libs/geometry/doc/html/geometry/reference/core/tag.html

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  25 <div class="section">
  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="geometry.reference.core.tag"></a><a class="link" href="tag.html" title="tag">tag</a>
  28 </h4></div></div></div>
  29 <p>
  30           <a class="indexterm" name="idp125018304"></a>
  31 Metafunction defining <span class="bold"><strong>type</strong></span> as the tag
  32           of the specified geometry type.
  33         </p>
  34 <h6>
  35 <a name="geometry.reference.core.tag.h0"></a>
  36           <span class="phrase"><a name="geometry.reference.core.tag.description"></a></span><a class="link" href="tag.html#geometry.reference.core.tag.description">Description</a>
  37         </h6>
  38 <p>
  39           With Boost.Geometry, tags are the driving force of the tag dispatching
  40           mechanism. The tag metafunction is therefore used in every free function.
  41         </p>
  42 <h6>
  43 <a name="geometry.reference.core.tag.h1"></a>
  44           <span class="phrase"><a name="geometry.reference.core.tag.synopsis"></a></span><a class="link" href="tag.html#geometry.reference.core.tag.synopsis">Synopsis</a>
  45         </h6>
  46 <p>
  47 </p>
  48 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Geometry</span><span class="special">&gt;</span>
  49 <span class="keyword">struct</span> <span class="identifier">tag</span>
  50 <span class="special">{</span>
  51   <span class="comment">// ...</span>
  52 <span class="special">};</span>
  53 </pre>
  54 <p>
  55         </p>
  56 <h6>
  57 <a name="geometry.reference.core.tag.h2"></a>
  58           <span class="phrase"><a name="geometry.reference.core.tag.template_parameter_s_"></a></span><a class="link" href="tag.html#geometry.reference.core.tag.template_parameter_s_">Template
  59           parameter(s)</a>
  60         </h6>
  61 <div class="informaltable"><table class="table">
  62 <colgroup>
  63 <col>
  64 <col>
  65 </colgroup>
  66 <thead><tr>
  67 <th>
  68                   <p>
  69                     Parameter
  70                   </p>
  71                 </th>
  72 <th>
  73                   <p>
  74                     Description
  75                   </p>
  76                 </th>
  77 </tr></thead>
  78 <tbody><tr>
  79 <td>
  80                   <p>
  81                     typename Geometry
  82                   </p>
  83                 </td>
  84 <td>
  85                   <p>
  86                     Any type fulfilling a Geometry Concept
  87                   </p>
  88                 </td>
  89 </tr></tbody>
  90 </table></div>
  91 <h6>
  92 <a name="geometry.reference.core.tag.h3"></a>
  93           <span class="phrase"><a name="geometry.reference.core.tag.header"></a></span><a class="link" href="tag.html#geometry.reference.core.tag.header">Header</a>
  94         </h6>
  95 <p>
  96           Either
  97         </p>
  98 <p>
  99           <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
 100         </p>
 101 <p>
 102           Or
 103         </p>
 104 <p>
 105           <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">core</span><span class="special">/</span><span class="identifier">tag</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
 106         </p>
 107 <h6>
 108 <a name="geometry.reference.core.tag.h4"></a>
 109           <span class="phrase"><a name="geometry.reference.core.tag.metafunction_result_type"></a></span><a class="link" href="tag.html#geometry.reference.core.tag.metafunction_result_type">Metafunction
 110           result type</a>
 111         </h6>
 112 <p>
 113           The metafunction tag defines <span class="bold"><strong>type</strong></span> as one
 114           of the following tags:
 115         </p>
 116 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 117 <li class="listitem">
 118               point_tag
 119             </li>
 120 <li class="listitem">
 121               linestring_tag
 122             </li>
 123 <li class="listitem">
 124               polygon_tag
 125             </li>
 126 <li class="listitem">
 127               multi_point_tag
 128             </li>
 129 <li class="listitem">
 130               multi_linestring_tag
 131             </li>
 132 <li class="listitem">
 133               multi_polygon_tag
 134             </li>
 135 <li class="listitem">
 136               box_tag
 137             </li>
 138 <li class="listitem">
 139               segment_tag
 140             </li>
 141 <li class="listitem">
 142               ring_tag
 143             </li>
 144 </ul></div>
 145 <h6>
 146 <a name="geometry.reference.core.tag.h5"></a>
 147           <span class="phrase"><a name="geometry.reference.core.tag.complexity"></a></span><a class="link" href="tag.html#geometry.reference.core.tag.complexity">Complexity</a>
 148         </h6>
 149 <p>
 150           Compile time
 151         </p>
 152 <h6>
 153 <a name="geometry.reference.core.tag.h6"></a>
 154           <span class="phrase"><a name="geometry.reference.core.tag.example"></a></span><a class="link" href="tag.html#geometry.reference.core.tag.example">Example</a>
 155         </h6>
 156 <p>
 157           Shows how tag dispatching essentially works in Boost.Geometry
 158         </p>
 159 <p>
 160 </p>
 161 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 162
 163 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">assign</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 164
 165 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 166 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">polygon</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 167 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">multi_polygon</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 168 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometries</span><span class="special">/</span><span class="identifier">adapted</span><span class="special">/</span><span class="identifier">boost_tuple</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 169
 170 <span class="identifier">BOOST_GEOMETRY_REGISTER_BOOST_TUPLE_CS</span><span class="special">(</span><span class="identifier">cs</span><span class="special">::</span><span class="identifier">cartesian</span><span class="special">)</span>
 171
 172 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Tag</span><span class="special">&gt;</span> <span class="keyword">struct</span> <span class="identifier">dispatch</span> <span class="special">{};</span>
 173
 174 <span class="comment">// Specialization for points</span>
 175 <span class="keyword">template</span> <span class="special">&lt;&gt;</span> <span class="keyword">struct</span> <span class="identifier">dispatch</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">point_tag</span><span class="special">&gt;</span>
 176 <span class="special">{</span>
 177     <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Point</span><span class="special">&gt;</span>
 178     <span class="keyword">static</span> <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">apply</span><span class="special">(</span><span class="identifier">Point</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">p</span><span class="special">)</span>
 179     <span class="special">{</span>
 180         <span class="comment">// Use the Boost.Geometry free function "get"</span>
 181         <span class="comment">// working on all supported point types</span>
 182         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Hello POINT, you are located at: "</span>
 183             <span class="special">&lt;&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">0</span><span class="special">&gt;(</span><span class="identifier">p</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="string">", "</span>
 184             <span class="special">&lt;&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">get</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;(</span><span class="identifier">p</span><span class="special">)</span>
 185             <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 186     <span class="special">}</span>
 187 <span class="special">};</span>
 188
 189 <span class="comment">// Specialization for polygons</span>
 190 <span class="keyword">template</span> <span class="special">&lt;&gt;</span> <span class="keyword">struct</span> <span class="identifier">dispatch</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">polygon_tag</span><span class="special">&gt;</span>
 191 <span class="special">{</span>
 192     <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Polygon</span><span class="special">&gt;</span>
 193     <span class="keyword">static</span> <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">apply</span><span class="special">(</span><span class="identifier">Polygon</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">p</span><span class="special">)</span>
 194     <span class="special">{</span>
 195         <span class="comment">// Use the Boost.Geometry manipulator "dsv"</span>
 196         <span class="comment">// working on all supported geometries</span>
 197         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Hello POLYGON, you look like: "</span>
 198             <span class="special">&lt;&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">dsv</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span>
 199             <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 200     <span class="special">}</span>
 201 <span class="special">};</span>
 202
 203 <span class="comment">// Specialization for multipolygons</span>
 204 <span class="keyword">template</span> <span class="special">&lt;&gt;</span> <span class="keyword">struct</span> <span class="identifier">dispatch</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">multi_polygon_tag</span><span class="special">&gt;</span>
 205 <span class="special">{</span>
 206     <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">MultiPolygon</span><span class="special">&gt;</span>
 207     <span class="keyword">static</span> <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">apply</span><span class="special">(</span><span class="identifier">MultiPolygon</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">m</span><span class="special">)</span>
 208     <span class="special">{</span>
 209         <span class="comment">// Use the Boost.Range free function "size" because all</span>
 210         <span class="comment">// multigeometries comply to Boost.Range</span>
 211         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Hello MULTIPOLYGON, you contain: "</span>
 212             <span class="special">&lt;&lt;</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span><span class="special">(</span><span class="identifier">m</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="string">" polygon(s)"</span>
 213             <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 214     <span class="special">}</span>
 215 <span class="special">};</span>
 216
 217 <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Geometry</span><span class="special">&gt;</span>
 218 <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">hello</span><span class="special">(</span><span class="identifier">Geometry</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">geometry</span><span class="special">)</span>
 219 <span class="special">{</span>
 220     <span class="comment">// Call the metafunction "tag" to dispatch, and call method (here "apply")</span>
 221     <span class="identifier">dispatch</span>
 222         <span class="special">&lt;</span>
 223             <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">tag</span><span class="special">&lt;</span><span class="identifier">Geometry</span><span class="special">&gt;::</span><span class="identifier">type</span>
 224         <span class="special">&gt;::</span><span class="identifier">apply</span><span class="special">(</span><span class="identifier">geometry</span><span class="special">);</span>
 225 <span class="special">}</span>
 226
 227 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
 228 <span class="special">{</span>
 229     <span class="comment">// Define polygon type (here: based on a Boost.Tuple)</span>
 230     <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">polygon</span><span class="special">&lt;</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">tuple</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">polygon_type</span><span class="special">;</span>
 231
 232     <span class="comment">// Declare and fill a polygon and a multipolygon</span>
 233     <span class="identifier">polygon_type</span> <span class="identifier">poly</span><span class="special">;</span>
 234     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">exterior_ring</span><span class="special">(</span><span class="identifier">poly</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">assign</span><span class="special">::</span><span class="identifier">tuple_list_of</span><span class="special">(</span><span class="number">0</span><span class="special">,</span> <span class="number">0</span><span class="special">)(</span><span class="number">0</span><span class="special">,</span> <span class="number">10</span><span class="special">)(</span><span class="number">10</span><span class="special">,</span> <span class="number">5</span><span class="special">)(</span><span class="number">0</span><span class="special">,</span> <span class="number">0</span><span class="special">);</span>
 235
 236     <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">multi_polygon</span><span class="special">&lt;</span><span class="identifier">polygon_type</span><span class="special">&gt;</span> <span class="identifier">multi</span><span class="special">;</span>
 237     <span class="identifier">multi</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">poly</span><span class="special">);</span>
 238
 239     <span class="comment">// Call "hello" for point, polygon, multipolygon</span>
 240     <span class="identifier">hello</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_tuple</span><span class="special">(</span><span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">));</span>
 241     <span class="identifier">hello</span><span class="special">(</span><span class="identifier">poly</span><span class="special">);</span>
 242     <span class="identifier">hello</span><span class="special">(</span><span class="identifier">multi</span><span class="special">);</span>
 243
 244     <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 245 <span class="special">}</span>
 246 </pre>
 247 <p>
 248         </p>
 249 <p>
 250           Output:
 251         </p>
 252 <pre class="programlisting">Hello POINT, you are located at: 2, 3
 253 Hello POLYGON, you look like: (((0, 0), (0, 10), (10, 5), (0, 0)))
 254 Hello MULTIPOLYGON, you contain: 1 polygon(s)
 255 </pre>
 256 </div>
 257 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 258 <td align="left"></td>
 259 <td align="right"><div class="copyright-footer">Copyright &#169; 2009-2014 Barend Gehrels, Bruno Lalande, Mateusz Loskot, Adam
 260       Wulkiewicz, Oracle and/or its affiliates<p>
 261         Distributed under the Boost Software License, Version 1.0. (See accompanying
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