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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit.advanced.customize.attribute_as"></a><a class="link" href="attribute_as.html" title="Atomically Extract an Attribute Value from a Container (Karma)">Atomically |
| Extract an Attribute Value from a Container (Karma)</a> |
| </h4></div></div></div> |
| <a name="spirit.advanced.customize.attribute_as.attribute_as"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.attribute_as-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.attribute_as">attribute_as</a> |
| </h6> |
| <p> |
| <code class="computeroutput"><span class="identifier">attribute_as</span></code> atomically |
| extracts an instance of a type from another type. This customization point |
| is used by the <a class="link" href="../../karma/reference/directive/as.html" title="Generator Directives Forcing Atomic Extraction (as<T>, as_string[], as_wstring[])"><code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>[]</span></code></a> |
| directive. |
| </p> |
| <a name="spirit.advanced.customize.attribute_as.module_headers"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.module_headers-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.module_headers">Module |
| Headers</a> |
| </h6> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">home</span><span class="special">/</span><span class="identifier">support</span><span class="special">/</span><span class="identifier">attributes_fwd</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| </pre> |
| <p> |
| Also, see <a class="link" href="../../structure/include.html" title="Include">Include Structure</a>. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| This header file does not need to be included directly by any user program |
| as it is normally included by other Spirit header files relying on its |
| content. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.advanced.customize.attribute_as.namespace"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.namespace-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.namespace">Namespace</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup><col></colgroup> |
| <thead><tr><th> |
| <p> |
| Name |
| </p> |
| </th></tr></thead> |
| <tbody><tr><td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">traits</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <a name="spirit.advanced.customize.attribute_as.synopsis"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.synopsis-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.synopsis">Synopsis</a> |
| </h6> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Attribute</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Enable</span> <span class="special">=</span> <span class="keyword">void</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">attribute_as</span><span class="special">;</span> |
| </pre> |
| <a name="spirit.advanced.customize.attribute_as.template_parameters"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.template_parameters-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.template_parameters">Template |
| parameters</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Parameter |
| </p> |
| </th> |
| <th> |
| <p> |
| Description |
| </p> |
| </th> |
| <th> |
| <p> |
| Default |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">T</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The type of the attribute natively exposed by the component the |
| <code class="computeroutput"><span class="identifier">attribute_as</span></code> |
| is invoked from. |
| </p> |
| </td> |
| <td> |
| <p> |
| none |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Attribute</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The type of the attribute to be used to generate output from. |
| </p> |
| </td> |
| <td> |
| <p> |
| none |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Enable</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Helper template parameter usable to selectively enable or disable |
| certain specializations of <code class="computeroutput"><span class="identifier">attribute_as</span></code> |
| utilizing SFINAE (i.e. <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">enable_if</span></code> |
| or <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">disable_if</span></code>). |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">void</span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <div class="variablelist"> |
| <p class="title"><b>Notation</b></p> |
| <dl> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">attr</span></code></span></dt> |
| <dd><p> |
| An instance of type <code class="computeroutput"><span class="identifier">Attrib</span></code>. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.advanced.customize.attribute_as.expression_semantics"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.expression_semantics-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.expression_semantics">Expression |
| Semantics</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attribute_as</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">>::</span><span class="identifier">type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The result type of the extraction. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attribute_as</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">>::</span><span class="identifier">call</span><span class="special">(</span><span class="identifier">attr</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Extract and return an instance of <code class="computeroutput"><span class="identifier">type</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attribute_as</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Attribute</span><span class="special">>::</span><span class="identifier">valid_as</span><span class="special">(</span><span class="identifier">attr</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Determine, at runtime, if the extraction of an instance of <code class="computeroutput"><span class="identifier">type</span></code> from <code class="computeroutput"><span class="identifier">attr</span></code> |
| would cause an error. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.advanced.customize.attribute_as.predefined_specializations"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.predefined_specializations-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.predefined_specializations">Predefined |
| Specializations</a> |
| </h6> |
| <p> |
| <a href="http://boost-spirit.com" target="_top">Spirit</a> predefines specializations |
| of this customization point for several types. The following table lists |
| those types together with the types exposed and the corresponding semantics: |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Template Parameters |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody><tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The exposed typedef <code class="computeroutput"><span class="identifier">type</span></code> |
| is defined to <code class="computeroutput"><span class="identifier">unused_type</span></code>. |
| The function <code class="computeroutput"><span class="identifier">call</span><span class="special">()</span></code> returns an instance of <code class="computeroutput"><span class="identifier">unused_type</span></code>. |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.advanced.customize.attribute_as.when_to_implement"></a><h6> |
| <a name="spirit.advanced.customize.attribute_as.when_to_implement-heading"></a> |
| <a class="link" href="attribute_as.html#spirit.advanced.customize.attribute_as.when_to_implement">When |
| to implement</a> |
| </h6> |
| <p> |
| This customization point may need to be implemented when using the <a class="link" href="../../karma/reference/directive/as.html" title="Generator Directives Forcing Atomic Extraction (as<T>, as_string[], as_wstring[])"><code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>[]</span></code></a> directive. |
| </p> |
| </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 © 2001-2011 Joel de Guzman, Hartmut Kaiser<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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