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// Copyright 2025 The Abseil Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_
#define ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_
#include <iterator>
#include <utility>
#include "absl/base/config.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace base_internal {
// This would be a forward_iterator in C++20, but it's only an input iterator
// before that, since it has a non-reference `reference`.
template <typename Iterator>
class Cpp20ForwardZipIterator {
using IteratorReference = typename std::iterator_traits<Iterator>::reference;
public:
Cpp20ForwardZipIterator() = default;
explicit Cpp20ForwardZipIterator(Iterator left, Iterator right)
: left_(left), right_(right) {}
Cpp20ForwardZipIterator& operator++() {
++left_;
++right_;
return *this;
}
Cpp20ForwardZipIterator operator++(int) {
Cpp20ForwardZipIterator tmp(*this);
++*this;
return *this;
}
std::pair<IteratorReference, IteratorReference> operator*() const {
return {*left_, *right_};
}
// C++17 input iterators require `operator->`, but this isn't possible to
// implement. C++20 dropped the requirement.
friend bool operator==(const Cpp20ForwardZipIterator& lhs,
const Cpp20ForwardZipIterator& rhs) {
return lhs.left_ == rhs.left_ && lhs.right_ == rhs.right_;
}
friend bool operator!=(const Cpp20ForwardZipIterator& lhs,
const Cpp20ForwardZipIterator& rhs) {
return !(lhs == rhs);
}
private:
Iterator left_{};
Iterator right_{};
};
} // namespace base_internal
ABSL_NAMESPACE_END
} // namespace absl
template <typename Iterator>
struct std::iterator_traits<
absl::base_internal::Cpp20ForwardZipIterator<Iterator>> {
private:
using IteratorReference = typename std::iterator_traits<Iterator>::reference;
public:
using iterator_category = std::input_iterator_tag;
using iterator_concept = std::forward_iterator_tag;
using value_type = std::pair<IteratorReference, IteratorReference>;
using difference_type =
typename std::iterator_traits<Iterator>::difference_type;
using reference = value_type;
using pointer = void;
};
#if defined(__cpp_lib_concepts)
static_assert(
std::forward_iterator<absl::base_internal::Cpp20ForwardZipIterator<int*>>);
#endif // defined(__cpp_lib_concepts)
#endif // ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_
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