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8c2fdf6053
This results in marginally faster compile times in modern code bases where tuples are variadic.
369 lines
11 KiB
C++
369 lines
11 KiB
C++
// Copyright David Abrahams and Thomas Becker 2000-2006.
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// Copyright Kohei Takahashi 2012-2014.
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_ZIP_ITERATOR_TMB_07_13_2003_HPP_
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#define BOOST_ZIP_ITERATOR_TMB_07_13_2003_HPP_
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#include <utility> // for std::pair
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#include <boost/iterator/iterator_traits.hpp>
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#include <boost/iterator/iterator_facade.hpp>
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#include <boost/iterator/enable_if_convertible.hpp>
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#include <boost/iterator/iterator_categories.hpp>
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#include <boost/iterator/min_category.hpp>
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#include <boost/mp11/list.hpp>
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#include <boost/mp11/utility.hpp>
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#include <boost/fusion/adapted/boost_tuple.hpp> // for backward compatibility
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#include <boost/fusion/algorithm/iteration/for_each.hpp>
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#include <boost/fusion/algorithm/transformation/transform.hpp>
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#include <boost/fusion/sequence/convert.hpp>
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#include <boost/fusion/sequence/intrinsic/at_c.hpp>
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#include <boost/fusion/sequence/comparison/equal_to.hpp>
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#include <boost/fusion/support/tag_of_fwd.hpp>
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namespace boost {
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// Forward declarations for Boost.Tuple support
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namespace tuples {
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struct null_type;
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template< class, class >
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struct cons;
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} // namespace tuples
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// Forward declarations for Boost.Fusion support
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namespace fusion {
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struct void_;
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} // namespace fusion
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namespace iterators {
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// Zip iterator forward declaration for zip_iterator_base
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template< typename IteratorTuple >
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class zip_iterator;
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namespace detail {
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// Functors to be used with tuple algorithms
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//
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template< typename DiffType >
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class advance_iterator
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{
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public:
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advance_iterator(DiffType step) :
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m_step(step)
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{}
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template< typename Iterator >
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void operator()(Iterator& it) const { it += m_step; }
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private:
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DiffType m_step;
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};
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struct increment_iterator
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{
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template< typename Iterator >
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void operator()(Iterator& it) const { ++it; }
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};
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struct decrement_iterator
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{
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template< typename Iterator >
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void operator()(Iterator& it) const { --it; }
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};
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struct dereference_iterator
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{
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template< typename >
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struct result;
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template< typename This, typename Iterator >
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struct result< This(Iterator) >
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{
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using type = iterator_reference_t<
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typename std::remove_cv< typename std::remove_reference< Iterator >::type >::type
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>;
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};
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template< typename Iterator >
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typename result< dereference_iterator(Iterator) >::type operator()(Iterator const& it) const
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{
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return *it;
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}
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};
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// The trait checks if the type is a trailing "null" type used to indicate unused template parameters in non-variadic types
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template< typename T >
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struct is_trailing_null_type : std::false_type {};
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template< typename T >
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struct is_trailing_null_type< const T > : is_trailing_null_type< T > {};
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template< >
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struct is_trailing_null_type< tuples::null_type > : std::true_type {};
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template< >
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struct is_trailing_null_type< fusion::void_ > : std::true_type {};
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// Metafunction to obtain the type of the tuple whose element types
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// are the reference types of an iterator tuple.
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template< typename IteratorTuple >
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struct tuple_of_references;
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template< typename IteratorTuple >
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using tuple_of_references_t = typename tuple_of_references< IteratorTuple >::type;
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template< template< typename... > class Tuple, typename... Iterators >
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struct tuple_of_references< Tuple< Iterators... > >
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{
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// Note: non-variadic Boost.Tuple and Boost.Fusion need special handling
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// to avoid instantiating iterator traits on the trailing "null" types.
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// If not that, we could simply do
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// mp11::mp_transform< iterator_reference_t, IteratorTuple >.
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using type = Tuple<
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mp11::mp_eval_if<
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detail::is_trailing_null_type< Iterators >,
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Iterators,
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iterator_reference_t, Iterators
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>...
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>;
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};
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template< typename Front, typename Tail >
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struct tuple_of_references< tuples::cons< Front, Tail > >
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{
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using type = tuples::cons<
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iterator_reference_t< Front >,
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mp11::mp_eval_if<
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detail::is_trailing_null_type< Tail >,
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Tail,
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detail::tuple_of_references_t, Tail
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>
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>;
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};
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// Metafunction to obtain the minimal traversal tag in a list
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// of iterators.
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template< typename IteratorList >
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struct minimum_traversal_category_in_iterator_list;
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template< typename IteratorList >
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using minimum_traversal_category_in_iterator_list_t = typename minimum_traversal_category_in_iterator_list< IteratorList >::type;
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template< template< typename... > class List, typename... Iterators >
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struct minimum_traversal_category_in_iterator_list< List< Iterators... > >
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{
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// Note: non-variadic Boost.Tuple and Boost.Fusion need special handling
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// to avoid instantiating iterator traits on the trailing "null" types.
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// For such types just use random_access_traversal_tag, which will not
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// affect the result of min_category.
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using type = min_category_t<
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mp11::mp_eval_if<
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detail::is_trailing_null_type< Iterators >,
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random_access_traversal_tag,
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pure_iterator_traversal_t, Iterators
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>...
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>;
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};
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template< typename FrontTraversal, typename Tail >
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using minimum_traversal_category_in_tail_t = min_category_t<
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FrontTraversal,
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minimum_traversal_category_in_iterator_list_t< Tail >
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>;
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template< typename Front, typename Tail >
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struct minimum_traversal_category_in_iterator_list< tuples::cons< Front, Tail > >
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{
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using front_traversal = pure_iterator_traversal_t< Front >;
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using type = mp11::mp_eval_if<
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detail::is_trailing_null_type< Tail >,
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front_traversal,
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minimum_traversal_category_in_tail_t,
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front_traversal,
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Tail
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>;
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};
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///////////////////////////////////////////////////////////////////
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//
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// Class zip_iterator_base
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//
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// Builds and exposes the iterator facade type from which the zip
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// iterator will be derived.
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//
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template< typename IteratorTuple >
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struct zip_iterator_base
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{
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private:
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// Reference type is the type of the tuple obtained from the
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// iterators' reference types.
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using reference = detail::tuple_of_references_t< IteratorTuple >;
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// Value type is the same as reference type.
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using value_type = reference;
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// Difference type is the first iterator's difference type
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using difference_type = iterator_difference_t< mp11::mp_front< IteratorTuple > >;
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// Traversal catetgory is the minimum traversal category in the
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// iterator tuple.
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using traversal_category = detail::minimum_traversal_category_in_iterator_list_t< IteratorTuple >;
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public:
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// The iterator facade type from which the zip iterator will
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// be derived.
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using type = iterator_facade<
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zip_iterator< IteratorTuple >,
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value_type,
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traversal_category,
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reference,
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difference_type
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>;
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};
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template< typename Reference >
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struct converter
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{
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template< typename Seq >
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static Reference call(Seq seq)
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{
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using tag = typename fusion::traits::tag_of< Reference >::type;
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return fusion::convert< tag >(seq);
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}
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};
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template< typename Reference1, typename Reference2 >
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struct converter< std::pair< Reference1, Reference2 > >
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{
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using reference = std::pair< Reference1, Reference2 >;
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template< typename Seq >
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static reference call(Seq seq)
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{
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return reference(fusion::at_c< 0 >(seq), fusion::at_c< 1 >(seq));
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}
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};
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} // namespace detail
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/////////////////////////////////////////////////////////////////////
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//
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// zip_iterator class definition
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//
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template< typename IteratorTuple >
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class zip_iterator :
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public detail::zip_iterator_base< IteratorTuple >::type
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{
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// Typedef super_t as our base class.
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using super_t = typename detail::zip_iterator_base< IteratorTuple >::type;
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// iterator_core_access is the iterator's best friend.
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friend class iterator_core_access;
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public:
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// Construction
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// ============
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// Default constructor
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zip_iterator() = default;
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// Constructor from iterator tuple
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zip_iterator(IteratorTuple iterator_tuple) :
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m_iterator_tuple(iterator_tuple)
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{}
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// Copy constructor
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template< typename OtherIteratorTuple, typename = enable_if_convertible_t< OtherIteratorTuple, IteratorTuple > >
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zip_iterator(zip_iterator< OtherIteratorTuple > const& other) :
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m_iterator_tuple(other.get_iterator_tuple())
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{}
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// Get method for the iterator tuple.
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IteratorTuple const& get_iterator_tuple() const { return m_iterator_tuple; }
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private:
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// Implementation of Iterator Operations
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// =====================================
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// Dereferencing returns a tuple built from the dereferenced
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// iterators in the iterator tuple.
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typename super_t::reference dereference() const
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{
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using reference = typename super_t::reference;
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using gen = detail::converter< reference >;
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return gen::call(fusion::transform(get_iterator_tuple(), detail::dereference_iterator()));
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}
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// Two zip iterators are equal if all iterators in the iterator
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// tuple are equal. NOTE: It should be possible to implement this
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// as
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//
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// return get_iterator_tuple() == other.get_iterator_tuple();
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//
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// but equality of tuples currently (7/2003) does not compile
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// under several compilers. No point in bringing in a bunch
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// of #ifdefs here.
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//
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template< typename OtherIteratorTuple >
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bool equal(zip_iterator< OtherIteratorTuple > const& other) const
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{
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return fusion::equal_to(get_iterator_tuple(), other.get_iterator_tuple());
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}
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// Advancing a zip iterator means to advance all iterators in the
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// iterator tuple.
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void advance(typename super_t::difference_type n)
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{
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fusion::for_each(m_iterator_tuple, detail::advance_iterator< typename super_t::difference_type >(n));
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}
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// Incrementing a zip iterator means to increment all iterators in
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// the iterator tuple.
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void increment()
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{
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fusion::for_each(m_iterator_tuple, detail::increment_iterator());
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}
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// Decrementing a zip iterator means to decrement all iterators in
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// the iterator tuple.
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void decrement()
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{
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fusion::for_each(m_iterator_tuple, detail::decrement_iterator());
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}
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// Distance is calculated using the first iterator in the tuple.
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template< typename OtherIteratorTuple >
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typename super_t::difference_type distance_to(zip_iterator< OtherIteratorTuple > const& other) const
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{
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return fusion::at_c< 0 >(other.get_iterator_tuple()) - fusion::at_c< 0 >(this->get_iterator_tuple());
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}
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private:
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// Data Members
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// ============
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// The iterator tuple.
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IteratorTuple m_iterator_tuple;
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};
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// Make function for zip iterator
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//
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template< typename IteratorTuple >
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inline zip_iterator< IteratorTuple > make_zip_iterator(IteratorTuple t)
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{
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return zip_iterator< IteratorTuple >(t);
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}
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} // namespace iterators
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using iterators::zip_iterator;
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using iterators::make_zip_iterator;
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} // namespace boost
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#endif
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