use std::forward

Author: c8ef

libcxx/docs/ReleaseNotes/22.rst

@@ -67,6 +67,8 @@ Improvements and New Features
   reduced debug information.
 
 - The performance of ``std::find`` has been improved by up to 2x for integral types
+- The ``std::generate`` algorithm has been optimized for segmented iterators, resulting in a performance improvement for
+  ``std::deque<short>`` and ``std::join_view<vector<vector<short>>>`` iterators.
 
 Deprecations and Removals
 -------------------------

libcxx/include/__algorithm/generate.h

@@ -11,6 +11,7 @@
 
 #include <__algorithm/for_each.h>
 #include <__config>
+#include <__utility/forward.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -21,7 +22,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 template <class _ForwardIterator, class _Generator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
 generate(_ForwardIterator __first, _ForwardIterator __last, _Generator __gen) {
-  std::for_each(__first, __last, [&](auto& __element) { __element = __gen(); });
+  std::for_each(__first, __last, [&](auto&& __element) { std::forward<decltype(__element)>(__element) = __gen(); });
 }
 
 _LIBCPP_END_NAMESPACE_STD