1 // Boost.Geometry (aka GGL, Generic Geometry Library)
2 
3 // Copyright (c) 2007-2012 Barend Gehrels, Amsterdam, the Netherlands.
4 // Copyright (c) 2008-2012 Bruno Lalande, Paris, France.
5 // Copyright (c) 2009-2012 Mateusz Loskot, London, UK.
6 
7 // Parts of Boost.Geometry are redesigned from Geodan's Geographic Library
8 // (geolib/GGL), copyright (c) 1995-2010 Geodan, Amsterdam, the Netherlands.
9 
10 // Use, modification and distribution is subject to the Boost Software License,
11 // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
12 // http://www.boost.org/LICENSE_1_0.txt)
13 
14 
15 #ifndef BOOST_GEOMETRY_STRATEGIES_COMPARE_HPP
16 #define BOOST_GEOMETRY_STRATEGIES_COMPARE_HPP
17 
18 #include <cstddef>
19 #include <functional>
20 
21 #include <boost/mpl/if.hpp>
22 
23 #include <boost/geometry/core/cs.hpp>
24 #include <boost/geometry/core/coordinate_type.hpp>
25 
26 #include <boost/geometry/strategies/tags.hpp>
27 
28 
29 namespace boost { namespace geometry
30 {
31 
32 
33 /*!
34     \brief Traits class binding a comparing strategy to a coordinate system
35     \ingroup util
36     \tparam Tag tag of coordinate system of point-type
37     \tparam Direction direction to compare on: 1 for less (-> ascending order)
38         and -1 for greater (-> descending order)
39     \tparam Point point-type
40     \tparam CoordinateSystem coordinate sytem of point
41     \tparam Dimension: the dimension to compare on
42 */
43 template
44 <
45     typename Tag,
46     int Direction,
47     typename Point,
48     typename CoordinateSystem,
49     std::size_t Dimension
50 >
51 struct strategy_compare
52 {
53     typedef strategy::not_implemented type;
54 };
55 
56 
57 #ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
58 
59 // For compare we add defaults specializations,
60 // because they defaultly redirect to std::less / greater / equal_to
61 template
62 <
63     typename Tag,
64     typename Point,
65     typename CoordinateSystem,
66     std::size_t Dimension
67 >
68 struct strategy_compare<Tag, 1, Point, CoordinateSystem, Dimension>
69 {
70     typedef std::less<typename coordinate_type<Point>::type> type;
71 };
72 
73 
74 template
75 <
76     typename Tag,
77     typename Point,
78     typename CoordinateSystem,
79     std::size_t Dimension
80 >
81 struct strategy_compare<Tag, -1, Point, CoordinateSystem, Dimension>
82 {
83     typedef std::greater<typename coordinate_type<Point>::type> type;
84 };
85 
86 
87 template
88 <
89     typename Tag,
90     typename Point,
91     typename CoordinateSystem,
92     std::size_t Dimension
93 >
94 struct strategy_compare<Tag, 0, Point, CoordinateSystem, Dimension>
95 {
96     typedef std::equal_to<typename coordinate_type<Point>::type> type;
97 };
98 
99 
100 #endif
101 
102 
103 namespace strategy { namespace compare
104 {
105 
106 
107 /*!
108     \brief Default strategy, indicates the default strategy for comparisons
109     \details The default strategy for comparisons defer in most cases
110         to std::less (for ascending) and std::greater (for descending).
111         However, if a spherical coordinate system is used, and comparison
112         is done on longitude, it will take another strategy handling circular
113 */
114 struct default_strategy {};
115 
116 
117 #ifndef DOXYGEN_NO_DETAIL
118 namespace detail
119 {
120 
121 template <typename Type>
122 struct is_default : boost::false_type
123 {};
124 
125 
126 template <>
127 struct is_default<default_strategy> : boost::true_type
128 {};
129 
130 
131 /*!
132     \brief Meta-function to select strategy
133     \details If "default_strategy" is specified, it will take the
134         traits-registered class for the specified coordinate system.
135         If another strategy is explicitly specified, it takes that one.
136 */
137 template
138 <
139     typename Strategy,
140     int Direction,
141     typename Point,
142     std::size_t Dimension
143 >
144 struct select_strategy
145 {
146     typedef typename
147         boost::mpl::if_
148         <
149             is_default<Strategy>,
150             typename strategy_compare
151             <
152                 typename cs_tag<Point>::type,
153                 Direction,
154                 Point,
155                 typename coordinate_system<Point>::type,
156                 Dimension
157             >::type,
158             Strategy
159         >::type type;
160 };
161 
162 } // namespace detail
163 #endif // DOXYGEN_NO_DETAIL
164 
165 
166 }} // namespace strategy::compare
167 
168 
169 }} // namespace boost::geometry
170 
171 
172 #endif // BOOST_GEOMETRY_STRATEGIES_COMPARE_HPP
173