// Copyright 2019 Hans Dembinski
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//
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// Uses code segments from boost/iterator/iterator_adaptor.hpp
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// and boost/iterator/iterator_fascade.hpp
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#ifndef BOOST_HISTOGRAM_DETAIL_ITERATOR_ADAPTOR_HPP
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#define BOOST_HISTOGRAM_DETAIL_ITERATOR_ADAPTOR_HPP
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#include <iterator>
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#include <memory>
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#include <type_traits>
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#include <utility>
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namespace boost {
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namespace histogram {
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namespace detail {
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// operator->() needs special support for input iterators to strictly meet the
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// standard's requirements. If *i is not a reference type, we must still
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// produce an lvalue to which a pointer can be formed. We do that by
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// returning a proxy object containing an instance of the reference object.
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template <class Reference>
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struct operator_arrow_dispatch_t // proxy references
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{
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struct proxy {
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explicit proxy(Reference const& x) noexcept : m_ref(x) {}
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Reference* operator->() noexcept { return std::addressof(m_ref); }
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Reference m_ref;
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};
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using result_type = proxy;
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static result_type apply(Reference const& x) noexcept { return proxy(x); }
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};
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template <class T>
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struct operator_arrow_dispatch_t<T&> // "real" references
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{
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using result_type = T*;
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static result_type apply(T& x) noexcept { return std::addressof(x); }
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};
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// only for random access Base
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template <class Derived, class Base, class Reference = std::remove_pointer_t<Base>&,
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class Value = std::decay_t<Reference>>
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class iterator_adaptor {
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using operator_arrow_dispatch = operator_arrow_dispatch_t<Reference>;
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public:
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using base_type = Base;
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using reference = Reference;
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using value_type = std::remove_const_t<Value>;
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using pointer = typename operator_arrow_dispatch::result_type;
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using difference_type = std::ptrdiff_t;
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using iterator_category = std::random_access_iterator_tag;
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iterator_adaptor() = default;
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explicit iterator_adaptor(base_type const& iter) : iter_(iter) {}
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pointer operator->() const noexcept {
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return operator_arrow_dispatch::apply(this->derived().operator*());
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}
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reference operator[](difference_type n) const { return *(this->derived() + n); }
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Derived& operator++() {
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++iter_;
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return this->derived();
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}
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Derived& operator--() {
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--iter_;
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return this->derived();
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}
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Derived operator++(int) {
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Derived tmp(this->derived());
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++iter_;
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return tmp;
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}
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Derived operator--(int) {
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Derived tmp(this->derived());
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--iter_;
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return tmp;
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}
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Derived& operator+=(difference_type n) {
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iter_ += n;
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return this->derived();
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}
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Derived& operator-=(difference_type n) {
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iter_ -= n;
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return this->derived();
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}
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Derived operator+(difference_type n) const {
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Derived tmp(this->derived());
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tmp += n;
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return tmp;
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}
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Derived operator-(difference_type n) const { return operator+(-n); }
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template <class... Ts>
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difference_type operator-(const iterator_adaptor<Ts...>& x) const noexcept {
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return iter_ - x.iter_;
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}
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template <class... Ts>
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bool operator==(const iterator_adaptor<Ts...>& x) const noexcept {
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return iter_ == x.iter_;
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}
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template <class... Ts>
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bool operator!=(const iterator_adaptor<Ts...>& x) const noexcept {
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return !this->derived().operator==(x); // equal operator may be overridden in derived
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}
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template <class... Ts>
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bool operator<(const iterator_adaptor<Ts...>& x) const noexcept {
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return iter_ < x.iter_;
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}
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template <class... Ts>
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bool operator>(const iterator_adaptor<Ts...>& x) const noexcept {
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return iter_ > x.iter_;
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}
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template <class... Ts>
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bool operator<=(const iterator_adaptor<Ts...>& x) const noexcept {
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return iter_ <= x.iter_;
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}
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template <class... Ts>
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bool operator>=(const iterator_adaptor<Ts...>& x) const noexcept {
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return iter_ >= x.iter_;
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}
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friend Derived operator+(difference_type n, const Derived& x) { return x + n; }
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Base const& base() const noexcept { return iter_; }
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protected:
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// for convenience in derived classes
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using iterator_adaptor_ = iterator_adaptor;
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private:
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Derived& derived() noexcept { return *static_cast<Derived*>(this); }
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const Derived& derived() const noexcept { return *static_cast<Derived const*>(this); }
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Base iter_;
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template <class, class, class, class>
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friend class iterator_adaptor;
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};
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} // namespace detail
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} // namespace histogram
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} // namespace boost
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#endif
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