[libcxx-commits] [libcxx] [libc++] Optimize std::for_each_n for segmented iterators (PR #135468)

[Louis Dionne via libcxx-commits]

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@@ -10,32 +10,88 @@
 #ifndef _LIBCPP___ALGORITHM_FOR_EACH_N_H
 #define _LIBCPP___ALGORITHM_FOR_EACH_N_H
 
+#include <__algorithm/for_each.h>
+#include <__algorithm/for_each_n_segment.h>
 #include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/segmented_iterator.h>
+#include <__type_traits/enable_if.h>
 #include <__utility/convert_to_integral.h>
+#include <__utility/move.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
-_LIBCPP_BEGIN_NAMESPACE_STD
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
 
-#if _LIBCPP_STD_VER >= 17
+_LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _InputIterator, class _Size, class _Function>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
-for_each_n(_InputIterator __first, _Size __orig_n, _Function __f) {
+template <class _InputIterator,
+          class _Size,
+          class _Func,
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ldionne wrote:

It would also be nice to add a test that fails if the TODO is not addressed. That would basically require passing a non random access segmented iterator that does NOT have a random access local iterator. Without the TODO addressed, `std::for_each_n` should fail to instantiate.

An example of that would be `join_view<list<char>>`. Can you validate that it indeed fails before you address the TODO?

https://github.com/llvm/llvm-project/pull/135468