[libcxx-commits] [libcxx] [libc++] Merge the implementations of ranges::copy_n and std::copy_n (PR #157444)

[Louis Dionne via libcxx-commits]

================
@@ -13,48 +13,51 @@
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__type_traits/enable_if.h>
-#include <__utility/convert_to_integral.h>
+#include <__utility/move.h>
+#include <__utility/pair.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _InputIterator,
-          class _Size,
-          class _OutputIterator,
-          __enable_if_t<__has_input_iterator_category<_InputIterator>::value &&
-                            !__has_random_access_iterator_category<_InputIterator>::value,
-                        int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator
-copy_n(_InputIterator __first, _Size __orig_n, _OutputIterator __result) {
-  typedef decltype(std::__convert_to_integral(__orig_n)) _IntegralSize;
-  _IntegralSize __n = __orig_n;
-  if (__n > 0) {
+template <class _InIter,
+          class _DiffType,
+          class _OutIter,
+          __enable_if_t<__has_random_access_iterator_category<_InIter>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InIter, _OutIter>
+__copy_n(_InIter __first, _DiffType __n, _OutIter __result) {
----------------
ldionne wrote:

I think it would make sense to use `__iter_diff_t<_InIter>` here instead to clarify that these internal helpers definitely expect a real integral type. The conversion shenanigans should be handled in the public API.

https://github.com/llvm/llvm-project/pull/157444