[libc++] Implement ranges::contains (#65148)

Differential Revision: https://reviews.llvm.org/D159232
```
Running ./ranges_contains.libcxx.out
Run on (10 X 24.121 MHz CPU s)
CPU Caches:
  L1 Data 64 KiB (x10)
  L1 Instruction 128 KiB (x10)
  L2 Unified 4096 KiB (x5)
Load Average: 3.37, 6.77, 5.27
--------------------------------------------------------------------
Benchmark                          Time             CPU   Iterations
--------------------------------------------------------------------
bm_contains_char/16             1.88 ns         1.87 ns    371607095
bm_contains_char/256            7.48 ns         7.47 ns     93292285
bm_contains_char/4096           99.7 ns         99.6 ns      7013185
bm_contains_char/65536          1296 ns         1294 ns       540436
bm_contains_char/1048576       23887 ns        23860 ns        29302
bm_contains_char/16777216     389420 ns       389095 ns         1796
bm_contains_int/16              7.14 ns         7.14 ns     97776288
bm_contains_int/256             90.4 ns         90.3 ns      7558089
bm_contains_int/4096            1294 ns         1290 ns       543052
bm_contains_int/65536          20482 ns        20443 ns        34334
bm_contains_int/1048576       328817 ns       327965 ns         2147
bm_contains_int/16777216     5246279 ns      5239361 ns          133
bm_contains_bool/16             2.19 ns         2.19 ns    322565780
bm_contains_bool/256            3.42 ns         3.41 ns    205025467
bm_contains_bool/4096           22.1 ns         22.1 ns     31780479
bm_contains_bool/65536           333 ns          332 ns      2106606
bm_contains_bool/1048576        5126 ns         5119 ns       135901
bm_contains_bool/16777216      81656 ns        81574 ns         8569
```

---------

Co-authored-by: Nathan Gauër <brioche@google.com>

libcxx/benchmarks/CMakeLists.txt

@@ -185,6 +185,7 @@ set(BENCHMARK_TESTS
     algorithms/pop_heap.bench.cpp
     algorithms/pstl.stable_sort.bench.cpp
     algorithms/push_heap.bench.cpp
+    algorithms/ranges_contains.bench.cpp
     algorithms/ranges_ends_with.bench.cpp
     algorithms/ranges_make_heap.bench.cpp
     algorithms/ranges_make_heap_then_sort_heap.bench.cpp

libcxx/benchmarks/algorithms/ranges_contains.bench.cpp

@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <algorithm>
+#include <benchmark/benchmark.h>
+#include <iterator>
+#include <vector>
+
+#include "test_iterators.h"
+
+static void bm_contains_char(benchmark::State& state) {
+  std::vector<char> a(state.range(), 'a');
+
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a);
+
+    benchmark::DoNotOptimize(std::ranges::contains(a.begin(), a.end(), 'B'));
+  }
+}
+BENCHMARK(bm_contains_char)->RangeMultiplier(16)->Range(16, 16 << 20);
+
+static void bm_contains_int(benchmark::State& state) {
+  std::vector<int> a(state.range(), 1);
+
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a);
+
+    benchmark::DoNotOptimize(std::ranges::contains(a.begin(), a.end(), 2));
+  }
+}
+BENCHMARK(bm_contains_int)->RangeMultiplier(16)->Range(16, 16 << 20);
+
+static void bm_contains_bool(benchmark::State& state) {
+  std::vector<bool> a(state.range(), true);
+
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(a);
+
+    benchmark::DoNotOptimize(std::ranges::contains(a.begin(), a.end(), false));
+  }
+}
+BENCHMARK(bm_contains_bool)->RangeMultiplier(16)->Range(16, 16 << 20);
+
+BENCHMARK_MAIN();

libcxx/include/CMakeLists.txt

@@ -108,6 +108,7 @@ set(files
   __algorithm/ranges_any_of.h
   __algorithm/ranges_binary_search.h
   __algorithm/ranges_clamp.h
+  __algorithm/ranges_contains.h
   __algorithm/ranges_copy.h
   __algorithm/ranges_copy_backward.h
   __algorithm/ranges_copy_if.h

libcxx/include/__algorithm/ranges_contains.h

@@ -0,0 +1,61 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_CONTAINS_H
+#define _LIBCPP___ALGORITHM_RANGES_CONTAINS_H
+
+#include <__algorithm/ranges_find.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/ranges_operations.h>
+#include <__functional/reference_wrapper.h>
+#include <__iterator/concepts.h>
+#include <__iterator/indirectly_comparable.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER >= 23
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+namespace __contains {
+struct __fn {
+  template <input_iterator _Iter, sentinel_for<_Iter> _Sent, class _Type, class _Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to, projected<_Iter, _Proj>, const _Type*>
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool static
+  operator()(_Iter __first, _Sent __last, const _Type& __value, _Proj __proj = {}) {
+    return ranges::find(std::move(__first), __last, __value, std::ref(__proj)) != __last;
+  }
+
+  template <input_range _Range, class _Type, class _Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Range>, _Proj>, const _Type*>
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool static
+  operator()(_Range&& __range, const _Type& __value, _Proj __proj = {}) {
+    return ranges::find(ranges::begin(__range), ranges::end(__range), __value, std::ref(__proj)) !=
+           ranges::end(__range);
+  }
+};
+} // namespace __contains
+
+inline namespace __cpo {
+inline constexpr auto contains = __contains::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER >= 23
+
+#endif // _LIBCPP___ALGORITHM_RANGES_CONTAINS_H

libcxx/include/__functional/identity.h

@@ -11,6 +11,7 @@
 #define _LIBCPP___FUNCTIONAL_IDENTITY_H
 
 #include <__config>
+#include <__functional/reference_wrapper.h>
 #include <__type_traits/integral_constant.h>
 #include <__utility/forward.h>
 
@@ -34,6 +35,10 @@ struct __identity {
 
 template <>
 struct __is_identity<__identity> : true_type {};
+template <>
+struct __is_identity<reference_wrapper<__identity> > : true_type {};
+template <>
+struct __is_identity<reference_wrapper<const __identity> > : true_type {};
 
 #if _LIBCPP_STD_VER >= 20
 
@@ -48,6 +53,10 @@ struct identity {
 
 template <>
 struct __is_identity<identity> : true_type {};
+template <>
+struct __is_identity<reference_wrapper<identity> > : true_type {};
+template <>
+struct __is_identity<reference_wrapper<const identity> > : true_type {};
 
 #endif // _LIBCPP_STD_VER >= 20
 

libcxx/include/algorithm

@@ -226,6 +226,14 @@ namespace ranges {
   template<class I1, class I2>
     using copy_backward_result = in_out_result<I1, I2>;                                     // since C++20
 
+  template<input_iterator I, sentinel_for<I> S, class T, class Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+    constexpr bool ranges::contains(I first, S last, const T& value, Proj proj = {});       // since C++23
+
+  template<input_range R, class T, class Proj = identity>
+    requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
+    constexpr bool ranges::contains(R&& r, const T& value, Proj proj = {});                 // since C++23
+
   template<input_iterator I, sentinel_for<I> S, weakly_incrementable O>
     requires indirectly_copyable<I, O>
     constexpr ranges::copy_result<I, O> ranges::copy(I first, S last, O result);            // since C++20
@@ -1845,6 +1853,7 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/ranges_any_of.h>
 #include <__algorithm/ranges_binary_search.h>
 #include <__algorithm/ranges_clamp.h>
+#include <__algorithm/ranges_contains.h>
 #include <__algorithm/ranges_copy.h>
 #include <__algorithm/ranges_copy_backward.h>
 #include <__algorithm/ranges_copy_if.h>

libcxx/include/module.modulemap.in

@@ -787,6 +787,7 @@ module std_private_algorithm_ranges_clamp                                [system
   header "__algorithm/ranges_clamp.h"
   export std_private_functional_ranges_operations
 }
+module std_private_algorithm_ranges_contains                             [system] { header "__algorithm/ranges_contains.h" }
 module std_private_algorithm_ranges_copy                                 [system] {
   header "__algorithm/ranges_copy.h"
   export std_private_algorithm_in_out_result

libcxx/modules/std/algorithm.inc

@@ -41,12 +41,12 @@ export namespace std {
   }
 
   // [alg.contains], contains
-#if 0
   namespace ranges {
     using std::ranges::contains;
+#if 0
     using std::ranges::contains_subrange;
-  } // namespace ranges
 #endif
+  } // namespace ranges
 
   // [alg.foreach], for each
   using std::for_each;

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp

@@ -81,6 +81,12 @@ constexpr bool all_the_algorithms()
     (void)std::ranges::binary_search(first, last, value, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::binary_search(a, value, Less(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::clamp(T(), T(), T(), Less(), Proj(&copies)); assert(copies == 0);
+#if TEST_STD_VER >= 23
+    (void)std::ranges::contains(first, last, value, Proj(&copies));
+    assert(copies == 0);
+    (void)std::ranges::contains(a, value, Proj(&copies));
+    assert(copies == 0);
+#endif
     (void)std::ranges::count(first, last, value, Proj(&copies)); assert(copies == 0);
     (void)std::ranges::count(a, value, Proj(&copies)); assert(copies == 0);
     (void)std::ranges::count_if(first, last, UnaryTrue(), Proj(&copies)); assert(copies == 0);

libcxx/test/libcxx/diagnostics/nodiscard_extensions.compile.pass.cpp

@@ -45,6 +45,9 @@ void test_algorithms() {
 #if TEST_STD_VER >= 17
   std::clamp(2, 1, 3);
   std::clamp(2, 3, 1, std::greater<int>());
+#endif
+#if TEST_STD_VER >= 23
+  std::ranges::contains(arr, arr + 1, 1);
 #endif
   std::count_if(std::begin(arr), std::end(arr), P());
   std::count(std::begin(arr), std::end(arr), 1);

libcxx/test/libcxx/diagnostics/nodiscard_extensions.verify.cpp

@@ -60,6 +60,11 @@ void test_algorithms() {
   std::clamp(2, 1, 3, std::greater<int>());
 #endif
 
+#if TEST_STD_VER >= 23
+  // expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::ranges::contains(arr, arr + 1, 1);
+#endif
+
   // expected-warning@+1 {{ignoring return value of function declared with 'nodiscard' attribute}}
   std::count_if(std::begin(arr), std::end(arr), P());
 

libcxx/test/std/algorithms/alg.nonmodifying/alg.contains/ranges.contains.pass.cpp

@@ -0,0 +1,298 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// template<input_iterator I, sentinel_for<I> S, class T, class Proj = identity>
+//     requires indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+//     constexpr bool ranges::contains(I first, S last, const T& value, Proj proj = {});       // since C++23
+
+// template<input_range R, class T, class Proj = identity>
+//     requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
+//     constexpr bool ranges::contains(R&& r, const T& value, Proj proj = {});                 // since C++23
+
+#include <algorithm>
+#include <cassert>
+#include <list>
+#include <ranges>
+#include <string>
+#include <vector>
+
+#include "almost_satisfies_types.h"
+#include "boolean_testable.h"
+#include "test_iterators.h"
+
+struct NotEqualityComparable {};
+
+template <class Iter, class Sent = Iter>
+concept HasContainsIt = requires(Iter iter, Sent sent) { std::ranges::contains(iter, sent, *iter); };
+
+static_assert(HasContainsIt<int*>);
+static_assert(HasContainsIt<int*, int*>);
+static_assert(!HasContainsIt<NotEqualityComparable*>);
+static_assert(!HasContainsIt<InputIteratorNotDerivedFrom>);
+static_assert(!HasContainsIt<InputIteratorNotIndirectlyReadable>);
+static_assert(!HasContainsIt<InputIteratorNotInputOrOutputIterator>);
+static_assert(!HasContainsIt<cpp20_input_iterator<int*>, SentinelForNotSemiregular>);
+static_assert(!HasContainsIt<cpp20_input_iterator<int*>, InputRangeNotSentinelEqualityComparableWith>);
+static_assert(!HasContainsIt<cpp20_input_iterator<int*>, sentinel_wrapper<cpp20_input_iterator<int*>>>);
+
+static_assert(!HasContainsIt<int*, int>);
+static_assert(!HasContainsIt<int, int*>);
+
+template <class Range, class ValT>
+concept HasContainsR = requires(Range&& range) { std::ranges::contains(std::forward<Range>(range), ValT{}); };
+
+static_assert(!HasContainsR<int, int>);
+static_assert(HasContainsR<int[1], int>);
+static_assert(!HasContainsR<NotEqualityComparable[1], NotEqualityComparable>);
+static_assert(!HasContainsR<InputRangeNotDerivedFrom, int>);
+static_assert(!HasContainsR<InputRangeNotIndirectlyReadable, int>);
+static_assert(!HasContainsR<InputRangeNotInputOrOutputIterator, int>);
+static_assert(!HasContainsR<InputRangeNotSentinelSemiregular, int>);
+static_assert(!HasContainsR<InputRangeNotSentinelEqualityComparableWith, int>);
+
+template <class Iter, class Sent = Iter>
+constexpr void test_iterators() {
+  using ValueT = std::iter_value_t<Iter>;
+  { // simple tests
+    ValueT a[] = {1, 2, 3, 4, 5, 6};
+    auto whole = std::ranges::subrange(Iter(a), Sent(Iter(a + 6)));
+    {
+      std::same_as<bool> decltype(auto) ret = std::ranges::contains(whole.begin(), whole.end(), 3);
+      assert(ret);
+    }
+    {
+      std::same_as<bool> decltype(auto) ret = std::ranges::contains(whole, 3);
+      assert(ret);
+    }
+  }
+
+  { // check that a range with a single element works
+    ValueT a[] = {32};
+    auto whole = std::ranges::subrange(Iter(a), Sent(Iter(a + 1)));
+    {
+      bool ret = std::ranges::contains(whole.begin(), whole.end(), 32);
+      assert(ret);
+    }
+    {
+      bool ret = std::ranges::contains(whole, 32);
+      assert(ret);
+    }
+  }
+
+  { // check that an empty range works
+    ValueT a[] = {};
+    auto whole = std::ranges::subrange(Iter(a), Sent(Iter(a)));
+    {
+      bool ret = std::ranges::contains(whole.begin(), whole.end(), 1);
+      assert(!ret);
+    }
+    {
+      bool ret = std::ranges::contains(whole, 1);
+      assert(!ret);
+    }
+  }
+
+  { // check that the first element matches
+    ValueT a[] = {32, 3, 2, 1, 0, 23, 21, 9, 40, 100};
+    auto whole = std::ranges::subrange(Iter(a), Sent(Iter(a + 10)));
+    {
+      bool ret = std::ranges::contains(whole.begin(), whole.end(), 32);
+      assert(ret);
+    }
+    {
+      bool ret = std::ranges::contains(whole, 32);
+      assert(ret);
+    }
+  }
+
+  { // check that the last element matches
+    ValueT a[] = {3, 22, 1, 43, 99, 0, 56, 100, 32};
+    auto whole = std::ranges::subrange(Iter(a), Sent(Iter(a + 9)));
+    {
+      bool ret = std::ranges::contains(whole.begin(), whole.end(), 32);
+      assert(ret);
+    }
+    {
+      bool ret = std::ranges::contains(whole, 32);
+      assert(ret);
+    }
+  }
+
+  { // no match
+    ValueT a[] = {13, 1, 21, 4, 5};
+    auto whole = std::ranges::subrange(Iter(a), Sent(Iter(a + 5)));
+    {
+      bool ret = std::ranges::contains(whole.begin(), whole.end(), 10);
+      assert(!ret);
+    }
+    {
+      bool ret = std::ranges::contains(whole, 10);
+      assert(!ret);
+    }
+  }
+
+  { // check that the projections are used
+    int a[] = {1, 9, 0, 13, 25};
+    {
+      bool ret = std::ranges::contains(a, a + 5, -13, [&](int i) { return i * -1; });
+      assert(ret);
+    }
+    {
+      auto range = std::ranges::subrange(a, a + 5);
+      bool ret   = std::ranges::contains(range, -13, [&](int i) { return i * -1; });
+      assert(ret);
+    }
+  }
+}
+
+constexpr bool test() {
+  types::for_each(types::type_list<char, long long>{}, []<class T> {
+    types::for_each(types::cpp20_input_iterator_list<T*>{}, []<class Iter> {
+      if constexpr (std::forward_iterator<Iter>)
+        test_iterators<Iter>();
+      test_iterators<Iter, sentinel_wrapper<Iter>>();
+      test_iterators<Iter, sized_sentinel<Iter>>();
+    });
+  });
+
+  { // count invocations of the projection for continuous iterators
+    int a[]              = {1, 9, 0, 13, 25};
+    int projection_count = 0;
+    {
+      bool ret = std::ranges::contains(a, a + 5, 0, [&](int i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 3);
+      projection_count = 0;
+    }
+    {
+      bool ret = std::ranges::contains(a, 0, [&](int i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 3);
+    }
+  }
+
+  { // check invocations of the projection for std::string
+    const std::string str{"hello world"};
+    const std::string str1{"hi world"};
+    int projection_count = 0;
+    {
+      std::string a[] = {str1, str1, str, str1, str1};
+      auto whole =
+          std::ranges::subrange(forward_iterator(std::move_iterator(a)), forward_iterator(std::move_iterator(a + 5)));
+      bool ret = std::ranges::contains(whole.begin(), whole.end(), "hello world", [&](const std::string i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 3);
+      projection_count = 0;
+    }
+    {
+      std::string a[] = {str1, str1, str, str1, str1};
+      auto whole =
+          std::ranges::subrange(forward_iterator(std::move_iterator(a)), forward_iterator(std::move_iterator(a + 5)));
+      bool ret = std::ranges::contains(whole, "hello world", [&](const std::string i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 3);
+    }
+  }
+
+  { // check invocations of the projection for non-continuous iterators
+    std::vector<bool> whole{false, false, true, false};
+    int projection_count = 0;
+    {
+      bool ret = std::ranges::contains(whole.begin(), whole.end(), true, [&](int i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 3);
+      projection_count = 0;
+    }
+    {
+      bool ret = std::ranges::contains(whole, true, [&](int i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 3);
+    }
+  }
+
+  { // check invocations of the projection for views::transform
+    int a[]              = {1, 2, 3, 4, 5};
+    int projection_count = 0;
+    auto square_number   = a | std::views::transform([](int x) { return x * x; });
+    {
+      bool ret = std::ranges::contains(square_number.begin(), square_number.end(), 16, [&](int i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 4);
+      projection_count = 0;
+    }
+    {
+      bool ret = std::ranges::contains(square_number, 16, [&](int i) {
+        ++projection_count;
+        return i;
+      });
+      assert(ret);
+      assert(projection_count == 4);
+    }
+  }
+
+  return true;
+}
+
+// test for non-contiguous containers
+bool test_nonconstexpr() {
+  std::list<int> a     = {7, 5, 0, 16, 8};
+  int projection_count = 0;
+  {
+    bool ret = std::ranges::contains(a.begin(), a.end(), 0, [&](int i) {
+      ++projection_count;
+      return i;
+    });
+    assert(ret);
+    assert(projection_count == 3);
+    projection_count = 0;
+  }
+  {
+    bool ret = std::ranges::contains(a, 0, [&](int i) {
+      ++projection_count;
+      return i;
+    });
+    assert(ret);
+    assert(projection_count == 3);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  assert(test_nonconstexpr());
+
+  return 0;
+}

libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp

@@ -75,6 +75,7 @@ constexpr bool test_all() {
   test(std::ranges::any_of, in, &Foo::unary_pred, &Bar::val);
   test(std::ranges::all_of, in, &Foo::unary_pred, &Bar::val);
 #if TEST_STD_VER >= 23
+  test(std::ranges::contains, in, x, &Bar::val);
   test(std::ranges::ends_with, in, in2, &Foo::binary_pred, &Bar::val, &Bar::val);
 #endif
   test(std::ranges::none_of, in, &Foo::unary_pred, &Bar::val);

libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp

@@ -75,6 +75,7 @@ constexpr void run_tests() {
   test(std::ranges::any_of, in, unary_pred);
   test(std::ranges::all_of, in, unary_pred);
 #if TEST_STD_VER >= 23
+  test(std::ranges::contains, in, x);
   test(std::ranges::ends_with, in, in2);
 #endif
   test(std::ranges::none_of, in, unary_pred);

libcxx/test/std/library/description/conventions/customization.point.object/niebloid.compile.pass.cpp

@@ -65,6 +65,9 @@ static_assert(test(std::ranges::all_of, a, odd));
 static_assert(test(std::ranges::any_of, a, odd));
 static_assert(test(std::ranges::binary_search, a, 42));
 static_assert(test(std::ranges::clamp, 42, 42, 42));
+#if TEST_STD_VER >= 23
+static_assert(test(std::ranges::contains, a, 42));
+#endif
 static_assert(test(std::ranges::copy, a, a));
 static_assert(test(std::ranges::copy_backward, a, a));
 static_assert(test(std::ranges::copy_if, a, a, odd));