[libcxx-commits] [libcxx] [libc++][ranges] P1223R5: `find_last` (PR #99312)

[nicole mazzuca via libcxx-commits]

================
@@ -0,0 +1,294 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// ADDITIONAL_COMPILE_FLAGS(gcc-style-warnings): -Wno-sign-compare
+// MSVC warning C4242: 'argument': conversion from 'const _Ty' to 'ElementT', possible loss of data
+// MSVC warning C4244: 'argument': conversion from 'const _Ty' to 'ElementT', possible loss of data
+// ADDITIONAL_COMPILE_FLAGS(cl-style-warnings): /wd4242 /wd4244
+
+// template<forward_iterator I, sentinel_for<I> S, class T, class Proj = identity>
+//   requires indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+//   constexpr subrange<I> ranges::find_last(I first, S last, const T& value, Proj proj = {});
+// template<forward_range R, class T, class Proj = identity>
+//   requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
+//   constexpr borrowed_subrange_t<R> ranges::find_last(R&& r, const T& value, Proj proj = {});
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <deque>
+#include <ranges>
+#include <vector>
+
+#include "almost_satisfies_types.h"
+#include "test_iterators.h"
+
+struct NotEqualityComparable {};
+
+template <class It, class Sent = It>
+concept HasFindLastIt = requires(It it, Sent sent) { std::ranges::find_last(it, sent, *it); };
+static_assert(HasFindLastIt<int*>);
+static_assert(HasFindLastIt<forward_iterator<int*>>);
+static_assert(!HasFindLastIt<cpp20_input_iterator<int*>>);
+static_assert(!HasFindLastIt<NotEqualityComparable*>);
+static_assert(!HasFindLastIt<ForwardIteratorNotDerivedFrom>);
+static_assert(!HasFindLastIt<ForwardIteratorNotIncrementable>);
+static_assert(!HasFindLastIt<forward_iterator<int*>, SentinelForNotSemiregular>);
+static_assert(!HasFindLastIt<forward_iterator<int*>, InputRangeNotSentinelEqualityComparableWith>);
+
+static_assert(!HasFindLastIt<int*, int>);
+static_assert(!HasFindLastIt<int, int*>);
+
+template <class Range, class ValT>
+concept HasFindLastR = requires(Range r) { std::ranges::find_last(r, ValT{}); };
+static_assert(HasFindLastR<std::array<int, 1>, int>);
+static_assert(!HasFindLastR<int, int>);
+static_assert(!HasFindLastR<std::array<NotEqualityComparable, 1>, NotEqualityComparable>);
+static_assert(!HasFindLastR<ForwardRangeNotDerivedFrom, int>);
+static_assert(!HasFindLastR<ForwardRangeNotIncrementable, int>);
+static_assert(!HasFindLastR<ForwardRangeNotSentinelSemiregular, int>);
+static_assert(!HasFindLastR<ForwardRangeNotSentinelEqualityComparableWith, int>);
+
+static std::vector<int> comparable_data;
+
+template <class It, class Sent = It>
+constexpr void test_iterators() {
+  using ValueT = std::iter_value_t<It>;
+  { // simple test
+    {
+      ValueT a[] = {1, 2, 3, 4};
+
+      std::same_as<std::ranges::subrange<It>> auto ret = std::ranges::find_last(It(a), Sent(It(a + 4)), 2);
+      assert(base(ret.begin()) == a + 1);
+      assert(*ret.begin() == 2);
+    }
+    {
+      ValueT a[] = {1, 2, 3, 4};
+      auto range = std::ranges::subrange(It(a), Sent(It(a + 4)));
+
+      std::same_as<std::ranges::subrange<It>> auto ret = std::ranges::find_last(range, 2);
+      assert(base(ret.begin()) == a + 1);
+      assert(*ret.begin() == 2);
+    }
+  }
+
+  { // check that an empty range works
+    {
+      std::array<ValueT, 0> a = {};
+
+      auto ret = std::ranges::find_last(It(a.data()), Sent(It(a.data())), 1).begin();
+      assert(base(ret) == a.data());
+    }
+    {
+      std::array<ValueT, 0> a = {};
+
+      auto range = std::ranges::subrange(It(a.data()), Sent(It(a.data())));
+      auto ret   = std::ranges::find_last(range, 1).begin();
+      assert(base(ret) == a.data());
+    }
+  }
+
+  { // check that last is returned with no match
+    {
+      ValueT a[] = {1, 1, 1};
+
+      auto ret = std::ranges::find_last(a, a + 3, 0).begin();
+      assert(ret == a + 3);
+    }
+    {
+      ValueT a[] = {1, 1, 1};
+
+      auto ret = std::ranges::find_last(a, 0).begin();
+      assert(ret == a + 3);
+    }
+  }
+
+  if (!std::is_constant_evaluated())
+    comparable_data.clear();
+}
+
+template <class ElementT>
+class TriviallyComparable {
+  ElementT el_;
+
+public:
+  TEST_CONSTEXPR TriviallyComparable(ElementT el) : el_(el) {}
+  bool operator==(const TriviallyComparable&) const = default;
+};
+
+constexpr bool test() {
+  types::for_each(types::type_list<char, wchar_t, int, long, TriviallyComparable<char>, TriviallyComparable<wchar_t>>{},
+                  []<class T> {
+                    types::for_each(types::forward_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>>();
+                    });
+                  });
+
+  {
+    std::vector<std::vector<int>> vec = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
+    auto view                         = vec | std::views::join;
+    assert(std::ranges::find_last(view.begin(), view.end(), 4).begin() == std::next(view.begin(), 3));
+    assert(std::ranges::find_last(view, 4).begin() == std::next(view.begin(), 3));
+  }
+
+  { // check that the last element is returned
+    {
+      struct S {
+        int comp;
+        int other;
+      };
+      S a[]    = {{0, 0}, {0, 2}, {0, 1}};
+      auto ret = std::ranges::find_last(a, 0, &S::comp).begin();
+      assert(ret == a + 2);
+      assert(ret->comp == 0);
+      assert(ret->other == 1);
+    }
+    {
+      struct S {
+        int comp;
+        int other;
+      };
+      S a[]    = {{0, 0}, {0, 2}, {0, 1}};
+      auto ret = std::ranges::find_last(a, a + 3, 0, &S::comp).begin();
+      assert(ret == a + 2);
+      assert(ret->comp == 0);
+      assert(ret->other == 1);
+    }
+  }
+
+  {
+    // check that an iterator is returned with a borrowing range
+    int a[]                                            = {1, 2, 3, 4};
+    std::same_as<std::ranges::subrange<int*>> auto ret = std::ranges::find_last(std::views::all(a), 1);
+    assert(ret.begin() == a);
+    assert(*ret.begin() == 1);
+  }
+
+  {
+    // count invocations of the projection
+    {
+      int a[]              = {1, 2, 3, 4};
+      int projection_count = 0;
+      auto ret             = std::ranges::find_last(a, a + 4, 2, [&](int i) {
+                   ++projection_count;
+                   return i;
+                 }).begin();
+      assert(ret == a + 1);
+      assert(*ret == 2);
+      assert(projection_count == 3);
+    }
+    {
+      int a[]              = {1, 2, 3, 4};
+      int projection_count = 0;
+      auto ret             = std::ranges::find_last(a, 2, [&](int i) {
+                   ++projection_count;
+                   return i;
+                 }).begin();
+      assert(ret == a + 1);
+      assert(*ret == 2);
+      assert(projection_count == 3);
+    }
+  }
+
+  return true;
+}
+
+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; }
+};
+
+void test_deque() {
----------------
strega-nil wrote:

Actually, I'm not sure it's useful to test all the sequence containers - it seems mostly like wasted compute. How about just testing a forward, bidirectional, and random access container?

https://github.com/llvm/llvm-project/pull/99312