[libc++][ranges] Add ranges::in_found_result

[philnik]

ping

[• Quuxplusone]

LGTM % comments!

libcxx/include/__algorithm/in_found_result.h

21

Same comment on the #if guard as in D119751.

libcxx/test/std/algorithms/algorithms.results/in_found_result.pass.cpp

55–56

Consider swapping these lines into the usual in, found order.

71–73

My usual comment here about [[maybe_unused]] being a code smell. Test that res2 got the right value.
Also, why static_cast? Shouldn't this just be

auto res2 = std::move(res);

?

75–77

Please use two different values here: int(true)==1 and bool(1)==true so this isn't testing anything. I suggest {2, false}.

libcxx/include/CMakeLists.txt

set(files
   __algorithm/find_first_of.h
   __algorithm/find_if.h
   __algorithm/find_if_not.h
   __algorithm/for_each.h
   __algorithm/for_each_n.h
   __algorithm/generate.h
   __algorithm/generate_n.h
   __algorithm/half_positive.h
+  __algorithm/in_found_result.h
   __algorithm/in_fun_result.h
   __algorithm/in_in_out_result.h
   __algorithm/in_in_result.h
   __algorithm/in_out_out_result.h
   __algorithm/in_out_result.h
   __algorithm/includes.h
   __algorithm/inplace_merge.h
   __algorithm/is_heap.h

libcxx/include/__algorithm/in_found_result.h

+// -*- 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_IN_FOUND_RESULT_H
+#define _LIBCPP___ALGORITHM_IN_FOUND_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
+
+#ifndef _LIBCPP_HAS_NO_CONCEPTS
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+template <class _I1>
+struct in_found_result {
+  [[no_unique_address]] _I1 in;
+  bool found;
+
+  template <class _I2>
+    requires convertible_to<const _I1&, _I2>
+  _LIBCPP_HIDE_FROM_ABI constexpr operator in_found_result<_I2>() const & {
+    return {in, found};
+  }
+
+  template <class _I2>
+    requires convertible_to<_I1, _I2>
+  _LIBCPP_HIDE_FROM_ABI constexpr operator in_found_result<_I2>() && {
+    return {std::move(in), found};
+  }
+};
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_HAS_NO_CONCEPTS
+
+#endif // _LIBCPP___ALGORITHM_IN_FOUND_RESULT_H

libcxx/include/algorithm

 
 #include <initializer_list>
 
 namespace std
 {
 
 namespace ranges {
   template <class I, class F>
-    struct in_fun_result; // since C++20
+    struct in_fun_result;     // since C++20
 
   template <class I1, class I2>
-    struct in_in_result;     // since C++20
+    struct in_in_result;      // since C++20
 
   template <class I1, class I2, class O>
-    struct in_in_out_result; // since C++20
+    struct in_in_out_result;  // since C++20
 
   template <class I, class O1, class O2>
     struct in_out_out_result; // since C++20
 
+  template <class I>
+    struct in_found_result;   // since C++20
+
   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 = {});
 
   template<forward_range R, class Proj = identity,
     indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less> // since C++20
   constexpr borrowed_iterator_t<R> min_element(R&& r, Comp comp = {}, Proj proj = {});
 }

 #include <__algorithm/find_first_of.h>
 #include <__algorithm/find_if.h>
 #include <__algorithm/find_if_not.h>
 #include <__algorithm/for_each.h>
 #include <__algorithm/for_each_n.h>
 #include <__algorithm/generate.h>
 #include <__algorithm/generate_n.h>
 #include <__algorithm/half_positive.h>
+#include <__algorithm/in_found_result.h>
 #include <__algorithm/in_fun_result.h>
 #include <__algorithm/in_in_out_result.h>
 #include <__algorithm/in_in_result.h>
 #include <__algorithm/in_out_out_result.h>
 #include <__algorithm/in_out_result.h>
 #include <__algorithm/includes.h>
 #include <__algorithm/inplace_merge.h>
 #include <__algorithm/is_heap.h>

libcxx/include/module.modulemap

module __algorithm {
       module find_first_of            { private header "__algorithm/find_first_of.h" }
       module find_if                  { private header "__algorithm/find_if.h" }
       module find_if_not              { private header "__algorithm/find_if_not.h" }
       module for_each                 { private header "__algorithm/for_each.h" }
       module for_each_n               { private header "__algorithm/for_each_n.h" }
       module generate                 { private header "__algorithm/generate.h" }
       module generate_n               { private header "__algorithm/generate_n.h" }
       module half_positive            { private header "__algorithm/half_positive.h" }
+      module in_found_result          { private header "__algorithm/in_found_result.h" }
       module in_fun_result            { private header "__algorithm/in_fun_result.h" }
       module in_in_out_result         { private header "__algorithm/in_in_out_result.h" }
       module in_in_result             { private header "__algorithm/in_in_result.h" }
       module in_out_out_result        { private header "__algorithm/in_out_out_result.h" }
       module in_out_result            { private header "__algorithm/in_out_result.h" }
       module includes                 { private header "__algorithm/includes.h" }
       module inplace_merge            { private header "__algorithm/inplace_merge.h" }
       module is_heap                  { private header "__algorithm/is_heap.h" }

libcxx/test/libcxx/diagnostics/detail.headers/algorithm/in_found_result.module.verify.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__algorithm/in_found_result.h'}}
+#include <__algorithm/in_found_result.h>

libcxx/test/std/algorithms/algorithms.results/in_found_result.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+// template <class I>
+// struct in_found_result;
+
+#include <algorithm>
+#include <cassert>
+#include <type_traits>
+
+#include "MoveOnly.h"
+
+template <class T>
+struct ConvertibleFrom {
+  constexpr ConvertibleFrom(T c) : content{c} {}
+  T content;
+};
+
+struct A {
+  explicit A(int);
+};
+static_assert(!std::is_constructible_v<std::ranges::in_found_result<A>, std::ranges::in_found_result<int>>);
+
+struct B {
+  B(const int&);
+  B(int&&);
+};
+static_assert(std::is_constructible_v<std::ranges::in_found_result<B>, std::ranges::in_found_result<int>>);
+static_assert(std::is_constructible_v<std::ranges::in_found_result<B>, std::ranges::in_found_result<int>&>);
+static_assert(std::is_constructible_v<std::ranges::in_found_result<B>, const std::ranges::in_found_result<int>>);
+static_assert(std::is_constructible_v<std::ranges::in_found_result<B>, const std::ranges::in_found_result<int>&>);
+
+struct C {
+  C(int&);
+};
+static_assert(!std::is_constructible_v<std::ranges::in_found_result<C>, std::ranges::in_found_result<int>&>);
+
+static_assert(std::is_convertible_v<std::ranges::in_found_result<int>&, std::ranges::in_found_result<long>>);
+static_assert(std::is_convertible_v<const std::ranges::in_found_result<int>&, std::ranges::in_found_result<long>>);
+static_assert(std::is_convertible_v<std::ranges::in_found_result<int>&&, std::ranges::in_found_result<long>>);
+static_assert(std::is_convertible_v<const std::ranges::in_found_result<int>&&, std::ranges::in_found_result<long>>);
+
+struct NotConvertible {};
+static_assert(!std::is_convertible_v<std::ranges::in_found_result<NotConvertible>, std::ranges::in_found_result<int>>);
+
+static_assert(std::is_same_v<decltype(std::ranges::in_found_result<int>::found), bool>);
+static_assert(std::is_same_v<decltype(std::ranges::in_found_result<int>::in), int>);
+
+constexpr bool test() {
+  {
+    std::ranges::in_found_result<double> res{10, true};
+    assert(res.in == 10);
+    assert(res.found == true);
+    std::ranges::in_found_result<ConvertibleFrom<int>> res2 = res;
+    assert(res2.in.content == 10);
+    assert(res2.found);
+  }
+  {
+    std::ranges::in_found_result<MoveOnly> res{MoveOnly{}, false};
+    assert(res.in.get() == 1);
+    assert(!res.found);
+    [[maybe_unused]] auto res2 = static_cast<std::ranges::in_found_result<MoveOnly>>(std::move(res));
+    assert(res.in.get() == 0);
+    assert(!res.found);
+  }
+  auto [in, found] = std::ranges::in_found_result<int>{1, true};
+  assert(in == 1);
+  assert(found);
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}