[lib++][ranges][NFC] Refactor `iterator_operations.h` to use tags.

Change the mechanism in `iterator_operations.h` to pass around a generic
policy tag indicating whether an internal function is being invoked from
a "classic" STL algorithm or a ranges algorithm. `IterOps` is now
a template class specialized on the policy tag.

The advantage is that this mechanism is more generic and allows defining
arbitrary conditions in a clean manner.

Also add a few more iterator functions to `IterOps`.

Differential Revision: https://reviews.llvm.org/D129390

1 files changed, 46 insertions, 12 deletions

diff --git a/libcxx/include/__algorithm/iterator_operations.h b/libcxx/include/__algorithm/iterator_operations.h
index 3d86f35f5998..bccac368f302 100644
--- a/libcxx/include/__algorithm/iterator_operations.h
+++ b/libcxx/include/__algorithm/iterator_operations.h
@@ -6,14 +6,20 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___ALGORIHTM_ITERATOR_OPERATIONS_H
-#define _LIBCPP___ALGORIHTM_ITERATOR_OPERATIONS_H
+#ifndef _LIBCPP___ALGORITHM_ITERATOR_OPERATIONS_H
+#define _LIBCPP___ALGORITHM_ITERATOR_OPERATIONS_H
 
+#include <__algorithm/iter_swap.h>
 #include <__config>
 #include <__iterator/advance.h>
 #include <__iterator/distance.h>
+#include <__iterator/iter_move.h>
+#include <__iterator/iter_swap.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/next.h>
+#include <__utility/forward.h>
+#include <__utility/move.h>
+#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -21,35 +27,63 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+template <class _AlgPolicy> struct _IterOps;
+
 #if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
-struct _RangesIterOps {
+struct _RangeAlgPolicy {};
+
+template <>
+struct _IterOps<_RangeAlgPolicy> {
   static constexpr auto advance = ranges::advance;
   static constexpr auto distance = ranges::distance;
+  static constexpr auto __iter_move = ranges::iter_move;
+  static constexpr auto iter_swap = ranges::iter_swap;
   static constexpr auto next = ranges::next;
 };
 #endif
 
-struct _StdIterOps {
+struct _ClassicAlgPolicy {};
+
+template <>
+struct _IterOps<_ClassicAlgPolicy> {
 
-  template <class _Iterator, class _Distance>
-  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_AFTER_CXX11 void advance(_Iterator& __iter, _Distance __count) {
-    return std::advance(__iter, __count);
+  // advance
+  template <class _Iter, class _Distance>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
+  static void advance(_Iter& __iter, _Distance __count) {
+    std::advance(__iter, __count);
   }
 
-  template <class _Iterator>
-  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_AFTER_CXX11
-  typename iterator_traits<_Iterator>::difference_type distance(_Iterator __first, _Iterator __last) {
+  // distance
+  template <class _Iter>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
+  static typename iterator_traits<_Iter>::difference_type distance(_Iter __first, _Iter __last) {
     return std::distance(__first, __last);
   }
 
+  // iter_move
+  template <class _Iter>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
+  // Declaring the return type is necessary for the C++03 mode (which doesn't support placeholder return types).
+  static typename iterator_traits<__uncvref_t<_Iter> >::value_type&& __iter_move(_Iter&& __i) {
+    return std::move(*std::forward<_Iter>(__i));
+  }
+
+  // iter_swap
+  template <class _Iter1, class _Iter2>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
+  static void iter_swap(_Iter1&& __a, _Iter2&& __b) {
+    std::iter_swap(std::forward<_Iter1>(__a), std::forward<_Iter2>(__b));
+  }
+
+  // next
   template <class _Iterator>
   _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_AFTER_CXX11
   _Iterator next(_Iterator, _Iterator __last) {
     return __last;
   }
-
 };
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP___ALGORIHTM_ITERATOR_OPERATIONS_H
+#endif // _LIBCPP___ALGORITHM_ITERATOR_OPERATIONS_H