/Src/Dependencies/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 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/multi/geometries/multi_polygon.hpp>
 20#include <boost/geometry/geometries/adapted/boost_tuple.hpp>
 21
 22BOOST_GEOMETRY_REGISTER_BOOST_TUPLE_CS(cs::cartesian)
 23
 24template <typename Tag> struct dispatch {};
 25
 26// Specialization for points
 27template <> 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
 42template <> 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
 56template <> 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
 69template <typename Geometry>
 70inline 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
 79int 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/*`
103Output:
104[pre
105Hello POINT, you are located at: 2, 3
106Hello POLYGON, you look like: (((0, 0), (0, 10), (10, 5), (0, 0)))
107Hello MULTIPOLYGON, you contain: 1 polygon(s)
108]
109*/
110//]