast<const remove_reference_t<_Tp>&>(__t));
+  }
+
+  template <class _Tp>
+    requires is_rvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(ranges::begin(static_cast<const _Tp&&>(__t))))
+          -> decltype(ranges::begin(static_cast<const _Tp&&>(__t))) {
+    return ranges::begin(static_cast<const _Tp&&>(__t));
+  }
+#  endif // ^^^ _LIBCPP_STD_VER < 23
+};
+} // namespace __cbegin
+
+inline namespace __cpo {
+inline constexpr auto cbegin = __cbegin::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+// [range.access.cend]
+namespace ranges {
+namespace __cend {
+struct __fn {
+#  if _LIBCPP_STD_VER >= 23
+  template <class _Rng>
+  using _UType = decltype(ranges::end(ranges::__possibly_const_range(std::declval<_Rng&>())));
+
+  template <__const_accessible_range _Rng>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static auto
+  operator()(_Rng&& __rng) noexcept(noexcept(const_sentinel<_UType<_Rng>>(
+      ranges::end(ranges::__possibly_const_range(__rng))))) -> const_sentinel<_UType<_Rng>> {
+    return const_sentinel<_UType<_Rng>>(ranges::end(ranges::__possibly_const_range(__rng)));
+  }
+#  else // ^^^ _LIBCPP_STD_VER >= 23 / _LIBCPP_STD_VER < 23 vvv
+  template <class _Tp>
+    requires is_lvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(ranges::end(static_cast<const remove_reference_t<_Tp>&>(__t))))
+          -> decltype(ranges::end(static_cast<const remove_reference_t<_Tp>&>(__t))) {
+    return ranges::end(static_cast<const remove_reference_t<_Tp>&>(__t));
+  }
+
+  template <class _Tp>
+    requires is_rvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const noexcept(
+      noexcept(ranges::end(static_cast<const _Tp&&>(__t)))) -> decltype(ranges::end(static_cast<const _Tp&&>(__t))) {
+    return ranges::end(static_cast<const _Tp&&>(__t));
+  }
+#  endif
+};
+} // namespace __cend
+
+inline namespace __cpo {
+inline constexpr auto cend = __cend::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+// [range.access.crbegin]
+namespace ranges {
+namespace __crbegin {
+struct __fn {
+#  if _LIBCPP_STD_VER >= 23
+  template <class _Rng>
+  using _UType = decltype(ranges::rbegin(ranges::__possibly_const_range(std::declval<_Rng&>())));
+
+  template <__const_accessible_range _Rng>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static auto
+  operator()(_Rng&& __rng) noexcept(noexcept(const_iterator<_UType<_Rng>>(
+      ranges::rbegin(ranges::__possibly_const_range(__rng))))) -> const_iterator<_UType<_Rng>> {
+    return const_iterator<_UType<_Rng>>(ranges::rbegin(ranges::__possibly_const_range(__rng)));
+  }
+#  else  // ^^^ _LIBCPP_STD_VER >= 23 / _LIBCPP_STD_VER < 23
+  template <class _Tp>
+    requires is_lvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(ranges::rbegin(static_cast<const remove_reference_t<_Tp>&>(__t))))
+          -> decltype(ranges::rbegin(static_cast<const remove_reference_t<_Tp>&>(__t))) {
+    return ranges::rbegin(static_cast<const remove_reference_t<_Tp>&>(__t));
+  }
+
+  template <class _Tp>
+    requires is_rvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(ranges::rbegin(static_cast<const _Tp&&>(__t))))
+          -> decltype(ranges::rbegin(static_cast<const _Tp&&>(__t))) {
+    return ranges::rbegin(static_cast<const _Tp&&>(__t));
+  }
+#  endif // ^^^ _LIBCPP_STD_VER < 23
+};
+} // namespace __crbegin
+
+inline namespace __cpo {
+inline constexpr auto crbegin = __crbegin::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+// [range.access.crend]
+namespace ranges {
+namespace __crend {
+struct __fn {
+#  if _LIBCPP_STD_VER >= 23
+  template <class _Rng>
+  using _UType = decltype(ranges::rend(ranges::__possibly_const_range(std::declval<_Rng&>())));
+
+  template <__const_accessible_range _Rng>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr static auto
+  operator()(_Rng&& __rng) noexcept(noexcept(const_sentinel<_UType<_Rng>>(
+      ranges::rend(ranges::__possibly_const_range(__rng))))) -> const_sentinel<_UType<_Rng>> {
+    return const_sentinel<_UType<_Rng>>(ranges::rend(ranges::__possibly_const_range(__rng)));
+  }
+#  else  // ^^^ _LIBCPP_STD_VER >= 23 / _LIBCPP_STD_VER < 23 vvv
+  template <class _Tp>
+    requires is_lvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const
+      noexcept(noexcept(ranges::rend(static_cast<const remove_reference_t<_Tp>&>(__t))))
+          -> decltype(ranges::rend(static_cast<const remove_reference_t<_Tp>&>(__t))) {
+    return ranges::rend(static_cast<const remove_reference_t<_Tp>&>(__t));
+  }
+
+  template <class _Tp>
+    requires is_rvalue_reference_v<_Tp&&>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t) const noexcept(
+      noexcept(ranges::rend(static_cast<const _Tp&&>(__t)))) -> decltype(ranges::rend(static_cast<const _Tp&&>(__t))) {
+    return ranges::rend(static_cast<const _Tp&&>(__t));
+  }
+#  endif // ^^^ _LIBCPP_STD_VER < 23
+};
+} // namespace __crend
+
+inline namespace __cpo {
+inline constexpr auto crend = __crend::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+// [range.prim.cdata]
+
+namespace ranges {
+namespace __cdata {
+struct __fn {
+#  if _LIBCPP_STD_VER >= 23
+  template <class _Tp>
+  _LIBCPP_HIDE_FROM_ABI constexpr static auto __as_const_pointer(const _Tp* __ptr) noexcept {
----------------
frederick-vs-ja wrote:

Ditto for [LWG3948](https://cplusplus.github.io/LWG/issue3948) (assuming the #99915 will be merged first):
https://github.com/llvm/llvm-project/blob/445023f1739d3764f1dae6e6b7b0602328198a1e/libcxx/docs/Status/Cxx2cIssues.csv#L30

https://github.com/llvm/llvm-project/pull/102301