[libc++] Implement ranges::adjacent_find

Reviewed By: Mordante, var-const, #libc

Spies: libcxx-commits, mgorny

Differential Revision: https://reviews.llvm.org/D126610

libcxx/include/CMakeLists.txt

@@ -66,6 +66,7 @@ set(files
   __algorithm/pop_heap.h
   __algorithm/prev_permutation.h
   __algorithm/push_heap.h
+  __algorithm/ranges_adjacent_find.h
   __algorithm/ranges_all_of.h
   __algorithm/ranges_any_of.h
   __algorithm/ranges_binary_search.h

libcxx/include/__algorithm/ranges_adjacent_find.h

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_ADJACENT_FIND_H
+#define _LIBCPP___ALGORITHM_RANGES_ADJACENT_FIND_H
+
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+namespace __adjacent_find {
+struct __fn {
+
+  template <class _Iter, class _Sent, class _Proj, class _Pred>
+  _LIBCPP_HIDE_FROM_ABI constexpr static
+  _Iter __adjacent_find_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
+    if (__first == __last)
+      return __first;
+
+    auto __i = __first;
+    while (++__i != __last) {
+      if (std::invoke(__pred, std::invoke(__proj, *__first), std::invoke(__proj, *__i)))
+        return __first;
+      __first = __i;
+    }
+    return __i;
+  }
+
+  template <forward_iterator _Iter, sentinel_for<_Iter> _Sent,
+            class _Proj = identity,
+            indirect_binary_predicate<projected<_Iter, _Proj>, projected<_Iter, _Proj>> _Pred = ranges::equal_to>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  _Iter operator()(_Iter __first, _Sent __last, _Pred __pred = {}, _Proj __proj = {}) const {
+    return __adjacent_find_impl(std::move(__first), std::move(__last), __pred, __proj);
+  }
+
+  template <forward_range _Range,
+            class _Proj = identity,
+            indirect_binary_predicate<projected<iterator_t<_Range>, _Proj>,
+                                      projected<iterator_t<_Range>, _Proj>> _Pred = ranges::equal_to>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  borrowed_iterator_t<_Range> operator()(_Range&& __range, _Pred __pred = {}, _Proj __proj = {}) const {
+    return __adjacent_find_impl(ranges::begin(__range), ranges::end(__range), __pred, __proj);
+  }
+};
+} // namespace __adjacent_find
+
+inline namespace __cpo {
+  inline constexpr auto adjacent_find = __adjacent_find::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+#endif // _LIBCPP___ALGORITHM_RANGES_ADJACENT_FIND_H

libcxx/include/algorithm

@@ -391,6 +391,16 @@ namespace ranges {
                             Pred pred = {},
                             Proj1 proj1 = {}, Proj2 proj2 = {});                            // since C++20
 
+  template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
+           indirect_binary_predicate<projected<I, Proj>,
+                                     projected<I, Proj>> Pred = ranges::equal_to>
+    constexpr I ranges::adjacent_find(I first, S last, Pred pred = {}, Proj proj = {});     // since C+20
+
+  template<forward_range R, class Proj = identity,
+           indirect_binary_predicate<projected<iterator_t<R>, Proj>,
+                                     projected<iterator_t<R>, Proj>> Pred = ranges::equal_to>
+    constexpr borrowed_iterator_t<R> ranges::adjacent_find(R&& r, Pred pred = {}, Proj proj = {});  // since C++20
+
 }
 
     constexpr bool     // constexpr in C++20
@@ -1107,6 +1117,7 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/pop_heap.h>
 #include <__algorithm/prev_permutation.h>
 #include <__algorithm/push_heap.h>
+#include <__algorithm/ranges_adjacent_find.h>
 #include <__algorithm/ranges_all_of.h>
 #include <__algorithm/ranges_any_of.h>
 #include <__algorithm/ranges_binary_search.h>

libcxx/include/module.modulemap

@@ -298,6 +298,7 @@ module std [system] {
       module pop_heap                 { private header "__algorithm/pop_heap.h" }
       module prev_permutation         { private header "__algorithm/prev_permutation.h" }
       module push_heap                { private header "__algorithm/push_heap.h" }
+      module ranges_adjacent_find     { private header "__algorithm/ranges_adjacent_find.h" }
       module ranges_all_of            { private header "__algorithm/ranges_all_of.h" }
       module ranges_any_of            { private header "__algorithm/ranges_any_of.h" }
       module ranges_binary_search     { private header "__algorithm/ranges_binary_search.h" }

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp

@@ -90,8 +90,8 @@ constexpr bool all_the_algorithms()
     int count = 1;
 
     int copies = 0;
-    //(void)std::ranges::adjacent_find(first, last, Equal(&copies)); assert(copies == 0);
-    //(void)std::ranges::adjacent_find(a, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::adjacent_find(first, last, Equal(&copies)); assert(copies == 0);
+    (void)std::ranges::adjacent_find(a, Equal(&copies)); assert(copies == 0);
     (void)std::ranges::all_of(first, last, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::all_of(a, UnaryTrue(&copies)); assert(copies == 0);
     (void)std::ranges::any_of(first, last, UnaryTrue(&copies)); assert(copies == 0);

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

@@ -72,8 +72,8 @@ constexpr bool all_the_algorithms()
     int count = 1;
 
     int copies = 0;
-    //(void)std::ranges::adjacent_find(first, last, Equal(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::adjacent_find(a, Equal(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::adjacent_find(first, last, Equal(), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::adjacent_find(a, Equal(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::all_of(first, last, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::all_of(a, UnaryTrue(), Proj(&copies)); assert(copies == 0);
     (void)std::ranges::any_of(first, last, UnaryTrue(), Proj(&copies)); assert(copies == 0);

libcxx/test/libcxx/private_headers.verify.cpp

@@ -103,6 +103,7 @@ END-SCRIPT
 #include <__algorithm/pop_heap.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/pop_heap.h'}}
 #include <__algorithm/prev_permutation.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/prev_permutation.h'}}
 #include <__algorithm/push_heap.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/push_heap.h'}}
+#include <__algorithm/ranges_adjacent_find.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_adjacent_find.h'}}
 #include <__algorithm/ranges_all_of.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_all_of.h'}}
 #include <__algorithm/ranges_any_of.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_any_of.h'}}
 #include <__algorithm/ranges_binary_search.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_binary_search.h'}}

libcxx/test/std/algorithms/alg.nonmodifying/alg.adjacent.find/ranges.adjacent_find.pass.cpp

@@ -0,0 +1,197 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+// template<forward_iterator I, sentinel_for<I> S, class Proj = identity,
+//          indirect_binary_predicate<projected<I, Proj>,
+//                                    projected<I, Proj>> Pred = ranges::equal_to>
+//   constexpr I ranges::adjacent_find(I first, S last, Pred pred = {}, Proj proj = {});
+// template<forward_range R, class Proj = identity,
+//          indirect_binary_predicate<projected<iterator_t<R>, Proj>,
+//                                    projected<iterator_t<R>, Proj>> Pred = ranges::equal_to>
+//   constexpr borrowed_iterator_t<R> ranges::adjacent_find(R&& r, Pred pred = {}, Proj proj = {});
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <cstddef>
+#include <ranges>
+
+#include "almost_satisfies_types.h"
+#include "boolean_testable.h"
+#include "test_iterators.h"
+
+template <class Iter, class Sent = Iter>
+concept HasAdjacentFindIt = requires (Iter iter, Sent sent) { std::ranges::adjacent_find(iter, sent); };
+
+struct NotComparable {};
+
+static_assert(HasAdjacentFindIt<int*>);
+static_assert(!HasAdjacentFindIt<ForwardIteratorNotDerivedFrom>);
+static_assert(!HasAdjacentFindIt<ForwardIteratorNotIncrementable>);
+static_assert(!HasAdjacentFindIt<int*, SentinelForNotSemiregular>);
+static_assert(!HasAdjacentFindIt<int*, SentinelForNotWeaklyEqualityComparableWith>);
+static_assert(!HasAdjacentFindIt<NotComparable*>);
+
+template <class Range>
+concept HasAdjacentFindR = requires (Range range) { std::ranges::adjacent_find(range); };
+
+static_assert(HasAdjacentFindR<UncheckedRange<int*>>);
+static_assert(!HasAdjacentFindR<ForwardRangeNotDerivedFrom>);
+static_assert(!HasAdjacentFindR<ForwardRangeNotIncrementable>);
+static_assert(!HasAdjacentFindR<ForwardRangeNotSentinelSemiregular>);
+static_assert(!HasAdjacentFindR<ForwardRangeNotSentinelEqualityComparableWith>);
+static_assert(!HasAdjacentFindR<UncheckedRange<NotComparable>>);
+
+template <size_t N>
+struct Data {
+  std::array<int, N> input;
+  int expected;
+};
+
+template <class Iter, class Sent, size_t N>
+constexpr void test(Data<N> d) {
+  {
+    std::same_as<Iter> decltype(auto) ret =
+        std::ranges::adjacent_find(Iter(d.input.data()), Sent(Iter(d.input.data() + d.input.size())));
+    assert(base(ret) == d.input.data() + d.expected);
+  }
+  {
+    auto range = std::ranges::subrange(Iter(d.input.data()), Sent(Iter(d.input.data() + d.input.size())));
+    std::same_as<Iter> decltype(auto) ret = std::ranges::adjacent_find(range);
+    assert(base(ret) == d.input.data() + d.expected);
+  }
+}
+
+template <class Iter, class Sent = Iter>
+constexpr void test_iterators() {
+  // simple test
+  test<Iter, Sent, 4>({.input = {1, 2, 2, 4}, .expected = 1});
+  // last is returned with no match
+  test<Iter, Sent, 4>({.input = {1, 2, 3, 4}, .expected = 4});
+  // first elements match
+  test<Iter, Sent, 4>({.input = {1, 1, 3, 4}, .expected = 0});
+  // the first match is returned
+  test<Iter, Sent, 7>({.input = {1, 1, 3, 4, 4, 4, 4}, .expected = 0});
+  // two element range works
+  test<Iter, Sent, 2>({.input = {3, 3}, .expected = 0});
+  // single element range works
+  test<Iter, Sent, 1>({.input = {1}, .expected = 1});
+  // empty range works
+  test<Iter, Sent, 0>({.input = {}, .expected = 0});
+}
+
+constexpr bool test() {
+  test_iterators<forward_iterator<int*>, sentinel_wrapper<forward_iterator<int*>>>();
+  test_iterators<forward_iterator<int*>>();
+  test_iterators<bidirectional_iterator<int*>>();
+  test_iterators<random_access_iterator<int*>>();
+  test_iterators<contiguous_iterator<int*>>();
+  test_iterators<int*>();
+  test_iterators<const int*>();
+
+  { // check that ranges::dangling is returned
+    [[maybe_unused]] std::same_as<std::ranges::dangling> decltype(auto) ret =
+        std::ranges::adjacent_find(std::array{1, 2, 3, 4});
+  }
+
+  { // check that the complexity requirements are met with no match
+    {
+      int predicateCount = 0;
+      auto pred = [&](int, int) { ++predicateCount; return false; };
+      auto projectionCount = 0;
+      auto proj = [&](int i) { ++projectionCount; return i; };
+      int a[] = {1, 2, 3, 4, 5};
+      auto ret = std::ranges::adjacent_find(a, a + 5, pred, proj);
+      assert(ret == a + 5);
+      assert(predicateCount == 4);
+      assert(projectionCount == 8);
+    }
+    {
+      int predicateCount = 0;
+      auto pred = [&](int, int) { ++predicateCount; return false; };
+      auto projectionCount = 0;
+      auto proj = [&](int i) { ++projectionCount; return i; };
+      int a[] = {1, 2, 3, 4, 5};
+      auto ret = std::ranges::adjacent_find(a, pred, proj);
+      assert(ret == a + 5);
+      assert(predicateCount == 4);
+      assert(projectionCount == 8);
+    }
+  }
+
+  { // check that the complexity requirements are met with a match
+    {
+      int predicateCount = 0;
+      auto pred = [&](int i, int j) { ++predicateCount; return i == j; };
+      auto projectionCount = 0;
+      auto proj = [&](int i) { ++projectionCount; return i; };
+      int a[] = {1, 2, 4, 4, 5};
+      auto ret = std::ranges::adjacent_find(a, a + 5, pred, proj);
+      assert(ret == a + 2);
+      assert(predicateCount == 3);
+      assert(projectionCount == 6);
+    }
+    {
+      int predicateCount = 0;
+      auto pred = [&](int i, int j) { ++predicateCount; return i == j; };
+      auto projectionCount = 0;
+      auto proj = [&](int i) { ++projectionCount; return i; };
+      int a[] = {1, 2, 4, 4, 5};
+      auto ret = std::ranges::adjacent_find(a, pred, proj);
+      assert(ret == a + 2);
+      assert(predicateCount == 3);
+      assert(projectionCount == 6);
+    }
+  }
+
+  { // check that std::invoke is used
+    struct S {
+      constexpr S(int i_) : i(i_) {}
+      constexpr bool compare(const S& j) const { return j.i == i; }
+      constexpr const S& identity() const { return *this; }
+      int i;
+    };
+    {
+      S a[] = {1, 2, 3, 4};
+      auto ret = std::ranges::adjacent_find(std::begin(a), std::end(a), &S::compare, &S::identity);
+      assert(ret == a + 4);
+    }
+    {
+      S a[] = {1, 2, 3, 4};
+      auto ret = std::ranges::adjacent_find(a, &S::compare, &S::identity);
+      assert(ret == a + 4);
+    }
+  }
+
+  { // check that the implicit conversion to bool works
+    {
+      int a[] = {1, 2, 2, 4};
+      auto ret = std::ranges::adjacent_find(a, a + 4, [](int i, int j) { return BooleanTestable{i == j}; });
+      assert(ret == a + 1);
+    }
+    {
+      int a[] = {1, 2, 2, 4};
+      auto ret = std::ranges::adjacent_find(a, [](int i, int j) { return BooleanTestable{i == j}; });
+      assert(ret == a + 1);
+    }
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}

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

@@ -60,7 +60,7 @@ auto triple = [](int x) { return 3*x; };
 
 // [algorithm.syn]
 
-//static_assert(test(std::ranges::adjacent_find, a));
+static_assert(test(std::ranges::adjacent_find, a));
 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));