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counting_iterator.hpp
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// Copyright David Abrahams 2003. // Distributed under the Boost Software License, Version 1.0. (See // accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) #ifndef COUNTING_ITERATOR_DWA200348_HPP # define COUNTING_ITERATOR_DWA200348_HPP # include <boost/iterator/iterator_adaptor.hpp> # include <boost/detail/numeric_traits.hpp> # include <boost/mpl/bool.hpp> # include <boost/mpl/if.hpp> # include <boost/mpl/identity.hpp> # include <boost/mpl/eval_if.hpp> namespace boost { namespace iterators { template < class Incrementable , class CategoryOrTraversal , class Difference > class counting_iterator; namespace detail { // Try to detect numeric types at compile time in ways compatible // with the limitations of the compiler and library. template <class T> struct is_numeric_impl { // For a while, this wasn't true, but we rely on it below. This is a regression assert. BOOST_STATIC_ASSERT(::boost::is_integral<char>::value); # ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS BOOST_STATIC_CONSTANT(bool, value = std::numeric_limits<T>::is_specialized); # else # if !BOOST_WORKAROUND(BOOST_BORLANDC, BOOST_TESTED_AT(0x551)) BOOST_STATIC_CONSTANT( bool, value = ( boost::is_convertible<int,T>::value && boost::is_convertible<T,int>::value )); # else BOOST_STATIC_CONSTANT(bool, value = ::boost::is_arithmetic<T>::value); # endif # endif }; template <class T> struct is_numeric : mpl::bool_<(::boost::iterators::detail::is_numeric_impl<T>::value)> {}; # if defined(BOOST_HAS_LONG_LONG) template <> struct is_numeric< ::boost::long_long_type> : mpl::true_ {}; template <> struct is_numeric< ::boost::ulong_long_type> : mpl::true_ {}; # endif // Some compilers fail to have a numeric_limits specialization template <> struct is_numeric<wchar_t> : mpl::true_ {}; template <class T> struct numeric_difference { typedef typename boost::detail::numeric_traits<T>::difference_type type; }; BOOST_STATIC_ASSERT(is_numeric<int>::value); template <class Incrementable, class CategoryOrTraversal, class Difference> struct counting_iterator_base { typedef typename detail::ia_dflt_help< CategoryOrTraversal , mpl::eval_if< is_numeric<Incrementable> , mpl::identity<random_access_traversal_tag> , iterator_traversal<Incrementable> > >::type traversal; typedef typename detail::ia_dflt_help< Difference , mpl::eval_if< is_numeric<Incrementable> , numeric_difference<Incrementable> , iterator_difference<Incrementable> > >::type difference; typedef iterator_adaptor< counting_iterator<Incrementable, CategoryOrTraversal, Difference> // self , Incrementable // Base , Incrementable // Value # ifndef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY const // MSVC won't strip this. Instead we enable Thomas' // criterion (see boost/iterator/detail/facade_iterator_category.hpp) # endif , traversal , Incrementable const& // reference , difference > type; }; // Template class distance_policy_select -- choose a policy for computing the // distance between counting_iterators at compile-time based on whether or not // the iterator wraps an integer or an iterator, using "poor man's partial // specialization". template <bool is_integer> struct distance_policy_select; // A policy for wrapped iterators template <class Difference, class Incrementable1, class Incrementable2> struct iterator_distance { static Difference distance(Incrementable1 x, Incrementable2 y) { return y - x; } }; // A policy for wrapped numbers template <class Difference, class Incrementable1, class Incrementable2> struct number_distance { static Difference distance(Incrementable1 x, Incrementable2 y) { return boost::detail::numeric_distance(x, y); } }; } template < class Incrementable , class CategoryOrTraversal = use_default , class Difference = use_default > class counting_iterator : public detail::counting_iterator_base< Incrementable, CategoryOrTraversal, Difference >::type { typedef typename detail::counting_iterator_base< Incrementable, CategoryOrTraversal, Difference >::type super_t; friend class iterator_core_access; public: typedef typename super_t::difference_type difference_type; counting_iterator() { } counting_iterator(counting_iterator const& rhs) : super_t(rhs.base()) {} counting_iterator(Incrementable x) : super_t(x) { } # if 0 template<class OtherIncrementable> counting_iterator( counting_iterator<OtherIncrementable, CategoryOrTraversal, Difference> const& t , typename enable_if_convertible<OtherIncrementable, Incrementable>::type* = 0 ) : super_t(t.base()) {} # endif private: typename super_t::reference dereference() const { return this->base_reference(); } template <class OtherIncrementable> difference_type distance_to(counting_iterator<OtherIncrementable, CategoryOrTraversal, Difference> const& y) const { typedef typename mpl::if_< detail::is_numeric<Incrementable> , detail::number_distance<difference_type, Incrementable, OtherIncrementable> , detail::iterator_distance<difference_type, Incrementable, OtherIncrementable> >::type d; return d::distance(this->base(), y.base()); } }; // Manufacture a counting iterator for an arbitrary incrementable type template <class Incrementable> inline counting_iterator<Incrementable> make_counting_iterator(Incrementable x) { typedef counting_iterator<Incrementable> result_t; return result_t(x); } } // namespace iterators using iterators::counting_iterator; using iterators::make_counting_iterator; } // namespace boost #endif // COUNTING_ITERATOR_DWA200348_HPP