[libcxx-commits] [libcxx] a3f8480 - [libcxx] Modify `std::__for_each{, _n}` to accept r-values in `__f` (#179451)

[via libcxx-commits]

Author: Connector Switch
Date: 2026-02-04T23:15:21+08:00
New Revision: a3f848057be438a570655ee3ca48a1178e898658

URL: https://github.com/llvm/llvm-project/commit/a3f848057be438a570655ee3ca48a1178e898658
DIFF: https://github.com/llvm/llvm-project/commit/a3f848057be438a570655ee3ca48a1178e898658.diff

LOG: [libcxx] Modify `std::__for_each{, _n}` to accept r-values in `__f` (#179451)

This is necessary when optimizing algorithms for segmented iterators to
reduce boilerplate code.

related:
-
https://github.com/llvm/llvm-project/pull/177853#discussion_r2754820322
-
https://github.com/llvm/llvm-project/pull/164266#discussion_r2447129525

Added: 
    

Modified: 
    libcxx/include/__algorithm/for_each.h
    libcxx/include/__algorithm/for_each_n.h
    libcxx/include/__algorithm/generate_n.h

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__algorithm/for_each.h b/libcxx/include/__algorithm/for_each.h
index 85fedce3d936d..bb656a2db0188 100644
--- a/libcxx/include/__algorithm/for_each.h
+++ b/libcxx/include/__algorithm/for_each.h
@@ -26,7 +26,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Sent, class _Func, class _Proj>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
-__for_each(_InputIterator __first, _Sent __last, _Func& __func, _Proj& __proj) {
+__for_each(_InputIterator __first, _Sent __last, _Func&& __func, _Proj& __proj) {
 #ifndef _LIBCPP_CXX03_LANG
   if constexpr (using _SpecialAlg =
                     __specialized_algorithm<_Algorithm::__for_each, __iterator_pair<_InputIterator, _Sent>>;

diff  --git a/libcxx/include/__algorithm/for_each_n.h b/libcxx/include/__algorithm/for_each_n.h
index 72c7adb093f95..7ff3f9b157c02 100644
--- a/libcxx/include/__algorithm/for_each_n.h
+++ b/libcxx/include/__algorithm/for_each_n.h
@@ -18,6 +18,7 @@
 #include <__iterator/segmented_iterator.h>
 #include <__type_traits/invoke.h>
 #include <__utility/convert_to_integral.h>
+#include <__utility/forward.h>
 #include <__utility/move.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -31,7 +32,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Size, class _Func, class _Proj>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
-__for_each_n(_InputIterator __first, _Size __orig_n, _Func& __f, _Proj& __proj) {
+__for_each_n(_InputIterator __first, _Size __orig_n, _Func&& __f, _Proj& __proj) {
   typedef decltype(std::__convert_to_integral(__orig_n)) _IntegralSize;
   _IntegralSize __n = __orig_n;
 
@@ -43,7 +44,7 @@ __for_each_n(_InputIterator __first, _Size __orig_n, _Func& __f, _Proj& __proj)
         std::__for_each(__lfirst, __llast, __f, __proj);
       });
     } else {
-      return std::__for_each(__first, __first + __n, __f, __proj);
+      return std::__for_each(__first, __first + __n, std::forward<_Func>(__f), __proj);
     }
   } else
 #endif

diff  --git a/libcxx/include/__algorithm/generate_n.h b/libcxx/include/__algorithm/generate_n.h
index 23899e49e0b65..ba04eb62e3c3a 100644
--- a/libcxx/include/__algorithm/generate_n.h
+++ b/libcxx/include/__algorithm/generate_n.h
@@ -29,8 +29,11 @@ inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator
 __generate_n(_OutputIterator __first, _Size __orig_n, _Generator& __gen) {
   using __iter_ref = decltype(*__first);
   __identity __proj;
-  auto __f = [&](__iter_ref __element) { std::forward<__iter_ref>(__element) = __gen(); };
-  return std::__for_each_n(std::move(__first), __orig_n, __f, __proj);
+  return std::__for_each_n(
+      std::move(__first),
+      __orig_n,
+      [&](__iter_ref __element) { std::forward<__iter_ref>(__element) = __gen(); },
+      __proj);
 }
 
 template <class _OutputIterator, class _Size, class _Generator>