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Modernized transform_iterator.hpp, use EBO to store the transform function.
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Andrey Semashev
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1a58ca89d1
commit
6e6def930f
@ -4,144 +4,138 @@
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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_TRANSFORM_ITERATOR_23022003THW_HPP
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#define BOOST_TRANSFORM_ITERATOR_23022003THW_HPP
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#ifndef BOOST_ITERATOR_TRANSFORM_ITERATOR_23022003THW_HPP
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#define BOOST_ITERATOR_TRANSFORM_ITERATOR_23022003THW_HPP
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#include <iterator>
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#include <type_traits>
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#include <boost/config.hpp>
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#include <boost/config/workaround.hpp>
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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/iterator/detail/eval_if_default.hpp>
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#include <boost/utility/result_of.hpp>
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#include <type_traits>
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#include <iterator>
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namespace boost {
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namespace iterators {
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template <class UnaryFunction, class Iterator, class Reference = use_default, class Value = use_default>
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class transform_iterator;
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template<
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typename UnaryFunction,
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typename Iterator,
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typename Reference = use_default,
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typename Value = use_default
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>
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class transform_iterator;
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namespace detail
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{
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// Compute the iterator_adaptor instantiation to be used for transform_iterator
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template <class UnaryFunc, class Iterator, class Reference, class Value>
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struct transform_iterator_base
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{
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private:
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// By default, dereferencing the iterator yields the same as
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// the function.
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using reference = detail::eval_if_default_t<
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Reference,
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#ifdef BOOST_RESULT_OF_USE_TR1
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result_of<const UnaryFunc(typename std::iterator_traits<Iterator>::reference)>
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#else
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result_of<const UnaryFunc&(typename std::iterator_traits<Iterator>::reference)>
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#endif
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>;
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namespace detail {
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// To get the default for Value: remove any reference on the
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// result type, but retain any constness to signal
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// non-writability. Note that if we adopt Thomas' suggestion
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// to key non-writability *only* on the Reference argument,
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// we'd need to strip constness here as well.
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using cv_value_type = detail::eval_if_default_t<
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Value,
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remove_reference<reference>
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>;
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template< typename UnaryFunc, typename Iterator >
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struct transform_iterator_default_reference
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{
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using type = decltype(std::declval< UnaryFunc const& >()(std::declval< typename std::iterator_traits< Iterator >::reference >()));
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};
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public:
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using type = iterator_adaptor<
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transform_iterator<UnaryFunc, Iterator, Reference, Value>,
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Iterator,
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cv_value_type,
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use_default, // Leave the traversal category alone
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reference
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>;
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};
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}
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// Compute the iterator_adaptor instantiation to be used for transform_iterator
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template< typename UnaryFunc, typename Iterator, typename Reference, typename Value >
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struct transform_iterator_base
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{
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private:
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// By default, dereferencing the iterator yields the same as
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// the function.
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using reference = detail::eval_if_default_t<
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Reference,
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transform_iterator_default_reference< UnaryFunc, Iterator >
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>;
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template <class UnaryFunc, class Iterator, class Reference, class Value>
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class transform_iterator
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: public boost::iterators::detail::transform_iterator_base<UnaryFunc, Iterator, Reference, Value>::type
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{
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typedef typename
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boost::iterators::detail::transform_iterator_base<UnaryFunc, Iterator, Reference, Value>::type
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super_t;
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// To get the default for Value: remove any reference on the
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// result type, but retain any constness to signal
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// non-writability. Note that if we adopt Thomas' suggestion
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// to key non-writability *only* on the Reference argument,
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// we'd need to strip constness here as well.
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using cv_value_type = detail::eval_if_default_t<
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Value,
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std::remove_reference< reference >
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>;
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public:
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using type = iterator_adaptor<
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transform_iterator< UnaryFunc, Iterator, Reference, Value >,
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Iterator,
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cv_value_type,
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use_default, // Leave the traversal category alone
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reference
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>;
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};
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} // namespace detail
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template< typename UnaryFunc, typename Iterator, typename Reference, typename Value >
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class transform_iterator :
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public detail::transform_iterator_base< UnaryFunc, Iterator, Reference, Value >::type,
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private boost::empty_value< UnaryFunc >
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{
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friend class iterator_core_access;
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public:
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transform_iterator() { }
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private:
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using super_t = typename detail::transform_iterator_base< UnaryFunc, Iterator, Reference, Value >::type;
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using functor_base = boost::empty_value< UnaryFunc >;
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transform_iterator(Iterator const& x, UnaryFunc f)
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: super_t(x), m_f(f) { }
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public:
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transform_iterator() = default;
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explicit transform_iterator(Iterator const& x)
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: super_t(x)
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{
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// Pro8 is a little too aggressive about instantiating the
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// body of this function.
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#if !BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3003))
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// don't provide this constructor if UnaryFunc is a
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// function pointer type, since it will be 0. Too dangerous.
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static_assert(std::is_class<UnaryFunc>::value, "Transform function must not be a function pointer.");
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#endif
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}
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transform_iterator(Iterator const& x, UnaryFunc f) :
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super_t(x),
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functor_base(boost::empty_init_t{}, f)
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{}
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template <
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class OtherUnaryFunction
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, class OtherIterator
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, class OtherReference
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, class OtherValue>
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transform_iterator(
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transform_iterator<OtherUnaryFunction, OtherIterator, OtherReference, OtherValue> const& t
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, typename enable_if_convertible<OtherIterator, Iterator>::type* = 0
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, typename enable_if_convertible<OtherUnaryFunction, UnaryFunc>::type* = 0
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)
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: super_t(t.base()), m_f(t.functor())
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{}
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// don't provide this constructor if UnaryFunc is a
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// function pointer type, since it will be 0. Too dangerous.
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template< bool Requires = std::is_class< UnaryFunc >::value, typename = typename std::enable_if< Requires >::type >
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explicit transform_iterator(Iterator const& x) :
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super_t(x)
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{}
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UnaryFunc functor() const
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{ return m_f; }
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template<
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typename OtherUnaryFunction,
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typename OtherIterator,
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typename OtherReference,
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typename OtherValue,
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typename = enable_if_convertible_t< OtherIterator, Iterator >,
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typename = enable_if_convertible_t< OtherUnaryFunction, UnaryFunc >
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>
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transform_iterator(transform_iterator< OtherUnaryFunction, OtherIterator, OtherReference, OtherValue > const& t) :
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super_t(t.base()),
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functor_base(boost::empty_init_t{}, t.functor())
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{}
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private:
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typename super_t::reference dereference() const
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{ return m_f(*this->base()); }
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UnaryFunc functor() const { return functor_base::get(); }
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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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UnaryFunc m_f;
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};
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private:
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typename super_t::reference dereference() const { return functor_base::get()(*this->base()); }
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};
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template <class UnaryFunc, class Iterator>
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inline transform_iterator<UnaryFunc, Iterator>
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make_transform_iterator(Iterator it, UnaryFunc fun)
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{
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return transform_iterator<UnaryFunc, Iterator>(it, fun);
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}
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template< typename UnaryFunc, typename Iterator >
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inline transform_iterator< UnaryFunc, Iterator > make_transform_iterator(Iterator it, UnaryFunc fun)
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{
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return transform_iterator< UnaryFunc, Iterator >(it, fun);
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}
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// Version which allows explicit specification of the UnaryFunc
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// type.
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//
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// This generator is not provided if UnaryFunc is a function
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// pointer type, because it's too dangerous: the default-constructed
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// function pointer in the iterator be 0, leading to a runtime
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// crash.
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template< typename UnaryFunc, typename Iterator >
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inline typename std::enable_if<
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std::is_class< UnaryFunc >::value, // We should probably find a cheaper test than is_class<>
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transform_iterator< UnaryFunc, Iterator >
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>::type make_transform_iterator(Iterator it)
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{
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return transform_iterator< UnaryFunc, Iterator >(it);
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}
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// Version which allows explicit specification of the UnaryFunc
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// type.
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//
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// This generator is not provided if UnaryFunc is a function
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// pointer type, because it's too dangerous: the default-constructed
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// function pointer in the iterator be 0, leading to a runtime
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// crash.
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template <class UnaryFunc, class Iterator>
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inline typename std::enable_if<
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std::is_class<UnaryFunc>::value // We should probably find a cheaper test than is_class<>
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, transform_iterator<UnaryFunc, Iterator>
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>::type
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make_transform_iterator(Iterator it)
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{
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return transform_iterator<UnaryFunc, Iterator>(it, UnaryFunc());
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}
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} // namespace iterators
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using iterators::transform_iterator;
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@ -149,4 +143,4 @@ using iterators::make_transform_iterator;
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} // namespace boost
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#endif // BOOST_TRANSFORM_ITERATOR_23022003THW_HPP
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#endif // BOOST_ITERATOR_TRANSFORM_ITERATOR_23022003THW_HPP
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