[libcxx-commits] [flang] [compiler-rt] [llvm] [lldb] [clang-tools-extra] [libunwind] [clang] [libcxx] [libc] [libc++] Implement ranges::iota (PR #68494)

[Christopher Di Bella via libcxx-commits]

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@@ -0,0 +1,71 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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___NUMERIC_RANGES_IOTA_H
+#define _LIBCPP___NUMERIC_RANGES_IOTA_H
+
+#include <__algorithm/out_value_result.h>
+#include <__config>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__utility/as_const.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+namespace ranges {
+template <typename _Out, typename _Tp>
+using iota_result = ranges::out_value_result<_Out, _Tp>;
+
+namespace __ranges_iota {
+struct __iota_fn {
+private:
+  // Private helper function
+  template <class _Out, class _Sent, class _Tp>
+  _LIBCPP_HIDE_FROM_ABI static constexpr iota_result<_Out, _Tp> __iota_impl(_Out __first, _Sent __last, _Tp __value) {
+    while (__first != __last) {
+      *__first = std::as_const(__value);
+      ++__first;
+      ++__value;
+    }
+    return {std::move(__first), std::move(__value)};
+  }
----------------
cjdb wrote:

Please move this into the iterator-based `operator()` and have the range-based one call that. As it's currently implemented, additional and unnecessary moves need to happen, and we also incur some debug overhead that I'd rather avoid.

https://github.com/llvm/llvm-project/pull/68494