1e20f06c21
The difficulty of implementing this iterator is that it requires lots of operator overloads which are usually very simple to implement, but result in a lot of code. The goal of this patch is to abstract the common parts so that it becomes easier to implement random accessor iterators. Many algorithms can work more efficiently with random access iterators than with other iterator types. Also see https://en.cppreference.com/w/cpp/iterator/random_access_iterator Pull Request: https://projects.blender.org/blender/blender/pulls/118113
134 lines
3.3 KiB
C++
134 lines
3.3 KiB
C++
/* SPDX-FileCopyrightText: 2024 Blender Authors
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*
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* SPDX-License-Identifier: GPL-2.0-or-later */
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#pragma once
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#include <iterator>
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namespace blender::iterator {
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/**
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* Simplifies implementing a random-access-iterator.
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*
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* The actual iterator should derive from this class publicly. Additionally, it has to provide a
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* const `iter_prop` method which returns a reference to the internal property that corresponds to
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* the current position. This is typically a pointer or an index.
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*
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* Implementing some random-access-iterator is generally quite simple but requires a lot of
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* boilerplate code because algorithms expect many operators to work on the iterator type.
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* They are expected to behave similarly to pointers and thus have to implement many of the same
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* operators.
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*/
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template<typename Derived> class RandomAccessIteratorMixin {
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public:
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using iterator_category = std::random_access_iterator_tag;
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using difference_type = std::ptrdiff_t;
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constexpr friend Derived &operator++(Derived &a)
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{
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++a.iter_prop_mutable();
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return a;
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}
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constexpr friend Derived operator++(Derived &a, int)
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{
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Derived copy = a;
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++a;
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return copy;
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}
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constexpr friend Derived &operator--(Derived &a)
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{
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--a.iter_prop_mutable();
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return a;
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}
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constexpr friend Derived operator--(Derived &a, int)
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{
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Derived copy = a;
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--a;
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return copy;
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}
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constexpr friend Derived &operator+=(Derived &a, const std::ptrdiff_t n)
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{
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a.iter_prop_mutable() += n;
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return a;
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}
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constexpr friend Derived &operator-=(Derived &a, const std::ptrdiff_t n)
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{
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a.iter_prop_mutable() -= n;
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return a;
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}
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constexpr friend Derived operator+(const Derived &a, const std::ptrdiff_t n)
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{
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Derived copy = a;
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copy.iter_prop_mutable() += n;
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return copy;
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}
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constexpr friend Derived operator-(const Derived &a, const std::ptrdiff_t n)
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{
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Derived copy = a;
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copy.iter_prop_mutable() -= n;
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return copy;
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}
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constexpr friend auto operator-(const Derived &a, const Derived &b)
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{
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return a.iter_prop() - b.iter_prop();
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}
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constexpr friend bool operator!=(const Derived &a, const Derived &b)
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{
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return a.iter_prop() != b.iter_prop();
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}
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constexpr friend bool operator==(const Derived &a, const Derived &b)
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{
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return a.iter_prop() == b.iter_prop();
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}
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constexpr friend bool operator<(const Derived &a, const Derived &b)
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{
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return a.iter_prop() < b.iter_prop();
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}
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constexpr friend bool operator>(const Derived &a, const Derived &b)
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{
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return a.iter_prop() > b.iter_prop();
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}
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constexpr friend bool operator<=(const Derived &a, const Derived &b)
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{
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return a.iter_prop() <= b.iter_prop();
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}
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constexpr friend bool operator>=(const Derived &a, const Derived &b)
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{
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return a.iter_prop() >= b.iter_prop();
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}
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constexpr decltype(auto) operator[](const std::ptrdiff_t i)
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{
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return *(*static_cast<Derived *>(this) + i);
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}
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constexpr decltype(auto) operator[](const std::ptrdiff_t i) const
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{
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return *(*static_cast<const Derived *>(this) + i);
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}
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auto &iter_prop_mutable()
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{
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const auto &const_iter_prop = static_cast<const Derived *>(this)->iter_prop();
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return const_cast<std::remove_const_t<std::remove_reference_t<decltype(const_iter_prop)>> &>(
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const_iter_prop);
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}
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};
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} // namespace blender::iterator
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