shadow_iterator.hpp

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// (C) Copyright Jeremy Siek 2001.
// 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 BOOST_SHADOW_ITERATOR_HPP
#define BOOST_SHADOW_ITERATOR_HPP

#include <boost/iterator_adaptors.hpp>
#include <boost/operators.hpp>

namespace boost {

  namespace detail {

    template <class A, class B, class D>
    class shadow_proxy
      : boost::operators< shadow_proxy<A,B,D> >
    {
      typedef shadow_proxy self;
    public:
      inline shadow_proxy(A aa, B bb) : a(aa), b(bb) { }
      inline shadow_proxy(const self& x) : a(x.a), b(x.b) { }
      template <class Self>
      inline shadow_proxy(Self x) : a(x.a), b(x.b) { }
      inline self& operator=(const self& x) { a = x.a; b = x.b; return *this; }
      inline self& operator++() { ++a; return *this; }
      inline self& operator--() { --a; return *this; }
      inline self& operator+=(const self& x) { a += x.a; return *this; }
      inline self& operator-=(const self& x) { a -= x.a; return *this; }
      inline self& operator*=(const self& x) { a *= x.a; return *this; }
      inline self& operator/=(const self& x) { a /= x.a; return *this; }
      inline self& operator%=(const self& x) { return *this; } // JGS
      inline self& operator&=(const self& x) { return *this; } // JGS
      inline self& operator|=(const self& x) { return *this; } // JGS
      inline self& operator^=(const self& x) { return *this; } // JGS
      inline friend D operator-(const self& x, const self& y) {
        return x.a - y.a;
      } 
      inline bool operator==(const self& x) const { return a == x.a;  }
      inline bool operator<(const self& x) const { return a < x.a;  }
      //  protected:
      A a;
      B b;
    };

    struct shadow_iterator_policies
    {
      template <typename iter_pair>
      void initialize(const iter_pair&) { }

      template <typename Iter>
      typename Iter::reference dereference(const Iter& i) const { 
        typedef typename Iter::reference R;
        return R(*i.base().first, *i.base().second); 
      }
      template <typename Iter>
      bool equal(const Iter& p1, const Iter& p2) const { 
        return p1.base().first == p2.base().first;  
      }
      template <typename Iter>
      void increment(Iter& i) { ++i.base().first; ++i.base().second; }

      template <typename Iter>
      void decrement(Iter& i) { --i.base().first; --i.base().second; }

      template <typename Iter>
      bool less(const Iter& x, const Iter& y) const { 
        return x.base().first < y.base().first;  
      }
      template <typename Iter>
      typename Iter::difference_type
      distance(const Iter& x, const Iter& y) const { 
        return y.base().first - x.base().first; 
      }
      template <typename D, typename Iter>
      void advance(Iter& p, D n) { p.base().first += n; p.base().second += n; }
    };

  } // namespace detail

  template <typename IterA, typename IterB>
  struct shadow_iterator_generator {
    
    // To use the iterator_adaptor we can't derive from
    // random_access_iterator because we don't have a real reference.
    // However, we want the STL algorithms to treat the shadow
    // iterator like a random access iterator.
    struct shadow_iterator_tag : public std::input_iterator_tag {
      operator std::random_access_iterator_tag() {
        return std::random_access_iterator_tag();
      };
    };
    typedef typename std::iterator_traits<IterA>::value_type Aval;
    typedef typename std::iterator_traits<IterB>::value_type Bval;
    typedef typename std::iterator_traits<IterA>::reference Aref;
    typedef typename std::iterator_traits<IterB>::reference Bref;
    typedef typename std::iterator_traits<IterA>::difference_type D;
    typedef detail::shadow_proxy<Aval,Bval,Aval> V;
    typedef detail::shadow_proxy<Aref,Bref,Aval> R;
    typedef iterator_adaptor< std::pair<IterA, IterB>,
                              detail::shadow_iterator_policies,
                              V, R, V*, shadow_iterator_tag,
                              D> type;
  };

  // short cut for creating a shadow iterator
  template <class IterA, class IterB>
  inline typename shadow_iterator_generator<IterA,IterB>::type
  make_shadow_iter(IterA a, IterB b) {
    typedef typename shadow_iterator_generator<IterA,IterB>::type Iter;
    return Iter(std::make_pair(a,b)); 
  }

  template <class Cmp>
  struct shadow_cmp {
    inline shadow_cmp(const Cmp& c) : cmp(c) { }
    template <class ShadowProxy1, class ShadowProxy2>
    inline bool operator()(const ShadowProxy1& x, const ShadowProxy2& y) const
    {
      return cmp(x.a, y.a);
    }
    Cmp cmp;
  };

} // namespace boost

namespace std {
  template <class A1, class B1, class D1,
            class A2, class B2, class D2>
  void swap(boost::detail::shadow_proxy<A1&,B1&,D1> x,
            boost::detail::shadow_proxy<A2&,B2&,D2> y)
  {
    std::swap(x.a, y.a);
    std::swap(x.b, y.b);
  }
}

#endif // BOOST_SHADOW_ITERATOR_HPP