zip_iterator.hpp

来自「support vector clustering for vc++」· HPP 代码 · 共 586 行 · 第 1/2 页

      {
          return tuple_for_each_impl(t, f, 1);
      }
#endif
      
      // Equality of tuples. NOTE: "==" for tuples currently (7/2003)
      // has problems under some compilers, so I just do my own.
      // No point in bringing in a bunch of #ifdefs here. This is
      // going to go away with the next tuple implementation anyway.
      //
      inline bool tuple_equal(tuples::null_type, tuples::null_type)
      { return true; }

      template<typename Tuple1, typename Tuple2>
        bool tuple_equal(
            Tuple1 const& t1, 
            Tuple2 const& t2
        )
      { 
          return t1.get_head() == t2.get_head() && 
          tuple_equal(t1.get_tail(), t2.get_tail());
      }
    }
    //
    // end namespace tuple_impl_specific

    template<typename Iterator>
    struct iterator_reference
    {
        typedef typename iterator_traits<Iterator>::reference type;
    };

#ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
    // Hack because BOOST_MPL_AUX_LAMBDA_SUPPORT doesn't seem to work
    // out well.  Instantiating the nested apply template also
    // requires instantiating iterator_traits on the
    // placeholder. Instead we just specialize it as a metafunction
    // class.
    template<>
    struct iterator_reference<mpl::_1>
    {
        template <class T>
        struct apply : iterator_reference<T> {};
    };
#endif
    
    // Metafunction to obtain the type of the tuple whose element types
    // are the reference types of an iterator tuple.
    //
    template<typename IteratorTuple>
    struct tuple_of_references
      : tuple_impl_specific::tuple_meta_transform<
            IteratorTuple, 
            iterator_reference<mpl::_1>
          >
    {
    };

    // Metafunction to obtain the minimal traversal tag in a tuple
    // of iterators.
    //
    template<typename IteratorTuple>
    struct minimum_traversal_category_in_iterator_tuple
    {
      typedef typename tuple_impl_specific::tuple_meta_transform<
          IteratorTuple
        , iterator_traversal<>
      >::type tuple_of_traversal_tags;
          
      typedef typename tuple_impl_specific::tuple_meta_accumulate<
          tuple_of_traversal_tags
        , minimum_category<>
        , random_access_traversal_tag
      >::type type;
    };

#if BOOST_WORKAROUND(BOOST_MSVC, < 1300) // ETI workaround
      template <>
      struct minimum_traversal_category_in_iterator_tuple<int>
      {
          typedef int type;
      };
#endif
      
      // We need to call tuple_meta_accumulate with mpl::and_ as the
      // accumulating functor. To this end, we need to wrap it into
      // a struct that has exactly two arguments (that is, template
      // parameters) and not five, like mpl::and_ does.
      //
      template<typename Arg1, typename Arg2>
      struct and_with_two_args
        : mpl::and_<Arg1, Arg2>
      {
      };
    
# ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
  // Hack because BOOST_MPL_AUX_LAMBDA_SUPPORT doesn't seem to work
  // out well.  In this case I think it's an MPL bug
      template<>
      struct and_with_two_args<mpl::_1,mpl::_2>
      {
          template <class A1, class A2>
          struct apply : mpl::and_<A1,A2>
          {};
      };
# endif 

    ///////////////////////////////////////////////////////////////////
    //
    // Class zip_iterator_base
    //
    // Builds and exposes the iterator facade type from which the zip 
    // iterator will be derived.
    //
    template<typename IteratorTuple>
    struct zip_iterator_base
    {
     private:
        // Reference type is the type of the tuple obtained from the
        // iterators' reference types.
        typedef typename 
        detail::tuple_of_references<IteratorTuple>::type reference;
      
        // Value type is the same as reference type.
        typedef reference value_type;
      
        // Difference type is the first iterator's difference type
        typedef typename iterator_traits<
            typename tuples::element<0, IteratorTuple>::type
            >::difference_type difference_type;
      
        // Traversal catetgory is the minimum traversal category in the 
        // iterator tuple.
        typedef typename 
        detail::minimum_traversal_category_in_iterator_tuple<
            IteratorTuple
        >::type traversal_category;
     public:
      
        // The iterator facade type from which the zip iterator will
        // be derived.
        typedef iterator_facade<
            zip_iterator<IteratorTuple>,
            value_type,  
            traversal_category,
            reference,
            difference_type
        > type;
    };

    template <>
    struct zip_iterator_base<int>
    {
        typedef int type;
    };
  }
  
  /////////////////////////////////////////////////////////////////////
  //
  // zip_iterator class definition
  //
  template<typename IteratorTuple>
  class zip_iterator : 
    public detail::zip_iterator_base<IteratorTuple>::type
  {  

   // Typedef super_t as our base class. 
   typedef typename 
     detail::zip_iterator_base<IteratorTuple>::type super_t;

   // iterator_core_access is the iterator's best friend.
   friend class iterator_core_access;

  public:
    
    // Construction
    // ============
    
    // Default constructor
    zip_iterator() { }

    // Constructor from iterator tuple
    zip_iterator(IteratorTuple iterator_tuple) 
      : m_iterator_tuple(iterator_tuple) 
    { }

    // Copy constructor
    template<typename OtherIteratorTuple>
    zip_iterator(
       const zip_iterator<OtherIteratorTuple>& other,
       typename enable_if_convertible<
         OtherIteratorTuple,
         IteratorTuple
         >::type* = 0
    ) : m_iterator_tuple(other.get_iterator_tuple())
    {}

    // Get method for the iterator tuple.
    const IteratorTuple& get_iterator_tuple() const
    { return m_iterator_tuple; }

  private:
    
    // Implementation of Iterator Operations
    // =====================================
    
    // Dereferencing returns a tuple built from the dereferenced
    // iterators in the iterator tuple.
    typename super_t::reference dereference() const
    { 
      return detail::tuple_impl_specific::tuple_transform( 
        get_iterator_tuple(),
        detail::dereference_iterator()
       );
    }

    // Two zip iterators are equal if all iterators in the iterator
    // tuple are equal. NOTE: It should be possible to implement this
    // as
    //
    // return get_iterator_tuple() == other.get_iterator_tuple();
    //
    // but equality of tuples currently (7/2003) does not compile
    // under several compilers. No point in bringing in a bunch
    // of #ifdefs here.
    //
    template<typename OtherIteratorTuple>   
    bool equal(const zip_iterator<OtherIteratorTuple>& other) const
    {
      return detail::tuple_impl_specific::tuple_equal(
        get_iterator_tuple(),
        other.get_iterator_tuple()
        );
    }

    // Advancing a zip iterator means to advance all iterators in the
    // iterator tuple.
    void advance(typename super_t::difference_type n)
    { 
      detail::tuple_impl_specific::tuple_for_each(
          m_iterator_tuple,
          detail::advance_iterator<BOOST_DEDUCED_TYPENAME super_t::difference_type>(n)
          );
    }
    // Incrementing a zip iterator means to increment all iterators in
    // the iterator tuple.
    void increment()
    { 
      detail::tuple_impl_specific::tuple_for_each(
        m_iterator_tuple,
        detail::increment_iterator()
        );
    }
    
    // Decrementing a zip iterator means to decrement all iterators in
    // the iterator tuple.
    void decrement()
    { 
      detail::tuple_impl_specific::tuple_for_each(
        m_iterator_tuple,
        detail::decrement_iterator()
        );
    }
    
    // Distance is calculated using the first iterator in the tuple.
    template<typename OtherIteratorTuple>
      typename super_t::difference_type distance_to(
        const zip_iterator<OtherIteratorTuple>& other
        ) const
    { 
        return boost::tuples::get<0>(other.get_iterator_tuple()) - 
            boost::tuples::get<0>(this->get_iterator_tuple());
    }
  
    // Data Members
    // ============
    
    // The iterator tuple.
    IteratorTuple m_iterator_tuple;
 
  };

  // Make function for zip iterator
  //
  template<typename IteratorTuple> 
  zip_iterator<IteratorTuple> 
  make_zip_iterator(IteratorTuple t)
  { return zip_iterator<IteratorTuple>(t); }

}

#endif