ceph/src/boost/libs/geometry/doc/src/examples/core/tag.cpp

   1 // Boost.Geometry (aka GGL, Generic Geometry Library)
   2 // QuickBook Example
   3
   4 // Copyright (c) 2011-2012 Barend Gehrels, Amsterdam, the Netherlands.
   5
   6 // Use, modification and distribution is subject to the Boost Software License,
   7 // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   8 // http://www.boost.org/LICENSE_1_0.txt)
   9
  10 //[tag
  11 //` Shows how tag dispatching essentially works in Boost.Geometry
  12
  13 #include <iostream>
  14
  15 #include <boost/assign.hpp>
  16
  17 #include <boost/geometry.hpp>
  18 #include <boost/geometry/geometries/polygon.hpp>
  19 #include <boost/geometry/geometries/multi_polygon.hpp>
  20 #include <boost/geometry/geometries/adapted/boost_tuple.hpp>
  21
  22 BOOST_GEOMETRY_REGISTER_BOOST_TUPLE_CS(cs::cartesian)
  23
  24 template <typename Tag> struct dispatch {};
  25
  26 // Specialization for points
  27 template <> struct dispatch<boost::geometry::point_tag>
  28 {
  29     template <typename Point>
  30     static inline void apply(Point const& p)
  31     {
  32         // Use the Boost.Geometry free function "get"
  33         // working on all supported point types
  34         std::cout << "Hello POINT, you are located at: "
  35             << boost::geometry::get<0>(p) << ", "
  36             << boost::geometry::get<1>(p)
  37             << std::endl;
  38     }
  39 };
  40
  41 // Specialization for polygons
  42 template <> struct dispatch<boost::geometry::polygon_tag>
  43 {
  44     template <typename Polygon>
  45     static inline void apply(Polygon const& p)
  46     {
  47         // Use the Boost.Geometry manipulator "dsv"
  48         // working on all supported geometries
  49         std::cout << "Hello POLYGON, you look like: "
  50             << boost::geometry::dsv(p)
  51             << std::endl;
  52     }
  53 };
  54
  55 // Specialization for multipolygons
  56 template <> struct dispatch<boost::geometry::multi_polygon_tag>
  57 {
  58     template <typename MultiPolygon>
  59     static inline void apply(MultiPolygon const& m)
  60     {
  61         // Use the Boost.Range free function "size" because all
  62         // multigeometries comply to Boost.Range
  63         std::cout << "Hello MULTIPOLYGON, you contain: "
  64             << boost::size(m) << " polygon(s)"
  65             << std::endl;
  66     }
  67 };
  68
  69 template <typename Geometry>
  70 inline void hello(Geometry const& geometry)
  71 {
  72     // Call the metafunction "tag" to dispatch, and call method (here "apply")
  73     dispatch
  74         <
  75             typename boost::geometry::tag<Geometry>::type
  76         >::apply(geometry);
  77 }
  78
  79 int main()
  80 {
  81     // Define polygon type (here: based on a Boost.Tuple)
  82     typedef boost::geometry::model::polygon<boost::tuple<int, int> > polygon_type;
  83
  84     // Declare and fill a polygon and a multipolygon
  85     polygon_type poly;
  86     boost::geometry::exterior_ring(poly) = boost::assign::tuple_list_of(0, 0)(0, 10)(10, 5)(0, 0);
  87
  88     boost::geometry::model::multi_polygon<polygon_type> multi;
  89     multi.push_back(poly);
  90
  91     // Call "hello" for point, polygon, multipolygon
  92     hello(boost::make_tuple(2, 3));
  93     hello(poly);
  94     hello(multi);
  95
  96     return 0;
  97 }
  98
  99 //]
 100
 101 //[tag_output
 102 /*`
 103 Output:
 104 [pre
 105 Hello POINT, you are located at: 2, 3
 106 Hello POLYGON, you look like: (((0, 0), (0, 10), (10, 5), (0, 0)))
 107 Hello MULTIPOLYGON, you contain: 1 polygon(s)
 108 ]
 109 */
 110 //]