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

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>tag_cast</title>
   5 <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
   6 <meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
   7 <link rel="home" href="../../../index.html" title="Chapter&#160;1.&#160;Geometry">
   8 <link rel="up" href="../core.html" title="Core Metafunctions">
   9 <link rel="prev" href="tag.html" title="tag">
  10 <link rel="next" href="../de9im.html" title="DE-9IM">
  11 </head>
  12 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  13 <table cellpadding="2" width="100%"><tr>
  14 <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
  15 <td align="center"><a href="../../../../../../../index.html">Home</a></td>
  16 <td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
  17 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  19 <td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
  20 </tr></table>
  21 <hr>
  22 <div class="spirit-nav">
  23 <a accesskey="p" href="tag.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../core.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../de9im.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="geometry.reference.core.tag_cast"></a><a class="link" href="tag_cast.html" title="tag_cast">tag_cast</a>
  28 </h4></div></div></div>
  29 <p>
  30           <a class="indexterm" name="idm46186985884752"></a>
  31 Metafunction defining a type being either the specified tag, or one of
  32           the specified basetags if the type inherits from them.
  33         </p>
  34 <h6>
  35 <a name="geometry.reference.core.tag_cast.h0"></a>
  36           <span class="phrase"><a name="geometry.reference.core.tag_cast.description"></a></span><a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.description">Description</a>
  37         </h6>
  38 <p>
  39           Tags can inherit each other. A multi_point inherits, for example, both
  40           the multi_tag and the pointlike_tag. Often behaviour can be shared between
  41           different geometry types. A tag, found by the metafunction tag, can be
  42           casted to a more basic tag, and then dispatched by that tag.
  43         </p>
  44 <h6>
  45 <a name="geometry.reference.core.tag_cast.h1"></a>
  46           <span class="phrase"><a name="geometry.reference.core.tag_cast.synopsis"></a></span><a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.synopsis">Synopsis</a>
  47         </h6>
  48 <p>
  49 </p>
  50 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Tag</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BaseTag</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BaseTag2</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BaseTag3</span><span class="special">,</span>
  51          <span class="keyword">typename</span> <span class="identifier">BaseTag4</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BaseTag5</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BaseTag6</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">BaseTag7</span><span class="special">&gt;</span>
  52 <span class="keyword">struct</span> <span class="identifier">tag_cast</span>
  53 <span class="special">{</span>
  54   <span class="comment">// ...</span>
  55 <span class="special">};</span>
  56 </pre>
  57 <p>
  58         </p>
  59 <h6>
  60 <a name="geometry.reference.core.tag_cast.h2"></a>
  61           <span class="phrase"><a name="geometry.reference.core.tag_cast.template_parameter_s_"></a></span><a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.template_parameter_s_">Template
  62           parameter(s)</a>
  63         </h6>
  64 <div class="informaltable"><table class="table">
  65 <colgroup>
  66 <col>
  67 <col>
  68 <col>
  69 </colgroup>
  70 <thead><tr>
  71 <th>
  72                   <p>
  73                     Parameter
  74                   </p>
  75                 </th>
  76 <th>
  77                   <p>
  78                     Default
  79                   </p>
  80                 </th>
  81 <th>
  82                   <p>
  83                     Description
  84                   </p>
  85                 </th>
  86 </tr></thead>
  87 <tbody>
  88 <tr>
  89 <td>
  90                   <p>
  91                     typename Tag
  92                   </p>
  93                 </td>
  94 <td>
  95                 </td>
  96 <td>
  97                   <p>
  98                     The tag to be casted to one of the base tags
  99                   </p>
 100                 </td>
 101 </tr>
 102 <tr>
 103 <td>
 104                   <p>
 105                     typename BaseTag
 106                   </p>
 107                 </td>
 108 <td>
 109                 </td>
 110 <td>
 111                   <p>
 112                     First base tag
 113                   </p>
 114                 </td>
 115 </tr>
 116 <tr>
 117 <td>
 118                   <p>
 119                     typename BaseTag2
 120                   </p>
 121                 </td>
 122 <td>
 123                   <p>
 124                     void
 125                   </p>
 126                 </td>
 127 <td>
 128                   <p>
 129                     Optional second base tag
 130                   </p>
 131                 </td>
 132 </tr>
 133 <tr>
 134 <td>
 135                   <p>
 136                     typename BaseTag3
 137                   </p>
 138                 </td>
 139 <td>
 140                   <p>
 141                     void
 142                   </p>
 143                 </td>
 144 <td>
 145                   <p>
 146                     Optional third base tag
 147                   </p>
 148                 </td>
 149 </tr>
 150 <tr>
 151 <td>
 152                   <p>
 153                     typename BaseTag4
 154                   </p>
 155                 </td>
 156 <td>
 157                   <p>
 158                     void
 159                   </p>
 160                 </td>
 161 <td>
 162                   <p>
 163                     Optional fourth base tag
 164                   </p>
 165                 </td>
 166 </tr>
 167 <tr>
 168 <td>
 169                   <p>
 170                     typename BaseTag5
 171                   </p>
 172                 </td>
 173 <td>
 174                   <p>
 175                     void
 176                   </p>
 177                 </td>
 178 <td>
 179                   <p>
 180                     Optional fifth base tag
 181                   </p>
 182                 </td>
 183 </tr>
 184 <tr>
 185 <td>
 186                   <p>
 187                     typename BaseTag6
 188                   </p>
 189                 </td>
 190 <td>
 191                   <p>
 192                     void
 193                   </p>
 194                 </td>
 195 <td>
 196                   <p>
 197                     Optional sixth base tag
 198                   </p>
 199                 </td>
 200 </tr>
 201 <tr>
 202 <td>
 203                   <p>
 204                     typename BaseTag7
 205                   </p>
 206                 </td>
 207 <td>
 208                   <p>
 209                     void
 210                   </p>
 211                 </td>
 212 <td>
 213                   <p>
 214                     Optional seventh base tag
 215                   </p>
 216                 </td>
 217 </tr>
 218 </tbody>
 219 </table></div>
 220 <h6>
 221 <a name="geometry.reference.core.tag_cast.h3"></a>
 222           <span class="phrase"><a name="geometry.reference.core.tag_cast.header"></a></span><a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.header">Header</a>
 223         </h6>
 224 <p>
 225           Either
 226         </p>
 227 <p>
 228           <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>
 229         </p>
 230 <p>
 231           Or
 232         </p>
 233 <p>
 234           <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_cast</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
 235         </p>
 236 <div class="note"><table border="0" summary="Note">
 237 <tr>
 238 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
 239 <th align="left">Note</th>
 240 </tr>
 241 <tr><td align="left" valign="top"><p>
 242             The specified tag list is handled in the specified order: as soon as
 243             a tag inheriting the specified tag is found, it is defined as the metafunction
 244             typedef <span class="bold"><strong>type</strong></span>.
 245           </p></td></tr>
 246 </table></div>
 247 <div class="note"><table border="0" summary="Note">
 248 <tr>
 249 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
 250 <th align="left">Note</th>
 251 </tr>
 252 <tr><td align="left" valign="top"><p>
 253             If none of the specified possible base tags is a base class of the specified
 254             tag, the tag itself is defined as the <span class="bold"><strong>type</strong></span>
 255             result of the metafunction.
 256           </p></td></tr>
 257 </table></div>
 258 <h6>
 259 <a name="geometry.reference.core.tag_cast.h4"></a>
 260           <span class="phrase"><a name="geometry.reference.core.tag_cast.complexity"></a></span><a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.complexity">Complexity</a>
 261         </h6>
 262 <p>
 263           Compile time
 264         </p>
 265 <h6>
 266 <a name="geometry.reference.core.tag_cast.h5"></a>
 267           <span class="phrase"><a name="geometry.reference.core.tag_cast.example"></a></span><a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.example">Example</a>
 268         </h6>
 269 <p>
 270           Check if the polygon_tag can be casted to the areal_tag
 271         </p>
 272 <p>
 273 </p>
 274 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 275 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">typeinfo</span><span class="special">&gt;</span>
 276
 277 <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>
 278 <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>
 279 <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">point_xy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 280
 281 <span class="keyword">namespace</span> <span class="identifier">geo</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">geometry</span><span class="special">;</span>
 282 <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
 283 <span class="special">{</span>
 284     <span class="keyword">typedef</span> <span class="identifier">geo</span><span class="special">::</span><span class="identifier">model</span><span class="special">::</span><span class="identifier">d2</span><span class="special">::</span><span class="identifier">point_xy</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">point_type</span><span class="special">;</span>
 285     <span class="keyword">typedef</span> <span class="identifier">geo</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">point_type</span><span class="special">&gt;</span> <span class="identifier">polygon_type</span><span class="special">;</span>
 286
 287     <span class="keyword">typedef</span> <span class="identifier">geo</span><span class="special">::</span><span class="identifier">tag</span><span class="special">&lt;</span><span class="identifier">polygon_type</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">tag</span><span class="special">;</span>
 288     <span class="keyword">typedef</span> <span class="identifier">geo</span><span class="special">::</span><span class="identifier">tag_cast</span><span class="special">&lt;</span><span class="identifier">tag</span><span class="special">,</span> <span class="identifier">geo</span><span class="special">::</span><span class="identifier">linear_tag</span><span class="special">,</span> <span class="identifier">geo</span><span class="special">::</span><span class="identifier">areal_tag</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">base_tag</span><span class="special">;</span>
 289
 290     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"tag: "</span> <span class="special">&lt;&lt;</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">tag</span><span class="special">).</span><span class="identifier">name</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span>
 291         <span class="special">&lt;&lt;</span> <span class="string">"base tag: "</span> <span class="special">&lt;&lt;</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">base_tag</span><span class="special">).</span><span class="identifier">name</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
 292
 293     <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
 294 <span class="special">}</span>
 295 </pre>
 296 <p>
 297         </p>
 298 <p>
 299           Output (in MSVC):
 300         </p>
 301 <pre class="programlisting">tag: struct boost::geometry::polygon_tag
 302 base tag: struct boost::geometry::areal_tag
 303 </pre>
 304 </div>
 305 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 306 <td align="left"></td>
 307 <td align="right"><div class="copyright-footer">Copyright &#169; 2009-2019 Barend Gehrels, Bruno Lalande, Mateusz Loskot, Adam
 308       Wulkiewicz, Oracle and/or its affiliates<p>
 309         Distributed under the Boost Software License, Version 1.0. (See accompanying
 310         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>)
 311       </p>
 312 </div></td>
 313 </tr></table>
 314 <hr>
 315 <div class="spirit-nav">
 316 <a accesskey="p" href="tag.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../core.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../de9im.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
 317 </div>
 318 </body>
 319 </html>