source: trunk/yat/utility/iterator_traits.h @ 958

Last change on this file since 958 was 958, checked in by Peter, 14 years ago

allowing mixture of weighted and unweighted iterators in vector_distance

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1#ifndef _theplu_yat_utility_iterator_traits_
2#define _theplu_yat_utility_iterator_traits_
3
4// $Id: iterator_traits.h 958 2007-10-10 15:44:06Z peter $
5
6/*
7  Copyright (C) 2007 Peter Johansson
8
9  This file is part of the yat library, http://trac.thep.lu.se/trac/yat
10
11  The yat library is free software; you can redistribute it and/or
12  modify it under the terms of the GNU General Public License as
13  published by the Free Software Foundation; either version 2 of the
14  License, or (at your option) any later version.
15
16  The yat library is distributed in the hope that it will be useful,
17  but WITHOUT ANY WARRANTY; without even the implied warranty of
18  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19  General Public License for more details.
20
21  You should have received a copy of the GNU General Public License
22  along with this program; if not, write to the Free Software
23  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
24  02111-1307, USA.
25*/
26
27#include "yat/utility/IteratorWeighted.h"
28
29namespace theplu {
30namespace yat {
31namespace utility {
32
33  /*
34    Struct to be used to make compile-time decision that Iterator is
35    unweighted, which is the default.
36   */ 
37  struct unweighted_type {
38    typedef unweighted_type type;
39  };
40   
41  /*
42    Struct to be used to make compile-time decision that Iterator is
43    weighted. Some algorithms come in also in a weighted version in
44    this tag could be used to decide on using them (rather than
45    unweighted cousin).
46   */ 
47  struct weighted_type {
48    typedef weighted_type type;
49  };
50
51  // All iterators should default to unweighted type ...
52  template <class T>
53  struct weighted_iterator_traits {
54    typedef unweighted_type type;
55  };
56
57  // but specialized to return weighted type for some things
58  //
59  // if you add a new weighted iterator, add a new specialization like
60  // this one.
61  template <class U, class V>
62  struct weighted_iterator_traits<yat::utility::IteratorWeighted<U,V> > {
63    typedef weighted_type type;
64  };
65
66
67
68  /*
69    Metafunction that works on a pair weighted-unweighted types and
70    return weighted_type. The metafunction is specialized for
71    unweighted unweighted in which case unweighted is returned.
72   */
73  template <class T1, class T2>
74  struct unweighted_type_and {
75    typedef weighted_type type;
76  };
77
78  /*
79    Specialization that sets type to be unweighted when both arguments
80    are unweighted
81   */
82  template <>
83  struct unweighted_type_and<unweighted_type, unweighted_type> {
84    typedef unweighted_type type;
85  };
86
87  /*
88    struct used to determine if a pair of iterators should be treated
89    as weighted. If both iterators are unweighted, type is set to
90    unweighted else weighted.
91  */
92  template <class T1, class T2>
93  struct weighted_if_any2 {
94    typedef typename weighted_iterator_traits<T1>::type w_type1;
95    typedef typename weighted_iterator_traits<T2>::type w_type2;
96    typedef typename unweighted_type_and<w_type1, w_type2>::type type;
97  };
98
99  /*
100    Same as weighted_iterator_traits2 but for 3 arguments.
101   */
102  template <class T1, class T2, class T3>
103  struct weighted_if_any3 {
104    typedef typename weighted_if_any2<T1, T2>::type tmp;
105    typedef typename weighted_iterator_traits<T3>::type w_type3;
106    typedef typename unweighted_type_and<tmp, w_type3>::type type;
107  };
108
109  // check (at compile time) that iterator is unweighted.
110  inline void check_iterator_is_unweighted(unweighted_type x){} 
111  template <class Iter>
112  void check_iterator_is_unweighted(Iter iter) 
113  { check_iterator_is_unweighted(typename 
114                                 weighted_iterator_traits<Iter>::type());
115  }
116
117
118  /*
119    Function to be used to make compile-time decision how to return
120    data from an iterator separating two cases: weighted and
121    unweighted.
122
123    In this way unweighted iterators can be used in a weighted context.
124   */ 
125  // Peter, perhaps these should be templatized, but for now return
126  // type double is hard coded.
127  template <class Iter>
128  double iterator_traits_data(Iter iter)
129  { return iterator_traits_data(iter, typename 
130                                weighted_iterator_traits<Iter>::type()); } 
131
132  template <class Iter>
133  double iterator_traits_data(Iter i, weighted_type)
134  { return i.data(); } 
135
136  template <class Iter>
137  double iterator_traits_data(Iter i, unweighted_type)
138  { return *i; } 
139
140  /*
141    Function to be used to make compile-time decision how to return
142    data from an iterator separating two cases: weighted and
143    unweighted.
144
145    In this way unweighted iterators can be used in a weighted context
146    and weight will be set to unity.
147   */ 
148  // Peter, perhaps these should be templatized, but for now return
149  // type double is hard coded.
150  template <class Iter>
151  double iterator_traits_weight(Iter iter)
152  { return iterator_traits_weight(iter, typename 
153                                  weighted_iterator_traits<Iter>::type()); } 
154
155  template <class Iter>
156  double iterator_traits_weight(Iter i, weighted_type)
157  { return i.weight(); } 
158
159  template <class Iter>
160  double iterator_traits_weight(Iter i, unweighted_type)
161  { return 1.0; } 
162
163
164}}} // of namespace utility, yat, and theplu
165
166#endif
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