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<div class="titlepage"><div><div><h4 class="title">
<a name="geometry.reference.core.tag_cast"></a><a class="link" href="tag_cast.html" title="tag_cast">tag_cast</a>
</h4></div></div></div>
<p>
<a class="indexterm" name="id928686"></a>
Metafunction defining a type being either the specified tag, or one of
the specified basetags if the type inherits from them.
</p>
<a name="geometry.reference.core.tag_cast.description"></a><h6>
<a name="geometry.reference.core.tag_cast.description-heading"></a>
<a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.description">Description</a>
</h6>
<p>
Tags can inherit each other. A multi_point inherits, for example, both
the multi_tag and the pointlike tag. Often behaviour can be shared between
different geometry types. A tag, found by the metafunction tag, can be
casted to a more basic tag, and then dispatched by that tag.
</p>
<a name="geometry.reference.core.tag_cast.synopsis"></a><h6>
<a name="geometry.reference.core.tag_cast.synopsis-heading"></a>
<a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.synopsis">Synopsis</a>
</h6>
<p>
</p>
<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> <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>
<span class="keyword">struct</span> <span class="identifier">tag_cast</span>
<span class="special">{</span>
<span class="comment">// ...</span>
<span class="special">};</span>
</pre>
<p>
</p>
<a name="geometry.reference.core.tag_cast.template_parameter_s_"></a><h6>
<a name="geometry.reference.core.tag_cast.template_parameter_s_-heading"></a>
<a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.template_parameter_s_">Template
parameter(s)</a>
</h6>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Parameter
</p>
</th>
<th>
<p>
Default
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
typename Tag
</p>
</td>
<td>
</td>
<td>
<p>
The tag to be casted to one of the base tags
</p>
</td>
</tr>
<tr>
<td>
<p>
typename BaseTag
</p>
</td>
<td>
</td>
<td>
<p>
First base tag
</p>
</td>
</tr>
<tr>
<td>
<p>
typename BaseTag2
</p>
</td>
<td>
<p>
void
</p>
</td>
<td>
<p>
Optional second base tag
</p>
</td>
</tr>
<tr>
<td>
<p>
typename BaseTag3
</p>
</td>
<td>
<p>
void
</p>
</td>
<td>
<p>
Optional third base tag
</p>
</td>
</tr>
<tr>
<td>
<p>
typename BaseTag4
</p>
</td>
<td>
<p>
void
</p>
</td>
<td>
<p>
Optional fourth base tag
</p>
</td>
</tr>
<tr>
<td>
<p>
typename BaseTag5
</p>
</td>
<td>
<p>
void
</p>
</td>
<td>
<p>
Optional fifth base tag
</p>
</td>
</tr>
<tr>
<td>
<p>
typename BaseTag6
</p>
</td>
<td>
<p>
void
</p>
</td>
<td>
<p>
Optional sixth base tag
</p>
</td>
</tr>
<tr>
<td>
<p>
typename BaseTag7
</p>
</td>
<td>
<p>
void
</p>
</td>
<td>
<p>
Optional seventh base tag
</p>
</td>
</tr>
</tbody>
</table></div>
<a name="geometry.reference.core.tag_cast.header"></a><h6>
<a name="geometry.reference.core.tag_cast.header-heading"></a>
<a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.header">Header</a>
</h6>
<p>
Either
</p>
<p>
<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">geometry</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span></code>
</p>
<p>
Or
</p>
<p>
<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>
</p>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
The specified tag list is handled in the specified order: as soon as
a tag inheriting the specified tag is found, it is defined as the metafunction
typedef <span class="bold"><strong>type</strong></span>.
</p></td></tr>
</table></div>
<div class="note"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top"><p>
If none of the specified possible base tags is a base class of the specified
tag, the tag itself is defined as the <span class="bold"><strong>type</strong></span>
result of the metafunction.
</p></td></tr>
</table></div>
<a name="geometry.reference.core.tag_cast.complexity"></a><h6>
<a name="geometry.reference.core.tag_cast.complexity-heading"></a>
<a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.complexity">Complexity</a>
</h6>
<p>
Compile time
</p>
<a name="geometry.reference.core.tag_cast.example"></a><h6>
<a name="geometry.reference.core.tag_cast.example-heading"></a>
<a class="link" href="tag_cast.html#geometry.reference.core.tag_cast.example">Example</a>
</h6>
<p>
Check if the polygon_tag can be casted to the areal_tag
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">typeinfo</span><span class="special">&gt;</span>
<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>
<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>
<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>
<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>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<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>
<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>
<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>
<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>
<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>
<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>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
<p>
Output (in MSVC):
</p>
<pre class="programlisting">tag: struct boost::geometry::polygon_tag
base tag: struct boost::geometry::areal_tag
</pre>
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<td align="right"><div class="copyright-footer">Copyright &#169; 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>)
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