[libcxx-commits] [libcxx] [libc++][ranges] implement `ranges::shift_left` (PR #83231)

[via libcxx-commits]

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+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_RANGES_SHIFT_LEFT_H
+#define _LIBCPP___ALGORITHM_RANGES_SHIFT_LEFT_H
+
+#include <__algorithm/iterator_operations.h>
+#include <__algorithm/shift_left.h>
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/distance.h>
+#include <__iterator/incrementable_traits.h>
+#include <__iterator/permutable.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/subrange.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+namespace ranges {
+namespace __shift_left {
+
+struct __fn {
+  template <permutable _Iter, sentinel_for<_Iter> _Sent>
+  _LIBCPP_HIDE_FROM_ABI static constexpr subrange<_Iter>
+  operator()(_Iter __first, _Sent __last, iter_difference_t<_Iter> __n) {
+    auto __ret = std::__shift_left<_RangeAlgPolicy>(std::move(__first), std::move(__last), std::move(__n));
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huixie90 wrote:

not an issue but a question: i think we never `std::move` the `iter_difference_t`. what is the purpose of `std::move` it?

https://github.com/llvm/llvm-project/pull/83231