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Some forward iterators (by C++20's definition) are only input iterators in C++17 or before, because they cannot have a language reference for their `reference` type, e.g. a zip iterator. However, we can still use the fast paths for these iterators. E.g. this makes `absl::InlinedVector::insert(iterator, InputIt, InputIt)` faster for this category of forward iterator. `iterator_concept` was added in C++20, but it's reasonable to support this for pre-C++20 code as well. PiperOrigin-RevId: 725791745 Change-Id: I7dd02eef0b94ea6d4bfbda8f7f72db4abea10440
98 lines
2.9 KiB
C++
98 lines
2.9 KiB
C++
// Copyright 2025 The Abseil Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_
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#define ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_
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#include <iterator>
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#include <utility>
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#include "absl/base/config.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace base_internal {
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// This would be a forward_iterator in C++20, but it's only an input iterator
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// before that, since it has a non-reference `reference`.
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template <typename Iterator>
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class Cpp20ForwardZipIterator {
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using IteratorReference = typename std::iterator_traits<Iterator>::reference;
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public:
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Cpp20ForwardZipIterator() = default;
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explicit Cpp20ForwardZipIterator(Iterator left, Iterator right)
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: left_(left), right_(right) {}
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Cpp20ForwardZipIterator& operator++() {
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++left_;
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++right_;
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return *this;
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}
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Cpp20ForwardZipIterator operator++(int) {
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Cpp20ForwardZipIterator tmp(*this);
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++*this;
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return *this;
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}
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std::pair<IteratorReference, IteratorReference> operator*() const {
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return {*left_, *right_};
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}
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// C++17 input iterators require `operator->`, but this isn't possible to
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// implement. C++20 dropped the requirement.
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friend bool operator==(const Cpp20ForwardZipIterator& lhs,
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const Cpp20ForwardZipIterator& rhs) {
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return lhs.left_ == rhs.left_ && lhs.right_ == rhs.right_;
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}
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friend bool operator!=(const Cpp20ForwardZipIterator& lhs,
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const Cpp20ForwardZipIterator& rhs) {
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return !(lhs == rhs);
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}
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private:
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Iterator left_{};
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Iterator right_{};
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};
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} // namespace base_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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template <typename Iterator>
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struct std::iterator_traits<
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absl::base_internal::Cpp20ForwardZipIterator<Iterator>> {
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private:
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using IteratorReference = typename std::iterator_traits<Iterator>::reference;
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public:
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using iterator_category = std::input_iterator_tag;
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using iterator_concept = std::forward_iterator_tag;
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using value_type = std::pair<IteratorReference, IteratorReference>;
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using difference_type =
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typename std::iterator_traits<Iterator>::difference_type;
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using reference = value_type;
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using pointer = void;
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};
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#if defined(__cpp_lib_concepts)
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static_assert(
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std::forward_iterator<absl::base_internal::Cpp20ForwardZipIterator<int*>>);
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#endif // defined(__cpp_lib_concepts)
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#endif // ABSL_BASE_INTERNAL_ITERATOR_TRAITS_TEST_HELPER_H_
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