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https://github.com/boostorg/iterator.git
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Modernized filter_iterator.hpp.
Use EBO to minimize wasted storage space if the predicate is an empty class. Disable default constructing non-class predicates using SFINAE instead of a static_assert. This will help type traits like is_constructible, when applied to the iterator type.
This commit is contained in:
Andrey Semashev
parent
baf6d06cc2
commit
dc57bcf319
@ -9,119 +9,140 @@
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#include <type_traits>
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#include <boost/core/use_default.hpp>
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#include <boost/core/empty_value.hpp>
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#include <boost/iterator/iterator_adaptor.hpp>
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#include <boost/iterator/iterator_categories.hpp>
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#include <boost/iterator/enable_if_convertible.hpp>
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#include <boost/core/use_default.hpp>
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namespace boost {
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namespace iterators {
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template <class Predicate, class Iterator>
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class filter_iterator;
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template< typename Predicate, typename Iterator >
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class filter_iterator;
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namespace detail
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{
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template <class Predicate, class Iterator>
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struct filter_iterator_base
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namespace detail {
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template< typename Predicate, typename Iterator >
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using filter_iterator_base_t = iterator_adaptor<
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filter_iterator< Predicate, Iterator >,
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Iterator,
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use_default,
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typename std::conditional<
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std::is_convertible<
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iterator_traversal_t< Iterator >,
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random_access_traversal_tag
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>::value,
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bidirectional_traversal_tag,
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use_default
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>::type
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>;
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} // namespace detail
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template< typename Predicate, typename Iterator >
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class filter_iterator :
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public detail::filter_iterator_base_t< Predicate, Iterator >
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{
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friend class iterator_core_access;
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private:
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using super_t = detail::filter_iterator_base_t< Predicate, Iterator >;
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// Storage class to leverage EBO, when possible
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struct storage :
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private boost::empty_value< Predicate >
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{
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typedef iterator_adaptor<
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filter_iterator<Predicate, Iterator>
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, Iterator
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, use_default
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, typename std::conditional<
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std::is_convertible<
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typename iterator_traversal<Iterator>::type
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, random_access_traversal_tag
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using predicate_base = boost::empty_value< Predicate >;
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Iterator m_end;
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storage() = default;
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template<
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typename Iter,
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typename = typename std::enable_if<
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!std::is_same<
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typename std::remove_cv< typename std::remove_reference< Iter >::type >::type,
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storage
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>::value
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, bidirectional_traversal_tag
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, use_default
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>::type
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> type;
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>
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>
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explicit storage(Iter&& end) :
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predicate_base(boost::empty_init_t{}), m_end(static_cast< Iterator&& >(end))
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{
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}
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template< typename Pred, typename Iter >
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storage(Pred&& pred, Iter&& end) :
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predicate_base(boost::empty_init_t{}, static_cast< Predicate&& >(pred)), m_end(static_cast< Iterator&& >(end))
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{
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}
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Predicate& predicate() noexcept { return predicate_base::get(); }
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Predicate const& predicate() const noexcept { return predicate_base::get(); }
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};
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}
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template <class Predicate, class Iterator>
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class filter_iterator
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: public detail::filter_iterator_base<Predicate, Iterator>::type
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{
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typedef typename detail::filter_iterator_base<
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Predicate, Iterator
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>::type super_t;
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public:
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filter_iterator() = default;
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friend class iterator_core_access;
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filter_iterator(Predicate f, Iterator x, Iterator end = Iterator()) :
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super_t(static_cast< Iterator&& >(x)), m_storage(static_cast< Predicate&& >(f), static_cast< Iterator&& >(end))
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{
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satisfy_predicate();
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}
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public:
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filter_iterator() { }
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template< bool Requires = std::is_class< Predicate >::value, typename = typename std::enable_if< Requires >::type >
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filter_iterator(Iterator x, Iterator end = Iterator()) :
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super_t(static_cast< Iterator&& >(x)), m_storage(static_cast< Iterator&& >(end))
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{
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satisfy_predicate();
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}
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filter_iterator(Predicate f, Iterator x, Iterator end_ = Iterator())
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: super_t(static_cast<Iterator&&>(x)), m_predicate(static_cast<Predicate&&>(f)), m_end(static_cast<Iterator&&>(end_))
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{
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satisfy_predicate();
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}
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template< typename OtherIterator, typename = enable_if_convertible_t< OtherIterator, Iterator > >
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filter_iterator(filter_iterator< Predicate, OtherIterator > const& t) :
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super_t(t.base()), m_storage(t.m_storage.predicate(), m_storage.m_end)
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{}
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filter_iterator(Iterator x, Iterator end_ = Iterator())
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: super_t(static_cast<Iterator&&>(x)), m_predicate(), m_end(static_cast<Iterator&&>(end_))
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{
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// Don't allow use of this constructor if Predicate is a
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// function pointer type, since it will be 0.
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static_assert(std::is_class<Predicate>::value, "Predicate must be a class.");
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satisfy_predicate();
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}
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Predicate predicate() const { return m_storage.predicate(); }
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Iterator end() const { return m_storage.m_end; }
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template<class OtherIterator>
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filter_iterator(
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filter_iterator<Predicate, OtherIterator> const& t
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, typename enable_if_convertible<OtherIterator, Iterator>::type* = 0
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)
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: super_t(t.base()), m_predicate(t.predicate()), m_end(t.end()) {}
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private:
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void increment()
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{
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++(this->base_reference());
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satisfy_predicate();
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}
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Predicate predicate() const { return m_predicate; }
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void decrement()
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{
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while (!m_storage.predicate()(*--(this->base_reference()))) {}
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}
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Iterator end() const { return m_end; }
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void satisfy_predicate()
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{
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while (this->base() != m_storage.m_end && !m_storage.predicate()(*this->base()))
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++(this->base_reference());
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}
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private:
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void increment()
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{
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++(this->base_reference());
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satisfy_predicate();
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}
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private:
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storage m_storage;
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};
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void decrement()
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{
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while(!this->m_predicate(*--(this->base_reference()))){};
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}
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template< typename Predicate, typename Iterator >
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inline filter_iterator< Predicate, Iterator > make_filter_iterator(Predicate f, Iterator x, Iterator end = Iterator())
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{
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return filter_iterator< Predicate, Iterator >(static_cast< Predicate&& >(f), static_cast< Iterator&& >(x), static_cast< Iterator&& >(end));
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}
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void satisfy_predicate()
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{
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while (this->base() != this->m_end && !this->m_predicate(*this->base()))
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++(this->base_reference());
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}
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// Probably should be the initial base class so it can be
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// optimized away via EBO if it is an empty class.
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Predicate m_predicate;
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Iterator m_end;
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};
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template <class Predicate, class Iterator>
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inline filter_iterator<Predicate,Iterator>
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make_filter_iterator(Predicate f, Iterator x, Iterator end = Iterator())
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{
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return filter_iterator<Predicate,Iterator>(static_cast<Predicate&&>(f), static_cast<Iterator&&>(x), static_cast<Iterator&&>(end));
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}
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template <class Predicate, class Iterator>
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inline filter_iterator<Predicate,Iterator>
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make_filter_iterator(
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typename std::enable_if<
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std::is_class<Predicate>::value
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, Iterator
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>::type x
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, Iterator end = Iterator())
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{
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return filter_iterator<Predicate,Iterator>(static_cast<Iterator&&>(x), static_cast<Iterator&&>(end));
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}
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template< typename Predicate, typename Iterator >
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inline typename std::enable_if<
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std::is_class< Predicate >::value,
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filter_iterator< Predicate, Iterator >
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>::type make_filter_iterator(Iterator x, Iterator end = Iterator())
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{
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return filter_iterator< Predicate, Iterator >(static_cast< Iterator&& >(x), static_cast< Iterator&& >(end));
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}
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} // namespace iterators
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