From 0d94c6df183375caaa7f672e288a2094ca813749 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Fri, 14 Apr 2023 10:32:12 -0400
Subject: libstdc++: Implement P2278R4 "cbegin should always return a constant
 iterator"

This also implements the approved follow-up LWG issues 3765, 3766, 3769,
3770, 3811, 3850, 3853, 3862 and 3872.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_base.h (const_iterator_t): Define for C++23.
	(const_sentinel_t): Likewise.
	(range_const_reference_t): Likewise.
	(constant_range): Likewise.
	(__cust_access::__possibly_const_range): Likewise, replacing ...
	(__cust_access::__as_const): ... this.
	(__cust_access::_CBegin::operator()): Redefine for C++23 as per P2278R4.
	(__cust_access::_CEnd::operator()): Likewise.
	(__cust_access::_CRBegin::operator()): Likewise.
	(__cust_access::_CREnd::operator()): Likewise.
	(__cust_access::_CData::operator()): Likewise.
	* include/bits/ranges_util.h (ranges::__detail::__different_from):
	Make it an alias of std::__detail::__different_from.
	(view_interface::cbegin): Define for C++23.
	(view_interface::cend): Likewise.
	* include/bits/stl_iterator.h (__detail::__different_from): Define.
	(iter_const_reference_t): Define for C++23.
	(__detail::__constant_iterator): Likewise.
	(__detail::__is_const_iterator): Likewise.
	(__detail::__not_a_const_iterator): Likewise.
	(__detail::__iter_const_rvalue_reference_t): Likewise.
	(__detail::__basic_const_iter_cat):: Likewise.
	(const_iterator): Likewise.
	(__detail::__const_sentinel): Likewise.
	(const_sentinel): Likewise.
	(basic_const_iterator): Likewise.
	(common_type<basic_const_iterator<_Tp>, _Up>): Likewise.
	(common_type<_Up, basic_const_iterator<_Tp>>): Likewise.
	(common_type<basic_const_iterator<_Tp>, basic_const_iterator<Up>>):
	Likewise.
	(make_const_iterator): Define for C++23.
	(make_const_sentinel): Likewise.
	* include/std/ranges (__cpp_lib_ranges_as_const): Likewise.
	(as_const_view): Likewise.
	(enable_borrowed_range<as_const_view>): Likewise.
	(views::__detail::__is_ref_view): Likewise.
	(views::__detail::__can_is_const_view): Likewise.
	(views::_AsConst, views::as_const): Likewise.
	* include/std/span (span::const_iterator): Likewise.
	(span::const_reverse_iterator): Likewise.
	(span::cbegin): Likewise.
	(span::cend): Likewise.
	(span::crbegin): Likewise.
	(span::crend): Likewise.
	* include/std/version (__cpp_lib_ranges_as_const): Likewise.
	* testsuite/std/ranges/adaptors/join.cc (test06): Adjust to
	behave independently of C++20 vs C++23.
	* testsuite/std/ranges/version_c++23.cc: Verify value of
	__cpp_lib_ranges_as_const macro.
	* testsuite/24_iterators/const_iterator/1.cc: New test.
	* testsuite/std/ranges/adaptors/as_const/1.cc: New test.
---
 libstdc++-v3/include/std/version | 1 +
 1 file changed, 1 insertion(+)

(limited to 'libstdc++-v3/include/std/version')

diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index d233b03..9f31f25 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -339,6 +339,7 @@
 #define __cpp_lib_ranges_stride 202207L
 #define __cpp_lib_ranges_cartesian_product 202207L
 #define __cpp_lib_ranges_as_rvalue 202207L
+#define __cpp_lib_ranges_as_const 202207L
 #define __cpp_lib_ranges_enumerate 202302L
 #define __cpp_lib_fold 202207L
 #if __cpp_constexpr_dynamic_alloc
-- 
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