iterator_traits_test_helper.h (2971B)
1 // Copyright 2025 The Abseil Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_ 16 #define ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_ 17 18 #include <iterator> 19 #include <utility> 20 21 #include "absl/base/config.h" 22 23 namespace absl { 24 ABSL_NAMESPACE_BEGIN 25 namespace base_internal { 26 27 // This would be a forward_iterator in C++20, but it's only an input iterator 28 // before that, since it has a non-reference `reference`. 29 template <typename Iterator> 30 class Cpp20ForwardZipIterator { 31 using IteratorReference = typename std::iterator_traits<Iterator>::reference; 32 33 public: 34 Cpp20ForwardZipIterator() = default; 35 explicit Cpp20ForwardZipIterator(Iterator left, Iterator right) 36 : left_(left), right_(right) {} 37 38 Cpp20ForwardZipIterator& operator++() { 39 ++left_; 40 ++right_; 41 return *this; 42 } 43 44 Cpp20ForwardZipIterator operator++(int) { 45 Cpp20ForwardZipIterator tmp(*this); 46 ++*this; 47 return *this; 48 } 49 50 std::pair<IteratorReference, IteratorReference> operator*() const { 51 return {*left_, *right_}; 52 } 53 54 // C++17 input iterators require `operator->`, but this isn't possible to 55 // implement. C++20 dropped the requirement. 56 57 friend bool operator==(const Cpp20ForwardZipIterator& lhs, 58 const Cpp20ForwardZipIterator& rhs) { 59 return lhs.left_ == rhs.left_ && lhs.right_ == rhs.right_; 60 } 61 62 friend bool operator!=(const Cpp20ForwardZipIterator& lhs, 63 const Cpp20ForwardZipIterator& rhs) { 64 return !(lhs == rhs); 65 } 66 67 private: 68 Iterator left_{}; 69 Iterator right_{}; 70 }; 71 72 } // namespace base_internal 73 ABSL_NAMESPACE_END 74 } // namespace absl 75 76 template <typename Iterator> 77 struct std::iterator_traits< 78 absl::base_internal::Cpp20ForwardZipIterator<Iterator>> { 79 private: 80 using IteratorReference = typename std::iterator_traits<Iterator>::reference; 81 82 public: 83 using iterator_category = std::input_iterator_tag; 84 using iterator_concept = std::forward_iterator_tag; 85 using value_type = std::pair<IteratorReference, IteratorReference>; 86 using difference_type = 87 typename std::iterator_traits<Iterator>::difference_type; 88 using reference = value_type; 89 using pointer = void; 90 }; 91 92 #if defined(__cpp_lib_concepts) 93 static_assert( 94 std::forward_iterator<absl::base_internal::Cpp20ForwardZipIterator<int*>>); 95 #endif // defined(__cpp_lib_concepts) 96 97 #endif // ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_