[libc++][ranges] Add ranges::min_max_result

[philnik]

Rebased

[• Quuxplusone]

Assuming there's nothing subtly surprising in the test file, LGTM!

libcxx/include/__algorithm/min_max_result.h

27

and likewise adjust the #endif comment. (Also, FYI, going forward it will help to use the form #if !defined(_LIBCPP_HAS_NO_CONCEPTS) consistently, instead of #ifndef, because greppability.)

(This is basically a merge conflict with D118736. Going forward, we should guard everything new in the ranges namespace with _LIBCPP_HAS_NO_INCOMPLETE_RANGES, unless it's a building block for something in the std:: namespace, and until we are ready to kill off _LIBCPP_HAS_NO_INCOMPLETE_RANGES entirely, which will be a while.)

libcxx/include/algorithm

23

Either space-align this comment too, or don't bother aligning comments? (I don't really care about the alignment personally. Seems like it just adds to the git blame spam.)

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

73–75

s/in1/min/g
s/in2/max/g

libcxx/include/CMakeLists.txt

set(files
   __algorithm/lexicographical_compare.h
   __algorithm/lower_bound.h
   __algorithm/make_heap.h
   __algorithm/max.h
   __algorithm/max_element.h
   __algorithm/merge.h
   __algorithm/min.h
   __algorithm/min_element.h
+  __algorithm/min_max_result.h
   __algorithm/minmax.h
   __algorithm/minmax_element.h
   __algorithm/mismatch.h
   __algorithm/move.h
   __algorithm/move_backward.h
   __algorithm/next_permutation.h
   __algorithm/none_of.h
   __algorithm/nth_element.h

libcxx/include/__algorithm/min_max_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_MIN_MAX_RESULT_H
+#define _LIBCPP___ALGORITHM_MIN_MAX_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!defined(_LIBCPP_HAS_NO_CONCEPTS) && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+namespace ranges {
+
+template <class _T1>
+struct min_max_result {
+  [[no_unique_address]] _T1 min;
+  [[no_unique_address]] _T1 max;
+
+  template <class _T2>
+    requires convertible_to<const _T1&, _T2>
+  _LIBCPP_HIDE_FROM_ABI constexpr operator min_max_result<_T2>() const & {
+    return {min, max};
+  }
+
+  template <class _T2>
+    requires convertible_to<_T1, _T2>
+  _LIBCPP_HIDE_FROM_ABI constexpr operator min_max_result<_T2>() && {
+    return {std::move(min), std::move(max)};
+  }
+};
+
+} // namespace ranges
+
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif

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 I1, class I2>
+    struct min_max_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/lexicographical_compare.h>
 #include <__algorithm/lower_bound.h>
 #include <__algorithm/make_heap.h>
 #include <__algorithm/max.h>
 #include <__algorithm/max_element.h>
 #include <__algorithm/merge.h>
 #include <__algorithm/min.h>
 #include <__algorithm/min_element.h>
+#include <__algorithm/min_max_result.h>
 #include <__algorithm/minmax.h>
 #include <__algorithm/minmax_element.h>
 #include <__algorithm/mismatch.h>
 #include <__algorithm/move.h>
 #include <__algorithm/move_backward.h>
 #include <__algorithm/next_permutation.h>
 #include <__algorithm/none_of.h>
 #include <__algorithm/nth_element.h>

libcxx/include/module.modulemap

module __algorithm {
       module lexicographical_compare  { private header "__algorithm/lexicographical_compare.h" }
       module lower_bound              { private header "__algorithm/lower_bound.h" }
       module make_heap                { private header "__algorithm/make_heap.h" }
       module max                      { private header "__algorithm/max.h" }
       module max_element              { private header "__algorithm/max_element.h" }
       module merge                    { private header "__algorithm/merge.h" }
       module min                      { private header "__algorithm/min.h" }
       module min_element              { private header "__algorithm/min_element.h" }
+      module min_max_result           { private header "__algorithm/min_max_result.h" }
       module minmax                   { private header "__algorithm/minmax.h" }
       module minmax_element           { private header "__algorithm/minmax_element.h" }
       module mismatch                 { private header "__algorithm/mismatch.h" }
       module move                     { private header "__algorithm/move.h" }
       module move_backward            { private header "__algorithm/move_backward.h" }
       module next_permutation         { private header "__algorithm/next_permutation.h" }
       module none_of                  { private header "__algorithm/none_of.h" }
       module nth_element              { private header "__algorithm/nth_element.h" }

libcxx/test/libcxx/diagnostics/detail.headers/algorithm/min_max_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/min_max_result.h'}}
+#include <__algorithm/min_max_result.h>

libcxx/test/std/algorithms/algorithms.results/min_max_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 I1, class I2>
+// struct min_max_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::min_max_result<A>, std::ranges::min_max_result<int>>);
+
+struct B {
+  B(const int&);
+  B(int&&);
+};
+static_assert(std::is_constructible_v<std::ranges::min_max_result<B>, std::ranges::min_max_result<int>>);
+static_assert(std::is_constructible_v<std::ranges::min_max_result<B>, std::ranges::min_max_result<int>&>);
+static_assert(std::is_constructible_v<std::ranges::min_max_result<B>, const std::ranges::min_max_result<int>>);
+static_assert(std::is_constructible_v<std::ranges::min_max_result<B>, const std::ranges::min_max_result<int>&>);
+
+struct C {
+  C(int&);
+};
+static_assert(!std::is_constructible_v<std::ranges::min_max_result<C>, std::ranges::min_max_result<int>&>);
+
+static_assert(std::is_convertible_v<std::ranges::min_max_result<int>&, std::ranges::min_max_result<long>>);
+static_assert(std::is_convertible_v<const std::ranges::min_max_result<int>&, std::ranges::min_max_result<long>>);
+static_assert(std::is_convertible_v<std::ranges::min_max_result<int>&&, std::ranges::min_max_result<long>>);
+static_assert(std::is_convertible_v<const std::ranges::min_max_result<int>&&, std::ranges::min_max_result<long>>);
+
+struct NotConvertible {};
+static_assert(!std::is_convertible_v<std::ranges::min_max_result<NotConvertible>, std::ranges::min_max_result<int>>);
+
+constexpr bool test() {
+  {
+    std::ranges::min_max_result<double> res{10, 1};
+    assert(res.min == 10);
+    assert(res.max == 1);
+    std::ranges::min_max_result<ConvertibleFrom<int>> res2 = res;
+    assert(res2.min.content == 10);
+    assert(res2.max.content == 1);
+  }
+  {
+    std::ranges::min_max_result<MoveOnly> res{MoveOnly{}, MoveOnly{}};
+    assert(res.min.get() == 1);
+    assert(res.max.get() == 1);
+    [[maybe_unused]] auto res2 = static_cast<std::ranges::min_max_result<MoveOnly>>(std::move(res));
+    assert(res.min.get() == 0);
+    assert(res.max.get() == 0);
+  }
+  auto [min, max] = std::ranges::min_max_result<int>{1, 2};
+  assert(min == 1);
+  assert(max == 2);
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}