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| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="geometry.reference.core.tag"></a><a class="link" href="tag.html" title="tag">tag</a> |
| </h4></div></div></div> |
| <p> |
| <a class="indexterm" name="id926261"></a> |
| Metafunction defining <span class="bold"><strong>type</strong></span> as the tag |
| of the specified geometry type. |
| </p> |
| <a name="geometry.reference.core.tag.description"></a><h6> |
| <a name="geometry.reference.core.tag.description-heading"></a> |
| <a class="link" href="tag.html#geometry.reference.core.tag.description">Description</a> |
| </h6> |
| <p> |
| With Boost.Geometry, tags are the driving force of the tag dispatching |
| mechanism. The tag metafunction is therefore used in every free function. |
| </p> |
| <a name="geometry.reference.core.tag.synopsis"></a><h6> |
| <a name="geometry.reference.core.tag.synopsis-heading"></a> |
| <a class="link" href="tag.html#geometry.reference.core.tag.synopsis">Synopsis</a> |
| </h6> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Geometry</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">tag</span> |
| <span class="special">{</span> |
| <span class="comment">// ...</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| </p> |
| <a name="geometry.reference.core.tag.template_parameter_s_"></a><h6> |
| <a name="geometry.reference.core.tag.template_parameter_s_-heading"></a> |
| <a class="link" href="tag.html#geometry.reference.core.tag.template_parameter_s_">Template |
| parameter(s)</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Parameter |
| </p> |
| </th> |
| <th> |
| <p> |
| Description |
| </p> |
| </th> |
| </tr></thead> |
| <tbody><tr> |
| <td> |
| <p> |
| typename Geometry |
| </p> |
| </td> |
| <td> |
| <p> |
| Any type fulfilling a Geometry Concept |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="geometry.reference.core.tag.header"></a><h6> |
| <a name="geometry.reference.core.tag.header-heading"></a> |
| <a class="link" href="tag.html#geometry.reference.core.tag.header">Header</a> |
| </h6> |
| <p> |
| Either |
| </p> |
| <p> |
| <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> |
| </p> |
| <p> |
| Or |
| </p> |
| <p> |
| <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special"><</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">></span></code> |
| </p> |
| <a name="geometry.reference.core.tag.metafunction_result_type"></a><h6> |
| <a name="geometry.reference.core.tag.metafunction_result_type-heading"></a> |
| <a class="link" href="tag.html#geometry.reference.core.tag.metafunction_result_type">Metafunction |
| result type</a> |
| </h6> |
| <p> |
| The metafunction tag defines <span class="bold"><strong>type</strong></span> as one |
| of the following tags: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| point_tag |
| </li> |
| <li class="listitem"> |
| linestring_tag |
| </li> |
| <li class="listitem"> |
| polygon_tag |
| </li> |
| <li class="listitem"> |
| multi_point_tag |
| </li> |
| <li class="listitem"> |
| multi_linestring_tag |
| </li> |
| <li class="listitem"> |
| multi_polygon_tag |
| </li> |
| <li class="listitem"> |
| box_tag |
| </li> |
| <li class="listitem"> |
| segment_tag |
| </li> |
| <li class="listitem"> |
| ring_tag |
| </li> |
| </ul></div> |
| <a name="geometry.reference.core.tag.complexity"></a><h6> |
| <a name="geometry.reference.core.tag.complexity-heading"></a> |
| <a class="link" href="tag.html#geometry.reference.core.tag.complexity">Complexity</a> |
| </h6> |
| <p> |
| Compile time |
| </p> |
| <a name="geometry.reference.core.tag.example"></a><h6> |
| <a name="geometry.reference.core.tag.example-heading"></a> |
| <a class="link" href="tag.html#geometry.reference.core.tag.example">Example</a> |
| </h6> |
| <p> |
| Shows how tag dispatching essentially works in Boost.Geometry |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> |
| |
| <span class="preprocessor">#include</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">hpp</span><span class="special">></span> |
| |
| <span class="preprocessor">#include</span> <span class="special"><</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">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</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">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">geometry</span><span class="special">/</span><span class="identifier">multi</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">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</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">></span> |
| |
| <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> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Tag</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">dispatch</span> <span class="special">{};</span> |
| |
| <span class="comment">// Specialization for points</span> |
| <span class="keyword">template</span> <span class="special"><></span> <span class="keyword">struct</span> <span class="identifier">dispatch</span><span class="special"><</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">></span> |
| <span class="special">{</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Point</span><span class="special">></span> |
| <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">&</span> <span class="identifier">p</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="comment">// Use the Boost.Geometry free function "get"</span> |
| <span class="comment">// working on all supported point types</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Hello POINT, you are located at: "</span> |
| <span class="special"><<</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"><</span><span class="number">0</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span> <span class="special"><<</span> <span class="string">", "</span> |
| <span class="special"><<</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"><</span><span class="number">1</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span> |
| <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="comment">// Specialization for polygons</span> |
| <span class="keyword">template</span> <span class="special"><></span> <span class="keyword">struct</span> <span class="identifier">dispatch</span><span class="special"><</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">></span> |
| <span class="special">{</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Polygon</span><span class="special">></span> |
| <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">&</span> <span class="identifier">p</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="comment">// Use the Boost.Geometry manipulator "dsv" </span> |
| <span class="comment">// working on all supported geometries</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Hello POLYGON, you look like: "</span> |
| <span class="special"><<</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> |
| <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="comment">// Specialization for multipolygons</span> |
| <span class="keyword">template</span> <span class="special"><></span> <span class="keyword">struct</span> <span class="identifier">dispatch</span><span class="special"><</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">></span> |
| <span class="special">{</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">MultiPolygon</span><span class="special">></span> |
| <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">&</span> <span class="identifier">m</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="comment">// Use the Boost.Range free function "size" because all</span> |
| <span class="comment">// multigeometries comply to Boost.Range</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Hello MULTIPOLYGON, you contain: "</span> |
| <span class="special"><<</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"><<</span> <span class="string">" polygon(s)"</span> |
| <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Geometry</span><span class="special">></span> |
| <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">&</span> <span class="identifier">geometry</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="comment">// Call the metafunction "tag" to dispatch, and call method (here "apply")</span> |
| <span class="identifier">dispatch</span> |
| <span class="special"><</span> |
| <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"><</span><span class="identifier">Geometry</span><span class="special">>::</span><span class="identifier">type</span> |
| <span class="special">>::</span><span class="identifier">apply</span><span class="special">(</span><span class="identifier">geometry</span><span class="special">);</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">// Define polygon type (here: based on a Boost.Tuple)</span> |
| <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"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">tuple</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">polygon_type</span><span class="special">;</span> |
| |
| <span class="comment">// Declare and fill a polygon and a multipolygon</span> |
| <span class="identifier">polygon_type</span> <span class="identifier">poly</span><span class="special">;</span> |
| <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> |
| |
| <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"><</span><span class="identifier">polygon_type</span><span class="special">></span> <span class="identifier">multi</span><span class="special">;</span> |
| <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> |
| |
| <span class="comment">// Call "hello" for point, polygon, multipolygon</span> |
| <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> |
| <span class="identifier">hello</span><span class="special">(</span><span class="identifier">poly</span><span class="special">);</span> |
| <span class="identifier">hello</span><span class="special">(</span><span class="identifier">multi</span><span class="special">);</span> |
| |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| </pre> |
| <p> |
| </p> |
| <p> |
| Output: |
| </p> |
| <pre class="programlisting">Hello POINT, you are located at: 2, 3 |
| Hello POLYGON, you look like: (((0, 0), (0, 10), (10, 5), (0, 0))) |
| Hello MULTIPOLYGON, you contain: 1 polygon(s) |
| </pre> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2011 Barend Gehrels, Bruno Lalande, Mateusz Loskot<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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