source: branches/0.6-stable/yat/utility/iterator_traits.h @ 2164

#ifndef _theplu_yat_utility_iterator_traits_
#define _theplu_yat_utility_iterator_traits_

// $Id: iterator_traits.h 2164 2010-01-20 05:01:55Z peter $

/*
  Copyright (C) 2007 Jari Häkkinen, Peter Johansson
  Copyright (C) 2008 Jari Häkkinen, Peter Johansson, Markus Ringnér
  Copyright (C) 2010 Peter Johansson

  This file is part of the yat library, http://dev.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 3 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 yat. If not, see <http://www.gnu.org/licenses/>.
*/

#include "DataWeight.h"

#include <boost/type_traits/is_convertible.hpp>
#include <boost/utility/enable_if.hpp>

#include <iterator>

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 {};


namespace detail {
  /**
     \internal

     used in weighted_iterator_traits
  */
  template <typename T, typename Enable = void>
  struct weighted_iterator_traits_detail {
    /**
       default is a iterator unweighted
    */
    typedef unweighted_iterator_tag type;
  };  

  /** 
      \internal

      specialization for iterators with value type DataWeight
  */
  template <typename T>
  struct weighted_iterator_traits_detail<T, typename boost::enable_if<typename boost::is_convertible<T, DataWeight>::type>::type > {
    /**
       Iterators with value type DataWeight is weighted
     */
    typedef weighted_iterator_tag type;
  };  

} // namespace detail


  /** 
      Metafunction to decide whether an Iterator is weighted or
      non-weighted. This (default) implementation returns
      unweighted_iterator_tag, unless \t value_type of Iterator is
      convertible to DataWeight in which case weighted_iterator_tag is
      returned.
  */
  template <class Iterator>
  struct weighted_iterator_traits 
  {
  private:
    typedef typename std::iterator_traits<T>::value_type value;
  public:
    /**
       \return weighted if value_type is DataWeight
     */
    typedef typename detail::weighted_iterator_traits_detail<value>::type type;
  };


namespace detail {
  /**
     \internal

    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 {
    /**
       default return weighted_iterator_tag
     */
    typedef weighted_iterator_tag type;
  };

  /**
     \internal

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

  /**
    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 {
  private:
    typedef typename weighted_iterator_traits<T1>::type w_type1;
    typedef typename weighted_iterator_traits<T2>::type w_type2;
  public:
    /// return unweighted if both are unweighted
    typedef typename detail::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 {
  private:
    typedef typename weighted_if_any2<T1, T2>::type tmp;
    typedef typename weighted_iterator_traits<T3>::type w_type3;
  public:
    /// return unweighted if all are unweighted
    typedef typename detail::unweighted_type_and<tmp, w_type3>::type type;
  };

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

  /**
     \brief check (at compile time) that iterator is unweighted.

     This function only compiles if iterator \a iter is unweighted.
   */
  template <class Iter>
  void check_iterator_is_unweighted(Iter iter) 
  { detail::check_iterator_is_unweighted(typename 
                                 weighted_iterator_traits<Iter>::type());
  }


namespace detail {
  /**
     \internal

     This class is used in iterator_traits to separate different cases. 

     This the default implementation that could be used for unweighted
     iterators.
   */
  template <typename Iter, typename T >
  struct iterator_traits_detail 
  {
    /**
       for unweighted data_reference is reference
    */
    typedef typename std::iterator_traits<Iter>::reference data_reference;

    /**
       for unweighted weight_reference is a double
    */
    typedef double weight_reference;

    /**
       Constructor just checking that iterator is unweighted
    */
    iterator_traits_detail(void) 
    { check_iterator_is_unweighted(typename 
                                   weighted_iterator_traits<Iter>::type());
    }
    
    /**
       \return * \a iter 
    */
    data_reference data(Iter iter) const { return *iter; }

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


  /**
     specialization for weighted iterator with reference DataWeight&
   */
  template <typename Iter>
  struct iterator_traits_detail<Iter, DataWeight&> {
    /**
       for mutable weighted iterator data_reference is double&
    */
    typedef double& data_reference;

    /**
       for mutable weighted iterator weight_reference is double&
    */
    typedef double& weight_reference;

    /**
       \return reference to data of iterator
    */
    data_reference data(Iter iter) const { return (*iter).data(); }

    /**
       \return reference to weight of iterator
    */
    weight_reference weight(Iter iter) const { return (*iter).weight(); }
  };


  /**
     specialization for weighted iterator with reference const DataWeight&
   */
  template <typename Iter>
  struct iterator_traits_detail<Iter, const DataWeight&> {
    /**
       for read-only weighted iterator data_reference is const double&
    */
    typedef const double& data_reference;

    /**
       for read-only weighted iterator data_reference is const double&
    */
    typedef const double& weight_reference;

    /**
       \return const reference to data of iterator
    */
    data_reference data(Iter iter) const { return (*iter).data(); }

    /**
       \return const reference to weight of iterator
    */
    weight_reference weight(Iter iter) const { return (*iter).weight(); }
  };


  /**
     specialization for weighted iterator with reference const DataWeight
   */
  template <typename Iter>
  struct iterator_traits_detail<Iter, const DataWeight> {
    /**
       \brief data_reference
    */
    typedef const double data_reference;

    /**
       \brief weight_reference
    */
    typedef const double weight_reference;

    /**
       \return const reference to data of iterator
    */
    data_reference data(Iter iter) const { return (*iter).data(); }

    /**
       \return const reference to weight of iterator
    */
    weight_reference weight(Iter iter) const { return (*iter).weight(); }
  };
} // namespace detail

  /**
     The purpose of this class is to allow polymorphism between
     weighted and unweighted iterators. It allows to access data and
     weight for both weighted and unweighted iterators.

     This class works for unweighted iterators as well as weighted
     iterators as long as they have reference type DataWeight& or
     const DataWeight&.

     For others, such as WeightedIterator for which reference type is
     a proxy class, this class should be specialized. For adaptors
     that have an underlying iterator (e.g. StrideIterator), this
     class should be specialized, so the class also works when the
     underlying is an iterator that is not covered by this class
     e.g. WeightedIterator.
   */ 
  template <typename Iter>
  struct iterator_traits {
  private:
    typedef typename std::iterator_traits<Iter>::reference reference;
    typedef detail::iterator_traits_detail<Iter, reference> traits;
  public:
    /**
       data_reference (type returned by data(void) is determined by
       iterator_traits_detail
     */
    typedef typename traits::data_reference data_reference;

    /**
       data_reference (type returned by data(void) is determined by
       iterator_traits_detail
     */
    typedef typename traits::weight_reference weight_reference;

    /**
       \return data
    */
    data_reference data(Iter iter) const 
    { return traits().data(iter); }

    /**
       \return weight
     */
    weight_reference weight(Iter iter) const 
    { return traits().weight(iter); }

  };


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

#endif