source: trunk/yat/utility/iterator_traits.h @ 1115

#ifndef _theplu_yat_utility_iterator_traits_
#define _theplu_yat_utility_iterator_traits_

// $Id: iterator_traits.h 1115 2008-02-21 19:20:59Z markus $

/*
  Copyright (C) 2007 Peter Johansson

  This file is part of the yat library, http://trac.thep.lu.se/yat

  The yat library is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 of the
  License, or (at your option) any later version.

  The yat library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
  02111-1307, USA.
*/

namespace theplu {
namespace yat {
namespace utility {

  /**
    Struct to be used to make compile-time decision that Iterator is
    unweighted, which is the default.
   */ 
  struct unweighted_iterator_tag {};
    
  /**
    Struct to be used to make compile-time decision that Iterator is
    weighted. Some algorithms come also in a weighted version and
    this tag could be used to decide on using them (rather than
    the corresponding unweighted algorithm).
   */ 
  struct weighted_iterator_tag {};

  /** 
      All iterators default to unweighted type

      \see Iterator and StrideIterator
  */
  template <class T>
  struct weighted_iterator_traits {
    typedef unweighted_iterator_tag type;
  };

  /**
    Metafunction that works on a pair weighted-unweighted types and
    return weighted_type. The metafunction is specialized for
    unweighted unweighted in which case unweighted is returned.
   */
  template <class T1, class T2>
  struct unweighted_type_and {
    typedef weighted_iterator_tag type;
  };

  /**
    Specialization that sets type to be unweighted when both arguments
    are unweighted
   */
  template <>
  struct unweighted_type_and<unweighted_iterator_tag, unweighted_iterator_tag> {
    typedef unweighted_iterator_tag type;
  };

  /**
    struct used to determine if a pair of iterators should be treated
    as weighted. If both iterators are unweighted, type is set to
    unweighted else weighted.
  */
  template <class T1, class T2>
  struct weighted_if_any2 {
    typedef typename weighted_iterator_traits<T1>::type w_type1;
    typedef typename weighted_iterator_traits<T2>::type w_type2;
    typedef typename unweighted_type_and<w_type1, w_type2>::type type;
  };

  /**
    Same as weighted_iterator_traits2 but for 3 arguments.
   */
  template <class T1, class T2, class T3>
  struct weighted_if_any3 {
    typedef typename weighted_if_any2<T1, T2>::type tmp;
    typedef typename weighted_iterator_traits<T3>::type w_type3;
    typedef typename unweighted_type_and<tmp, w_type3>::type type;
  };

  /// check (at compile time) that iterator is unweighted. 
  inline void check_iterator_is_unweighted(unweighted_iterator_tag x){} 

  /**
     check (at compile time) that iterator \a iter is unweighted. This
     function is strictly not needed, but exists only for convenience.
   */
  template <class Iter>
  void check_iterator_is_unweighted(Iter iter) 
  { check_iterator_is_unweighted(typename 
                                 weighted_iterator_traits<Iter>::type());
  }


  /**
     \brief traits to make unweighted iterator work as in a weighted

     This class must be implemented for every iterator that can be weighted.

     \see StrideIterator and Iterator
   */ 
  template <class Iter>
  struct iterator_traits {
    // Peter, perhaps these should be templatized, but for now return
    // type double is hard coded.
    /**
       \return data that is *iter
    */
    double data(Iter iter) const 
    { check_iterator_is_unweighted(iter); return *iter; }

    /**
       \return 1.0
    */
    double weight(Iter iter) const 
    { check_iterator_is_unweighted(iter); return 1.0; }

  };

}}} // of namespace utility, yat, and theplu

#endif