147 lines
4.8 KiB
C++
147 lines
4.8 KiB
C++
/*
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* This file is part of the DXX-Rebirth project <http://www.dxx-rebirth.com/>.
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* It is copyright by its individual contributors, as recorded in the
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* project's Git history. See COPYING.txt at the top level for license
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* terms and a link to the Git history.
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*/
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#pragma once
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#include <iterator>
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#include <tuple>
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#include <type_traits>
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#include "dxxsconf.h"
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#include "ephemeral_range.h"
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#include <utility>
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namespace d_zip {
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namespace detail {
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template <typename... T>
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void discard_arguments(T &&...)
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{
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}
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template <std::size_t... N, typename... range_iterator_type>
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void increment_iterator(std::tuple<range_iterator_type...> &iterator, std::index_sequence<N...>)
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{
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/* Order of evaluation is irrelevant, so pass the results to a
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* discarding function. This permits the compiler to evaluate the
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* expression elements in any order.
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*/
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discard_arguments(++(std::get<N>(iterator))...);
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}
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template <std::size_t... N, typename... range_iterator_type>
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auto dereference_iterator(const std::tuple<range_iterator_type...> &iterator, std::index_sequence<N...>)
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{
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/* std::make_tuple is not appropriate here, because the result of
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* dereferencing the iterator may be a reference, and the resulting
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* tuple should store the reference, not the underlying object.
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* Calling std::make_tuple would decay such references into the
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* underlying type.
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*
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* std::tie is not appropriate here, because it captures all
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* arguments as `T &`, so it fails to compile if the result of
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* dereferencing the iterator is not a reference.
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*/
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return std::tuple<
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decltype(*(std::get<N>(iterator)))...
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>(*(std::get<N>(iterator))...);
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}
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}
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}
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/* This iterator terminates when the first zipped range terminates. The
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* caller is responsible for ensuring that use of the zip_iterator does
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* not increment past the end of any zipped range. This can be done by
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* ensuring that the first zipped range is not longer than any other
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* zipped range, or by ensuring that external logic stops the traversal
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* before the zip_iterator increments past the end.
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*
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* There is no initialization time check that the below loop would be
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* safe, since a check external to the zip_iterator could stop before
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* undefined behaviour occurs.
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for (auto i = zip_range.begin(), e = zip_range.end(); i != e; ++i)
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{
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if (condition())
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break;
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}
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*/
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template <typename... range_iterator_type>
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class zip_iterator : std::tuple<range_iterator_type...>
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{
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using base_type = std::tuple<range_iterator_type...>;
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protected:
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/* Prior to C++17, range-based for insisted on the same type for
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* `begin` and `end`, so method `end_internal` must return a full iterator,
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* even though most of it is a waste. To save some work, values that are
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* used for ignored fields are default-constructed (if possible)
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* instead of copy-constructed from the begin iterator.
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*/
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template <std::size_t I, typename T>
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static typename std::enable_if<std::is_default_constructible<T>::value, T>::type end_construct_ignored_element()
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{
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return T();
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}
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template <std::size_t I, typename T>
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typename std::enable_if<!std::is_default_constructible<T>::value, T>::type end_construct_ignored_element() const
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{
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return std::get<I>(*this);
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}
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template <typename E0, std::size_t... N>
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zip_iterator end_internal(const E0 &e0, std::index_sequence<0, N...>) const
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{
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return zip_iterator(e0, this->template end_construct_ignored_element<N, typename std::tuple_element<N, base_type>::type>()...);
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}
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using index_type = std::make_index_sequence<sizeof...(range_iterator_type)>;
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public:
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using base_type::base_type;
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auto operator*() const
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{
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return d_zip::detail::dereference_iterator(*this, index_type());
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}
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zip_iterator &operator++()
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{
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d_zip::detail::increment_iterator(*this, index_type());
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return *this;
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}
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bool operator!=(const zip_iterator &i) const
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{
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return std::get<0>(*this) != std::get<0>(i);
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}
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bool operator==(const zip_iterator &i) const
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{
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return !(*this != i);
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}
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};
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template <typename range0_iterator_type, typename... rangeN_iterator_type>
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class zip : zip_iterator<range0_iterator_type, rangeN_iterator_type...>
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{
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range0_iterator_type m_end;
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public:
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using range_owns_iterated_storage = std::false_type;
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using iterator = zip_iterator<range0_iterator_type, rangeN_iterator_type...>;
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template <typename range0, typename... rangeN>
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zip(range0 &&r0, rangeN &&... rN) :
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iterator(std::begin(r0), std::begin(rN)...), m_end(std::end(r0))
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{
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static_assert((!any_ephemeral_range<range0 &&, rangeN &&...>::value), "cannot zip storage of ephemeral ranges");
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}
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__attribute_warn_unused_result
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iterator begin() const { return *this; }
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__attribute_warn_unused_result
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iterator end() const
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{
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return this->end_internal(m_end, typename iterator::index_type());
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}
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};
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template <typename range0, typename... rangeN>
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zip(range0 &&r0, rangeN &&... rN) -> zip<decltype(std::begin(r0)), decltype(std::begin(rN))...>;
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