[compiler-rt] [libc++] Implement ranges::iota (PR #68494)

James E T Smith via llvm-commits llvm-commits at lists.llvm.org
Sat Oct 7 11:51:52 PDT 2023


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

# Overview

As a disclaimer, this is my first PR to LLVM and while I've tried to ensure I've followed the LLVM and libc++ contributing guidelines, there's probably a good chance I missed something. If I have, just let me know and I'll try to correct it as soon as I can.

This PR implements `std::ranges::iota` and `std::ranges::out_value_result` outlined in [P2440r1](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2440r1.html).

As outlined in the paper above, I've:
- Implemented `out_value_result` and added to `<algorithm>`
- Added `out_value_result`, `iota_result`, and two overloads of `iota`  to `std::ranges` in `<numeric>`
- Updated the version macro `__cpp_lib_ranges_iota` in `<version>`

I've also added tests for `ranges::iota` and `ranges::out_value_result`. Lastly, I added those structs to the appropriate module files.

# TODOs
- [ ] Updating the range [status doc](https://github.com/jamesETsmith/llvm-project/blob/main/libcxx/docs/Status/RangesMajorFeatures.csv) 
- [ ] I'm open to implementing the rest of P2440r1 (`ranges::shift_left` and `ranges::shift_right`) if that's ok, I just wanted to get feedback on `ranges::iota` first
- [ ] I've been having trouble building the modules locally and want to make sure that's working properly

>From c4a3ccfbad090ad8314aa8ad53092edc8d5432bc Mon Sep 17 00:00:00 2001
From: James Smith <james.smith9113 at gmail.com>
Date: Thu, 28 Sep 2023 10:11:15 -0400
Subject: [PATCH 1/6] [libc++] Implement ranges::iota and
 ranges::out_value_result

---
 libcxx/include/CMakeLists.txt                 |   2 +
 libcxx/include/__algorithm/out_value_result.h |  52 +++++++++
 libcxx/include/__numeric/ranges_iota.h        |  53 +++++++++
 libcxx/include/algorithm                      |   4 +
 libcxx/include/numeric                        |   1 +
 libcxx/include/version                        |   2 +-
 .../out_value_result.pass.cpp                 | 102 ++++++++++++++++++
 .../numeric.iota/ranges.iota.pass.cpp         |  52 +++++++++
 8 files changed, 267 insertions(+), 1 deletion(-)
 create mode 100644 libcxx/include/__algorithm/out_value_result.h
 create mode 100644 libcxx/include/__numeric/ranges_iota.h
 create mode 100644 libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp
 create mode 100644 libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 2ec755236dbaee2..c6eb03f1d68e984 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -63,6 +63,7 @@ set(files
   __algorithm/next_permutation.h
   __algorithm/none_of.h
   __algorithm/nth_element.h
+  __algorithm/out_value_result.h
   __algorithm/partial_sort.h
   __algorithm/partial_sort_copy.h
   __algorithm/partition.h
@@ -561,6 +562,7 @@ set(files
   __numeric/partial_sum.h
   __numeric/pstl_reduce.h
   __numeric/pstl_transform_reduce.h
+  __numeric/ranges_iota.h
   __numeric/reduce.h
   __numeric/transform_exclusive_scan.h
   __numeric/transform_inclusive_scan.h
diff --git a/libcxx/include/__algorithm/out_value_result.h b/libcxx/include/__algorithm/out_value_result.h
new file mode 100644
index 000000000000000..8baffec7b9ef4da
--- /dev/null
+++ b/libcxx/include/__algorithm/out_value_result.h
@@ -0,0 +1,52 @@
+// -*- 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___ALGORITHM_OUT_VALUE_RESULT_H
+#define _LIBCPP___ALGORITHM_OUT_VALUE_RESULT_H
+
+#include <__concepts/convertible_to.h>
+#include <__config>
+#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 {
+
+template <class _OutIter1, class _ValType1>
+struct out_value_result {
+  _LIBCPP_NO_UNIQUE_ADDRESS _OutIter1 out;
+  _LIBCPP_NO_UNIQUE_ADDRESS _ValType1 value;
+
+  template <class _OutIter2, class _ValType2>
+    requires convertible_to<const _OutIter1&, _OutIter2> && convertible_to<const _ValType1&, _ValType2>
+  constexpr operator out_value_result<_OutIter2, _ValType2>() const& { return {out, value}; }
+
+  template <class _OutIter2, class _ValType2>
+    requires convertible_to<_OutIter1, _OutIter2> && convertible_to<_ValType1, _ValType2>
+  constexpr operator out_value_result<_OutIter2, _ValType2>() && { return {std::move(out), std::move(value)}; }
+};
+
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_OUT_VALUE_RESULT_H
diff --git a/libcxx/include/__numeric/ranges_iota.h b/libcxx/include/__numeric/ranges_iota.h
new file mode 100644
index 000000000000000..20311a68c2a348c
--- /dev/null
+++ b/libcxx/include/__numeric/ranges_iota.h
@@ -0,0 +1,53 @@
+// -*- 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/concepts.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>;
+
+struct __iota_fn {
+  template <input_or_output_iterator _Out, sentinel_for<_Out> _Sent, weakly_incrementable _Tp>
+    requires indirectly_writable<_Out, const _Tp&>
+  constexpr iota_result<_Out, _Tp> operator()(_Out __first, _Sent __last, _Tp __value) const {
+    while (__first != __last) {
+      *__first = static_cast<const _Tp&>(__value);
+      ++__first;
+      ++__value;
+    }
+    return {std::move(__first), std::move(__value)};
+  }
+
+  template <weakly_incrementable _Tp, ranges::output_range<const _Tp&> _Range>
+  constexpr iota_result<ranges::borrowed_iterator_t<_Range>, _Tp> operator()(_Range&& __r, _Tp __value) const {
+    return (*this)(ranges::begin(__r), ranges::end(__r), std::move(__value));
+  }
+};
+
+inline constexpr __iota_fn iota{};
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___NUMERIC_RANGES_IOTA_H
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 69ba9537dda6984..42f01a99a02cc93 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -42,6 +42,9 @@ namespace ranges {
   template <class I>
     struct in_found_result;              // since C++20
 
+  template <class O, class T>
+    struct out_value_result;             // since C++23
+
   template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
     indirect_strict_weak_order<projected<I, Proj>> Comp = ranges::less>                                   // since C++20
   constexpr I min_element(I first, S last, Comp comp = {}, Proj proj = {});
@@ -1817,6 +1820,7 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/next_permutation.h>
 #include <__algorithm/none_of.h>
 #include <__algorithm/nth_element.h>
+#include <__algorithm/out_value_result.h>
 #include <__algorithm/partial_sort.h>
 #include <__algorithm/partial_sort_copy.h>
 #include <__algorithm/partition.h>
diff --git a/libcxx/include/numeric b/libcxx/include/numeric
index 3fcf6cefdb4b884..363dfd229df54dc 100644
--- a/libcxx/include/numeric
+++ b/libcxx/include/numeric
@@ -160,6 +160,7 @@ template<class T>
 #include <__numeric/partial_sum.h>
 #include <__numeric/pstl_reduce.h>
 #include <__numeric/pstl_transform_reduce.h>
+#include <__numeric/ranges_iota.h>
 #include <__numeric/reduce.h>
 #include <__numeric/transform_exclusive_scan.h>
 #include <__numeric/transform_inclusive_scan.h>
diff --git a/libcxx/include/version b/libcxx/include/version
index e5a995366a7aa48..164c60dfd6af6d4 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -436,7 +436,7 @@ __cpp_lib_within_lifetime                               202306L <type_traits>
 # define __cpp_lib_ranges_as_rvalue                     202207L
 // # define __cpp_lib_ranges_chunk                         202202L
 # define __cpp_lib_ranges_chunk_by                      202202L
-// # define __cpp_lib_ranges_iota                          202202L
+# define __cpp_lib_ranges_iota                          202202L
 // # define __cpp_lib_ranges_join_with                     202202L
 # define __cpp_lib_ranges_repeat                        202207L
 // # define __cpp_lib_ranges_slide                         202202L
diff --git a/libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp b/libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp
new file mode 100644
index 000000000000000..189149b0b4acb0c
--- /dev/null
+++ b/libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp
@@ -0,0 +1,102 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, C++20
+
+//  template <class O, class T>
+//    struct out_value_result;
+
+#include <algorithm>
+#include <cassert>
+#include <type_traits>
+
+#include "MoveOnly.h"
+
+struct A {
+  explicit A(int);
+};
+// no implicit conversion
+static_assert(!std::is_constructible_v<std::ranges::out_value_result<A, A>, std::ranges::out_value_result<int, int>>);
+
+struct B {
+  B(int);
+};
+// implicit conversion
+static_assert(std::is_constructible_v<std::ranges::out_value_result<B, B>, std::ranges::out_value_result<int, int>>);
+static_assert(std::is_constructible_v<std::ranges::out_value_result<B, B>, std::ranges::out_value_result<int, int>&>);
+static_assert(
+    std::is_constructible_v<std::ranges::out_value_result<B, B>, const std::ranges::out_value_result<int, int>>);
+static_assert(
+    std::is_constructible_v<std::ranges::out_value_result<B, B>, const std::ranges::out_value_result<int, int>&>);
+
+struct C {
+  C(int&);
+};
+static_assert(!std::is_constructible_v<std::ranges::out_value_result<C, C>, std::ranges::out_value_result<int, int>&>);
+
+// has to be convertible via const&
+static_assert(
+    std::is_convertible_v<std::ranges::out_value_result<int, int>&, std::ranges::out_value_result<long, long>>);
+static_assert(
+    std::is_convertible_v<const std::ranges::out_value_result<int, int>&, std::ranges::out_value_result<long, long>>);
+static_assert(
+    std::is_convertible_v<std::ranges::out_value_result<int, int>&&, std::ranges::out_value_result<long, long>>);
+static_assert(
+    std::is_convertible_v<const std::ranges::out_value_result<int, int>&&, std::ranges::out_value_result<long, long>>);
+
+// should be move constructible
+static_assert(std::is_move_constructible_v<std::ranges::out_value_result<MoveOnly, int>>);
+static_assert(std::is_move_constructible_v<std::ranges::out_value_result<int, MoveOnly>>);
+
+struct NotConvertible {};
+// conversions should not work if there is no conversion
+static_assert(!std::is_convertible_v<std::ranges::out_value_result<NotConvertible, int>,
+                                     std::ranges::out_value_result<int, NotConvertible>>);
+static_assert(!std::is_convertible_v<std::ranges::out_value_result<int, NotConvertible>,
+                                     std::ranges::out_value_result<NotConvertible, int>>);
+
+template <class T>
+struct ConvertibleFrom {
+  constexpr ConvertibleFrom(T c) : content{c} {}
+  T content;
+};
+
+constexpr bool test() {
+  {
+    std::ranges::out_value_result<double, int> res{10, 1};
+    assert(res.out == 10);
+    assert(res.value == 1);
+    std::ranges::out_value_result<ConvertibleFrom<double>, ConvertibleFrom<int>> res2 = res;
+    assert(res2.out.content == 10);
+    assert(res2.value.content == 1);
+  }
+  {
+    std::ranges::out_value_result<MoveOnly, int> res{MoveOnly{}, 10};
+    assert(res.out.get() == 1);
+    assert(res.value == 10);
+    auto res2 = std::move(res);
+    assert(res.out.get() == 0);
+    assert(res.value == 10);
+    assert(res2.out.get() == 1);
+    assert(res2.value == 10);
+  }
+  {
+    auto [min, max] = std::ranges::out_value_result<int, int>{1, 2};
+    assert(min == 1);
+    assert(max == 2);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
new file mode 100644
index 000000000000000..1e2a6970adb35e3
--- /dev/null
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
@@ -0,0 +1,52 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// Testing std::ranges::iota
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+#include <cassert>
+#include <numeric>
+#include <array>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+
+// This is pulled directly from the std::iota test
+template <class InIter>
+TEST_CONSTEXPR_CXX20 void test0() {
+  int ia[]         = {1, 2, 3, 4, 5};
+  int ir[]         = {5, 6, 7, 8, 9};
+  const unsigned s = sizeof(ia) / sizeof(ia[0]);
+  std::ranges::iota(InIter(ia), InIter(ia + s), 5);
+  for (unsigned i = 0; i < s; ++i)
+    assert(ia[i] == ir[i]);
+}
+
+TEST_CONSTEXPR_CXX20 bool test0() {
+  test0<forward_iterator<int*> >();
+  test0<bidirectional_iterator<int*> >();
+  test0<random_access_iterator<int*> >();
+  test0<int*>();
+
+  return true;
+}
+
+TEST_CONSTEXPR_CXX20 void test1() {
+  std::array<int, 5> ia = {1, 2, 3, 4, 5};
+  std::array<int, 5> ir = {5, 6, 7, 8, 9};
+  std::ranges::iota(ia, 5);
+  for (unsigned i = 0; i < ir.size(); ++i)
+    assert(ia[i] == ir[i]);
+}
+
+int main(int, char**) {
+  test0();
+  test1();
+  return 0;
+}
\ No newline at end of file

>From 574c94ce4f7eed06013a5e5d1460da1d148cc7cd Mon Sep 17 00:00:00 2001
From: James Smith <james.smith9113 at gmail.com>
Date: Fri, 29 Sep 2023 14:11:49 -0400
Subject: [PATCH 2/6] [libc++] Implement ranges::iota: update module and docs
 info

---
 libcxx/docs/FeatureTestMacroTable.rst                  | 2 +-
 libcxx/include/module.modulemap.in                     | 1 +
 libcxx/modules/std/numeric.inc                         | 8 ++++++--
 libcxx/utils/generate_feature_test_macro_components.py | 1 -
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index e1b4172b22c53da..ebb18dc7bed9bd2 100644
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -348,7 +348,7 @@ Status
     --------------------------------------------------- -----------------
     ``__cpp_lib_ranges_chunk_by``                       ``202202L``
     --------------------------------------------------- -----------------
-    ``__cpp_lib_ranges_iota``                           *unimplemented*
+    ``__cpp_lib_ranges_iota``                           ``202202L``
     --------------------------------------------------- -----------------
     ``__cpp_lib_ranges_join_with``                      *unimplemented*
     --------------------------------------------------- -----------------
diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in
index 6d9bb8653fcb5e9..b092cc7c0e93bf1 100644
--- a/libcxx/include/module.modulemap.in
+++ b/libcxx/include/module.modulemap.in
@@ -1602,6 +1602,7 @@ module std_private_numeric_pstl_transform_reduce    [system] {
   export *
 }
 module std_private_numeric_reduce                   [system] { header "__numeric/reduce.h" }
+module std_private_numeric_ranges_iota              [system] { header "__numeric/ranges_iota.h" }
 module std_private_numeric_transform_exclusive_scan [system] { header "__numeric/transform_exclusive_scan.h" }
 module std_private_numeric_transform_inclusive_scan [system] { header "__numeric/transform_inclusive_scan.h" }
 module std_private_numeric_transform_reduce         [system] { header "__numeric/transform_reduce.h" }
diff --git a/libcxx/modules/std/numeric.inc b/libcxx/modules/std/numeric.inc
index d2b7688d4e5f10a..9204e8d8715935d 100644
--- a/libcxx/modules/std/numeric.inc
+++ b/libcxx/modules/std/numeric.inc
@@ -42,8 +42,12 @@ export namespace std {
   using std::iota;
 
   namespace ranges {
-    // using std::ranges::iota_result;
-    // using std::ranges::iota;
+
+#if _LIBCPP_STD_VER >= 23
+    using std::ranges::iota;
+    using std::ranges::iota_result;
+#endif // _LIBCPP_STD_VER >= 23
+
   } // namespace ranges
 
   // [numeric.ops.gcd], greatest common divisor
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index ac342aff0beb701..9fd50d66edbe317 100755
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -806,7 +806,6 @@ def add_version_header(tc):
             "name": "__cpp_lib_ranges_iota",
             "values": {"c++23": 202202},
             "headers": ["numeric"],
-            "unimplemented": True,
         },
         {
             "name": "__cpp_lib_ranges_join_with",

>From e4cfe00cb1b348d5a3515ef907c7c87334c6824c Mon Sep 17 00:00:00 2001
From: James Smith <james.smith9113 at gmail.com>
Date: Fri, 29 Sep 2023 16:50:46 -0400
Subject: [PATCH 3/6] [libc++] Implement ranges::iota: fixing formatting issues
 for out_value_result

---
 libcxx/include/__algorithm/out_value_result.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/libcxx/include/__algorithm/out_value_result.h b/libcxx/include/__algorithm/out_value_result.h
index 8baffec7b9ef4da..a99d206f7035ff2 100644
--- a/libcxx/include/__algorithm/out_value_result.h
+++ b/libcxx/include/__algorithm/out_value_result.h
@@ -34,11 +34,15 @@ struct out_value_result {
 
   template <class _OutIter2, class _ValType2>
     requires convertible_to<const _OutIter1&, _OutIter2> && convertible_to<const _ValType1&, _ValType2>
-  constexpr operator out_value_result<_OutIter2, _ValType2>() const& { return {out, value}; }
+  constexpr operator out_value_result<_OutIter2, _ValType2>() const& {
+    return {out, value};
+  }
 
   template <class _OutIter2, class _ValType2>
     requires convertible_to<_OutIter1, _OutIter2> && convertible_to<_ValType1, _ValType2>
-  constexpr operator out_value_result<_OutIter2, _ValType2>() && { return {std::move(out), std::move(value)}; }
+  constexpr operator out_value_result<_OutIter2, _ValType2>() && {
+    return {std::move(out), std::move(value)};
+  }
 };
 
 } // namespace ranges

>From 7cdfea2d5acf553345ee0c506ce9e3914cbb3ed0 Mon Sep 17 00:00:00 2001
From: James Smith <james.smith9113 at gmail.com>
Date: Sat, 7 Oct 2023 12:04:32 -0400
Subject: [PATCH 4/6] [libc++] Implement ranges::iota: Cleaning up tests for
 ranges::iota and out_value_result. Updating Cxx23Papers.csv too.

---
 libcxx/docs/Status/Cxx23Papers.csv            |   2 +-
 libcxx/include/__numeric/ranges_iota.h        |   3 +-
 libcxx/modules/std/algorithm.inc              |   2 +-
 .../out_value_result.pass.cpp                 | 104 ++++++++++------
 .../numeric.iota/ranges.iota.pass.cpp         | 117 ++++++++++++++++--
 5 files changed, 171 insertions(+), 57 deletions(-)

diff --git a/libcxx/docs/Status/Cxx23Papers.csv b/libcxx/docs/Status/Cxx23Papers.csv
index 9cb49fd5176ea5f..4618908cfb73941 100644
--- a/libcxx/docs/Status/Cxx23Papers.csv
+++ b/libcxx/docs/Status/Cxx23Papers.csv
@@ -46,7 +46,7 @@
 "`P2255R2 <https://wg21.link/P2255R2>`__","LWG","A type trait to detect reference binding to temporary","February 2022","",""
 "`P2273R3 <https://wg21.link/P2273R3>`__","LWG","Making ``std::unique_ptr`` constexpr","February 2022","|Complete|","16.0"
 "`P2387R3 <https://wg21.link/P2387R3>`__","LWG","Pipe support for user-defined range adaptors","February 2022","","","|ranges|"
-"`P2440R1 <https://wg21.link/P2440R1>`__","LWG","``ranges::iota``, ``ranges::shift_left`` and ``ranges::shift_right``","February 2022","","","|ranges|"
+"`P2440R1 <https://wg21.link/P2440R1>`__","LWG","``ranges::iota``, ``ranges::shift_left`` and ``ranges::shift_right``","February 2022","|In progress|","","|ranges|"
 "`P2441R2 <https://wg21.link/P2441R2>`__","LWG","``views::join_with``","February 2022","","","|ranges|"
 "`P2442R1 <https://wg21.link/P2442R1>`__","LWG","Windowing range adaptors: ``views::chunk`` and ``views::slide``","February 2022","","","|ranges|"
 "`P2443R1 <https://wg21.link/P2443R1>`__","LWG","``views::chunk_by``","February 2022","|Complete|","18.0","|ranges|"
diff --git a/libcxx/include/__numeric/ranges_iota.h b/libcxx/include/__numeric/ranges_iota.h
index 20311a68c2a348c..a8c069832da7e6d 100644
--- a/libcxx/include/__numeric/ranges_iota.h
+++ b/libcxx/include/__numeric/ranges_iota.h
@@ -13,6 +13,7 @@
 #include <__algorithm/out_value_result.h>
 #include <__config>
 #include <__ranges/concepts.h>
+#include <__utility/as_const.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -30,7 +31,7 @@ struct __iota_fn {
     requires indirectly_writable<_Out, const _Tp&>
   constexpr iota_result<_Out, _Tp> operator()(_Out __first, _Sent __last, _Tp __value) const {
     while (__first != __last) {
-      *__first = static_cast<const _Tp&>(__value);
+      *__first = std::as_const(__value);
       ++__first;
       ++__value;
     }
diff --git a/libcxx/modules/std/algorithm.inc b/libcxx/modules/std/algorithm.inc
index b7900d15c10c2b5..62ce8cf02c14f95 100644
--- a/libcxx/modules/std/algorithm.inc
+++ b/libcxx/modules/std/algorithm.inc
@@ -18,7 +18,7 @@ export namespace std {
     using std::ranges::in_out_result;
     // using std::ranges::in_value_result;
     using std::ranges::min_max_result;
-    // using std::ranges::out_value_result;
+    using std::ranges::out_value_result;
   } // namespace ranges
 
   // [alg.nonmodifying], non-modifying sequence operations
diff --git a/libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp b/libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp
index 189149b0b4acb0c..3a930bb063f975f 100644
--- a/libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp
+++ b/libcxx/test/std/algorithms/algorithms.results/out_value_result.pass.cpp
@@ -17,48 +17,25 @@
 
 #include "MoveOnly.h"
 
-struct A {
-  explicit A(int);
+//
+// Helper structs
+//
+
+// only explicit construction
+struct IterTypeExplicit {
+  explicit IterTypeExplicit(int*);
 };
-// no implicit conversion
-static_assert(!std::is_constructible_v<std::ranges::out_value_result<A, A>, std::ranges::out_value_result<int, int>>);
 
-struct B {
-  B(int);
+// implicit construction
+struct IterTypeImplicit {
+  IterTypeImplicit(int*);
 };
-// implicit conversion
-static_assert(std::is_constructible_v<std::ranges::out_value_result<B, B>, std::ranges::out_value_result<int, int>>);
-static_assert(std::is_constructible_v<std::ranges::out_value_result<B, B>, std::ranges::out_value_result<int, int>&>);
-static_assert(
-    std::is_constructible_v<std::ranges::out_value_result<B, B>, const std::ranges::out_value_result<int, int>>);
-static_assert(
-    std::is_constructible_v<std::ranges::out_value_result<B, B>, const std::ranges::out_value_result<int, int>&>);
-
-struct C {
-  C(int&);
+
+struct IterTypeImplicitRef {
+  IterTypeImplicitRef(int&);
 };
-static_assert(!std::is_constructible_v<std::ranges::out_value_result<C, C>, std::ranges::out_value_result<int, int>&>);
-
-// has to be convertible via const&
-static_assert(
-    std::is_convertible_v<std::ranges::out_value_result<int, int>&, std::ranges::out_value_result<long, long>>);
-static_assert(
-    std::is_convertible_v<const std::ranges::out_value_result<int, int>&, std::ranges::out_value_result<long, long>>);
-static_assert(
-    std::is_convertible_v<std::ranges::out_value_result<int, int>&&, std::ranges::out_value_result<long, long>>);
-static_assert(
-    std::is_convertible_v<const std::ranges::out_value_result<int, int>&&, std::ranges::out_value_result<long, long>>);
-
-// should be move constructible
-static_assert(std::is_move_constructible_v<std::ranges::out_value_result<MoveOnly, int>>);
-static_assert(std::is_move_constructible_v<std::ranges::out_value_result<int, MoveOnly>>);
 
 struct NotConvertible {};
-// conversions should not work if there is no conversion
-static_assert(!std::is_convertible_v<std::ranges::out_value_result<NotConvertible, int>,
-                                     std::ranges::out_value_result<int, NotConvertible>>);
-static_assert(!std::is_convertible_v<std::ranges::out_value_result<int, NotConvertible>,
-                                     std::ranges::out_value_result<NotConvertible, int>>);
 
 template <class T>
 struct ConvertibleFrom {
@@ -66,6 +43,51 @@ struct ConvertibleFrom {
   T content;
 };
 
+//
+constexpr void test_constraints() {
+  // requires convertible_to<const _OutIter1&, _OutIter2> && convertible_to<const _ValType1&, _ValType2>
+  static_assert(
+      std::is_constructible_v<std::ranges::out_value_result<int*, int>, std::ranges::out_value_result<int*, int>>);
+
+  // test failure when implicit conversion isn't allowed
+  static_assert(!std::is_constructible_v<std::ranges::out_value_result<IterTypeExplicit, int>,
+                                         std::ranges::out_value_result<int*, int>>);
+
+  // test success when implicit conversion is allowed, checking combinations of value, reference, and const
+  static_assert(std::is_constructible_v<std::ranges::out_value_result<IterTypeImplicit, int>,
+                                        std::ranges::out_value_result<int*, int>>);
+  static_assert(std::is_constructible_v<std::ranges::out_value_result<IterTypeImplicit, int>,
+                                        std::ranges::out_value_result<int*, int> const>);
+  static_assert(std::is_constructible_v<std::ranges::out_value_result<IterTypeImplicit, int>,
+                                        std::ranges::out_value_result<int*, int>&>);
+  static_assert(std::is_constructible_v<std::ranges::out_value_result<IterTypeImplicit, int>,
+                                        std::ranges::out_value_result<int*, int> const&>);
+
+  static_assert(!std::is_constructible_v<std::ranges::out_value_result<IterTypeImplicitRef, int>,
+                                         std::ranges::out_value_result<int, int>&>);
+
+  // has to be convertible via const&
+  static_assert(
+      std::is_convertible_v<std::ranges::out_value_result<int, int>&, std::ranges::out_value_result<long, long>>);
+  static_assert(
+      std::is_convertible_v<const std::ranges::out_value_result<int, int>&, std::ranges::out_value_result<long, long>>);
+  static_assert(
+      std::is_convertible_v<std::ranges::out_value_result<int, int>&&, std::ranges::out_value_result<long, long>>);
+  static_assert(std::is_convertible_v<const std::ranges::out_value_result<int, int>&&,
+                                      std::ranges::out_value_result<long, long>>);
+
+  // should be move constructible
+  static_assert(std::is_move_constructible_v<std::ranges::out_value_result<MoveOnly, int>>);
+  static_assert(std::is_move_constructible_v<std::ranges::out_value_result<int, MoveOnly>>);
+
+  // conversions should not work if there is no conversion
+  static_assert(!std::is_convertible_v<std::ranges::out_value_result<NotConvertible, int>,
+                                       std::ranges::out_value_result<int, NotConvertible>>);
+  static_assert(!std::is_convertible_v<std::ranges::out_value_result<int, NotConvertible>,
+                                       std::ranges::out_value_result<NotConvertible, int>>);
+}
+
+// Test results
 constexpr bool test() {
   {
     std::ranges::out_value_result<double, int> res{10, 1};
@@ -86,17 +108,17 @@ constexpr bool test() {
     assert(res2.value == 10);
   }
   {
-    auto [min, max] = std::ranges::out_value_result<int, int>{1, 2};
-    assert(min == 1);
-    assert(max == 2);
+    auto [out, val] = std::ranges::out_value_result<int, int>{1, 2};
+    assert(out == 1);
+    assert(val == 2);
   }
 
   return true;
 }
 
 int main(int, char**) {
+  test_constraints();
   test();
   static_assert(test());
-
   return 0;
-}
+}
\ No newline at end of file
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
index 1e2a6970adb35e3..85f99942e97b2ac 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
@@ -12,41 +12,132 @@
 
 #include <cassert>
 #include <numeric>
+#include <algorithm>
 #include <array>
 
 #include "test_macros.h"
 #include "test_iterators.h"
+#include "almost_satisfies_types.h"
+
+// Concepts to check different overloads of std::ranges::iota
+template <class Iter = int*, class Sent = int*, class Value = int>
+concept HasIotaIter = requires(Iter&& iter, Sent&& sent, Value&& val) {
+  std::ranges::iota(std::forward<Iter>(iter), std::forward<Sent>(sent), std::forward<Value>(val));
+};
+
+template <class Range, class Value = int>
+concept HasIotaRange = requires(Range&& range, Value&& val) {
+  std::ranges::iota(std::forward<Range>(range), std::forward<Value>(val));
+};
+
+constexpr void test_constraints() {
+  // Test constraints of the iterator/sentinel overload
+  // ==================================================
+  static_assert(HasIotaIter<int*, int*, int>);
+
+  // !input_or_output_iterator<O>
+  static_assert(!HasIotaIter<InputIteratorNotInputOrOutputIterator>);
+
+  // !sentinel_for<S, O>
+  static_assert(!HasIotaIter<int*, SentinelForNotSemiregular>);
+  static_assert(!HasIotaIter<int*, SentinelForNotWeaklyEqualityComparableWith>);
+
+  // !weakly_incrementable<T>
+  static_assert(!HasIotaIter<int*, int*, WeaklyIncrementableNotMovable>);
+
+  // !indirectly writable <O, T>
+  static_assert(!HasIotaIter<OutputIteratorNotIndirectlyWritable, int*, int>);
+
+  // Test constraints for the range overload
+  // =======================================
+  static_assert(HasIotaRange<UncheckedRange<int*>, int>);
+
+  // !weakly_incrementable<T>
+  static_assert(!HasIotaRange<UncheckedRange<int*>, WeaklyIncrementableNotMovable>);
+
+  // !ranges::output_range<const _Tp&>
+  static_assert(!HasIotaRange<UncheckedRange<int*>, OutputIteratorNotIndirectlyWritable>);
+}
 
 // This is pulled directly from the std::iota test
-template <class InIter>
-TEST_CONSTEXPR_CXX20 void test0() {
+template <class InOutIter, class Sent = InOutIter>
+constexpr void test0() {
   int ia[]         = {1, 2, 3, 4, 5};
   int ir[]         = {5, 6, 7, 8, 9};
   const unsigned s = sizeof(ia) / sizeof(ia[0]);
-  std::ranges::iota(InIter(ia), InIter(ia + s), 5);
-  for (unsigned i = 0; i < s; ++i)
-    assert(ia[i] == ir[i]);
+  std::ranges::iota(InOutIter(ia), InOutIter(ia + s), 5);
+  assert(std::ranges::equal(ia, ir));
 }
 
-TEST_CONSTEXPR_CXX20 bool test0() {
+constexpr bool test0() {
+  // TODO why don't these work?
+  // test0<cpp17_input_iterator<int*>, sentinel_wrapper<cpp17_input_iterator<int*>>>();
+  // test0<cpp20_input_iterator<int*>, sentinel_wrapper<cpp20_input_iterator<int*>>>();
+  // test0<cpp17_output_iterator<int*>, sentinel_wrapper<cpp17_output_iterator<int*>>>();
+  // test0<cpp20_output_iterator<int*>, sentinel_wrapper<cpp20_output_iterator<int*>>>();
   test0<forward_iterator<int*> >();
   test0<bidirectional_iterator<int*> >();
   test0<random_access_iterator<int*> >();
+  test0<contiguous_iterator<int*>>();
   test0<int*>();
 
   return true;
 }
 
-TEST_CONSTEXPR_CXX20 void test1() {
-  std::array<int, 5> ia = {1, 2, 3, 4, 5};
-  std::array<int, 5> ir = {5, 6, 7, 8, 9};
-  std::ranges::iota(ia, 5);
-  for (unsigned i = 0; i < ir.size(); ++i)
-    assert(ia[i] == ir[i]);
+template <class Iter, class Sent, std::size_t N>
+constexpr void test_result(std::array<int, N> input, int starting_value, std::array<int, N> const expected) {
+  { // (iterator, sentinel) overload
+    auto in_begin = Iter(input.data());
+    auto in_end   = Sent(Iter(input.data() + input.size()));
+    std::same_as<std::ranges::out_value_result<Iter, int>> decltype(auto) result =
+        std::ranges::iota(std::move(in_begin), std::move(in_end), starting_value);
+    assert(result.out == in_end);
+    if constexpr (expected.size() > 0) {
+      assert(result.value == expected.back() + 1);
+    } else {
+      assert(result.value == starting_value);
+    }
+    assert(std::ranges::equal(input, expected));
+  }
+
+  { // (range) overload
+    auto in_begin = Iter(input.data());
+    auto in_end   = Sent(Iter(input.data() + input.size()));
+    auto range    = std::ranges::subrange(std::move(in_begin), std::move(in_end));
+
+    std::same_as<std::ranges::out_value_result<Iter, int>> decltype(auto) result =
+        std::ranges::iota(range, starting_value);
+    assert(result.out == in_end);
+    if constexpr (expected.size() > 0) {
+      assert(result.value == expected.back() + 1);
+    } else {
+      assert(result.value == starting_value);
+    }
+    assert(std::ranges::equal(input, expected));
+  }
+}
+
+constexpr bool test_results() {
+  using Iter = forward_iterator<int*>;
+  using Sent = sentinel_wrapper<Iter>;
+
+  // Empty
+  test_result<Iter, Sent, 0>({}, 0, {});
+  // 1-element sequence
+  test_result<Iter, Sent, 1>({1}, 0, {0});
+  // Longer sequence
+  test_result<Iter, Sent, 5>({1, 2, 3, 4, 5}, 0, {0, 1, 2, 3, 4});
+
+  return true;
 }
 
 int main(int, char**) {
+  test_constraints();
+
   test0();
-  test1();
+  static_assert(test0());
+
+  test_results();
+  static_assert(test_results());
   return 0;
 }
\ No newline at end of file

>From a1d015c2affa40bb5f5313cdaed46c5a8cd4b243 Mon Sep 17 00:00:00 2001
From: James Smith <james.smith9113 at gmail.com>
Date: Sat, 7 Oct 2023 12:35:20 -0400
Subject: [PATCH 5/6] [libc++] Implement ranges::iota: Cleaning up tests for
 ranges::iota and adding testing for more iterators

---
 .../numeric.iota/ranges.iota.pass.cpp         | 53 ++++++-------------
 1 file changed, 17 insertions(+), 36 deletions(-)

diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
index 85f99942e97b2ac..611293debbf731b 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
@@ -59,31 +59,6 @@ constexpr void test_constraints() {
   static_assert(!HasIotaRange<UncheckedRange<int*>, OutputIteratorNotIndirectlyWritable>);
 }
 
-// This is pulled directly from the std::iota test
-template <class InOutIter, class Sent = InOutIter>
-constexpr void test0() {
-  int ia[]         = {1, 2, 3, 4, 5};
-  int ir[]         = {5, 6, 7, 8, 9};
-  const unsigned s = sizeof(ia) / sizeof(ia[0]);
-  std::ranges::iota(InOutIter(ia), InOutIter(ia + s), 5);
-  assert(std::ranges::equal(ia, ir));
-}
-
-constexpr bool test0() {
-  // TODO why don't these work?
-  // test0<cpp17_input_iterator<int*>, sentinel_wrapper<cpp17_input_iterator<int*>>>();
-  // test0<cpp20_input_iterator<int*>, sentinel_wrapper<cpp20_input_iterator<int*>>>();
-  // test0<cpp17_output_iterator<int*>, sentinel_wrapper<cpp17_output_iterator<int*>>>();
-  // test0<cpp20_output_iterator<int*>, sentinel_wrapper<cpp20_output_iterator<int*>>>();
-  test0<forward_iterator<int*> >();
-  test0<bidirectional_iterator<int*> >();
-  test0<random_access_iterator<int*> >();
-  test0<contiguous_iterator<int*>>();
-  test0<int*>();
-
-  return true;
-}
-
 template <class Iter, class Sent, std::size_t N>
 constexpr void test_result(std::array<int, N> input, int starting_value, std::array<int, N> const expected) {
   { // (iterator, sentinel) overload
@@ -100,7 +75,10 @@ constexpr void test_result(std::array<int, N> input, int starting_value, std::ar
     assert(std::ranges::equal(input, expected));
   }
 
-  { // (range) overload
+  // The range overload adds the additional constraint that it must be an outputrange
+  // so skip this for the input iterators we test
+  if constexpr (!std::is_same_v<Iter, cpp17_input_iterator<int*>> &&
+                !std::is_same_v<Iter, cpp20_input_iterator<int*>>) { // (range) overload
     auto in_begin = Iter(input.data());
     auto in_end   = Sent(Iter(input.data() + input.size()));
     auto range    = std::ranges::subrange(std::move(in_begin), std::move(in_end));
@@ -117,27 +95,30 @@ constexpr void test_result(std::array<int, N> input, int starting_value, std::ar
   }
 }
 
-constexpr bool test_results() {
-  using Iter = forward_iterator<int*>;
-  using Sent = sentinel_wrapper<Iter>;
-
+template <class Iter, class Sent = sentinel_wrapper<Iter>>
+constexpr void test_results() {
   // Empty
   test_result<Iter, Sent, 0>({}, 0, {});
   // 1-element sequence
   test_result<Iter, Sent, 1>({1}, 0, {0});
   // Longer sequence
   test_result<Iter, Sent, 5>({1, 2, 3, 4, 5}, 0, {0, 1, 2, 3, 4});
+}
 
-  return true;
+void test_results() {
+  test_results<cpp17_input_iterator<int*>>();
+  test_results<cpp20_input_iterator<int*>>();
+  test_results<cpp17_output_iterator<int*>>();
+  test_results<cpp20_output_iterator<int*>>();
+  test_results<forward_iterator<int*>>();
+  test_results<bidirectional_iterator<int*>>();
+  test_results<random_access_iterator<int*>>();
+  test_results<contiguous_iterator<int*>>();
+  test_results<int*>();
 }
 
 int main(int, char**) {
   test_constraints();
-
-  test0();
-  static_assert(test0());
-
   test_results();
-  static_assert(test_results());
   return 0;
 }
\ No newline at end of file

>From ab4c67d3537379aab5117ac8dad232c5072991e9 Mon Sep 17 00:00:00 2001
From: James Smith <james.smith9113 at gmail.com>
Date: Sat, 7 Oct 2023 12:40:02 -0400
Subject: [PATCH 6/6] [libc++] Implement ranges::iota: Using clang-format-17 to
 make CI checks happy

---
 .../numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp   | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
index 611293debbf731b..3a7bc4319bebd6e 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.iota/ranges.iota.pass.cpp
@@ -26,9 +26,8 @@ concept HasIotaIter = requires(Iter&& iter, Sent&& sent, Value&& val) {
 };
 
 template <class Range, class Value = int>
-concept HasIotaRange = requires(Range&& range, Value&& val) {
-  std::ranges::iota(std::forward<Range>(range), std::forward<Value>(val));
-};
+concept HasIotaRange =
+    requires(Range&& range, Value&& val) { std::ranges::iota(std::forward<Range>(range), std::forward<Value>(val)); };
 
 constexpr void test_constraints() {
   // Test constraints of the iterator/sentinel overload



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