[libcxx-commits] [libcxx] [libcxx] patch for implementing ranges::find_last (PR #67270)
via libcxx-commits
libcxx-commits at lists.llvm.org
Wed Jan 24 01:36:15 PST 2024
================
@@ -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>) {
+ // Optimized for common_range and bidirectional_range
+ _Ip __original_last = __last; // Save the original value of __last
+ while (__first != __last) {
+ --__last;
+ if (std::invoke(__pred, std::invoke(__proj, *__last))) {
+ return {__last, __original_last}; // Directly return the result
+ }
+ }
+ return {__last, __original_last};
+ } else if constexpr (bidirectional_iterator<_Ip> && assignable_from<_Ip&, _Sp&>) {
+ // For non-common but bidirectional ranges
+ _Ip __result = ranges::next(__first, __last);
+ _Ip __original_last = __result;
+ while (__first != __result) {
+ --__result;
+ if (std::invoke(__pred, std::invoke(__proj, *__result))) {
+ return {__result, __original_last};
+ }
+ }
+ return {__result, __original_last};
+ } else {
+ // Code for the non-bidirectional case
+ _Ip __original_first = __first;
+ _Ip __result = __first;
+ while (__first != __last) {
+ if (std::invoke(__pred, std::invoke(__proj, *__first))) {
+ __result = __first;
+ }
+ ++__first;
+ }
+ return {__result, __original_first};
----------------
huixie90 wrote:
The return value is not correct. you want to return the incremented iterator which equals to last
> Returns: Let i be the last iterator in the range [first, last) for which E is true[.](https://eel.is/c++draft/alg.find.last#2.sentence-1) Returns {i, last}, or {last, last} if no such iterator is found[.](https://eel.is/c++draft/alg.find.last#2.sentence-2)
Please add tests after the fix
https://github.com/llvm/llvm-project/pull/67270
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