[libcxx-commits] [libcxx] [libcxx] patch for implementing ranges::find_last (PR #67270)

[via libcxx-commits]

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@@ -0,0 +1,104 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___ALGORITHM_RANGES_FIND_LAST_IF_H
+#define _LIBCPP___ALGORITHM_RANGES_FIND_LAST_IF_H
+
+#include <__concepts/assignable.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__iterator/concepts.h>
+#include <__iterator/next.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/subrange.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER >= 23
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+template <class _Ip, class _Sp, class _Pred, class _Proj>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI static constexpr subrange<_Ip>
+__find_last_if_impl(_Ip __first, _Sp __last, _Pred&& __pred, _Proj&& __proj) {
+  if constexpr (common_range<_Ip> && bidirectional_range<_Ip>) {
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huixie90 wrote:

This is incorrect. since here you passed in iterator and sentinel, not the range itself, so they will never be `common_range` or `bidirectional_range`. I think your second branch almost covers it except that instead of directly copying the last, it copies the first then assigns it to the last. If we want to keep this branch, I think the correct check is to check iterator and sentinel are the same type and the iterator models bidi iterator

https://github.com/llvm/llvm-project/pull/67270