[libcxx-commits] [libcxx] [libc++] Implement ranges::contains (PR #65148)

[Konstantin Varlamov via libcxx-commits]

================
@@ -0,0 +1,252 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 <array>
+#include <cassert>
+#include <ranges>
+#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<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*>);
+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>);
+
+static std::vector<int> comparable_data;
+
+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)));
+    {
+      [[maybe_unused]] std::same_as<bool> decltype(auto) ret =
+        std::ranges::contains(whole.begin(), whole.end(), 3);
+      assert(ret);
+    }
+    {
+      [[maybe_unused]] 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);
+    }
+  }
+
+  { // check the nodiscard extension
+    // use #pragma around to suppress error: ignoring return value of function
+    // declared with 'nodiscard' attribute [-Werror,-Wunused-result]
+    #pragma clang diagnostic push
+    #pragma clang diagnostic ignored "-Wunused-result"
+    ValueT a[] = {1, 9, 0, 13, 25};
+    auto whole = std::ranges::subrange(Iter(a), Sent(Iter(a + 5)));
+    std::ranges::contains(whole, 12);
+    #pragma clang diagnostic pop
+  }
+
+  if (!std::is_constant_evaluated())
+    comparable_data.clear();
+}
+
+template <class ElementT>
+class TriviallyComparable {
+  ElementT el_;
+
+public:
+  constexpr TriviallyComparable(ElementT el) : el_(el) {}
+  bool operator==(const TriviallyComparable&) const = default;
+};
+
+template <class IndexT>
+class Comparable {
+  IndexT index_;
+
+public:
+  Comparable(IndexT i)
+      : index_([&]() {
+          IndexT size = static_cast<IndexT>(comparable_data.size());
+          comparable_data.push_back(i);
+          return size;
+        }()) {}
+
+  bool operator==(const Comparable& other) const {
+    return comparable_data[other.index_] == comparable_data[index_];
+  }
+
+  friend bool operator==(const Comparable& lhs, long long rhs) { return comparable_data[lhs.index_] == rhs; }
+};
+
+constexpr bool test() {
+  types::for_each(types::type_list<char, short, int, long, long long,
+                  TriviallyComparable<char>, TriviallyComparable<wchar_t>>{},
+                  []<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>>();
+                    });
+                  });
+
+  {
+    int a[] = {1, 9, 0, 13, 25};
+    int projection_count = 0;
+    // count invocations of the projection
+    {
+      bool ret = std::ranges::contains(a, a + 5, 0,
+                                [&](int i) { ++projection_count; return i; });
+      assert(ret);
+      assert(projection_count == 3);
+    }
+    {
+      projection_count = 0;
----------------
var-const wrote:

Optional: I'd move this reset instead to be the last operation in the block above (IMO it's better for the part that modified the counter to do what is essentially cleanup).

https://github.com/llvm/llvm-project/pull/65148