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| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.auxiliary.attr_cast"></a><a class="link" href="attr_cast.html" title="Attribute Transformation Pseudo Generator (attr_cast)">Attribute |
| Transformation Pseudo Generator (<code class="computeroutput"><span class="identifier">attr_cast</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.description"></a><h6> |
| <a name="id863052"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.description">Description</a> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">,</span> |
| <span class="identifier">Transformed</span><span class="special">>()</span></code> |
| component invokes the embedded parser while supplying an attribute of |
| type <code class="computeroutput"><span class="identifier">Transformed</span></code>. The |
| supplied attribute gets created from the original attribute (of type |
| <code class="computeroutput"><span class="identifier">Exposed</span></code>) passed to this |
| component using the customization point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">transform_attribute</span></code></a>. |
| </p> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.header"></a><h6> |
| <a name="id863119"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/auxiliary/attr_cast.hpp> |
| </span><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">include</span><span class="special">/</span><span class="identifier">qi_attr_cast</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> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.namespace"></a><h6> |
| <a name="id863194"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.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">attr_cast</span> <span class="comment">// |
| alias: boost::spirit::qi::attr_cast</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.synopsis"></a><h6> |
| <a name="id863273"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.synopsis">Synopsis</a> |
| </h6> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="identifier">Exposed</span><span class="special">,</span> <span class="identifier">Transformed</span><span class="special">></span> |
| <span class="special"><</span><span class="identifier">unspecified</span><span class="special">></span> <span class="identifier">attr_cast</span><span class="special">(<</span><span class="identifier">unspecified</span><span class="special">>);</span> |
| </pre> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.template_parameters"></a><h6> |
| <a name="id863345"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.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">Exposed</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The type of the attribute supplied to the <code class="computeroutput"><span class="identifier">attr_cast</span></code>. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The type of the attribute expected by the embedded parser |
| <code class="computeroutput"><span class="identifier">p</span></code>. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| The <code class="computeroutput"><span class="identifier">attr_cast</span></code> is a function |
| template. It is possible to invoke it using the following schemes: |
| </p> |
| <pre class="programlisting"><span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span> |
| <span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span> |
| <span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">,</span> <span class="identifier">Transformed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span> |
| </pre> |
| <p> |
| depending on which of the attribute types can be deduced properly if |
| not explicitly specified. |
| </p> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.model_of"></a><h6> |
| <a name="id863584"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.model_of">Model |
| of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a> |
| </p></blockquote></div> |
| <div class="variablelist"> |
| <p class="title"><b>Notation</b></p> |
| <dl> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">p</span></code></span></dt> |
| <dd><p> |
| A parser object. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.expression_semantics"></a><h6> |
| <a name="id863642"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.expression_semantics">Expression |
| Semantics</a> |
| </h6> |
| <p> |
| Semantics of an expression is defined only where it differs from, or |
| is not defined in <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>. |
| </p> |
| <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">attr_cast</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a component invoking the parser <code class="computeroutput"><span class="identifier">p</span></code> |
| while passing an attribute of the type as normally expected |
| by <code class="computeroutput"><span class="identifier">p</span></code>. The type |
| of the supplied attribute will be transformed to the type |
| <code class="computeroutput"><span class="identifier">p</span></code> exposes as |
| its attribute type (by using the attribute customization point |
| <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">transform_attribute</span></code></a>). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a component invoking the parser <code class="computeroutput"><span class="identifier">p</span></code> |
| while passing an attribute of the type as normally expected |
| by <code class="computeroutput"><span class="identifier">p</span></code>. The supplied |
| attribute is expected to be of the type <code class="computeroutput"><span class="identifier">Exposed</span></code>, |
| it will be transformed to the type <code class="computeroutput"><span class="identifier">p</span></code> |
| exposes as its attribute type (using the attribute customization |
| point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">transform_attribute</span></code></a>). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">,</span> |
| <span class="identifier">Transformed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a component invoking the parser <code class="computeroutput"><span class="identifier">p</span></code> |
| while passing an attribute of type <code class="computeroutput"><span class="identifier">Transformed</span></code>. |
| The supplied attribute is expected to be of the type <code class="computeroutput"><span class="identifier">Exposed</span></code>, it will be transformed |
| to the type <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| (using the attribute customization point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">transform_attribute</span></code></a>). |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.attributes"></a><h6> |
| <a name="id863952"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.attributes">Attributes</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Attribute |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">p</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">p</span><span class="special">:</span> |
| <span class="identifier">A</span> <span class="special">--></span> |
| <span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">p</span><span class="special">):</span> |
| <span class="identifier">A</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">p</span><span class="special">:</span> |
| <span class="identifier">A</span> <span class="special">--></span> |
| <span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">):</span> |
| <span class="identifier">Exposed</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">,</span> |
| <span class="identifier">Transformed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">p</span><span class="special">:</span> |
| <span class="identifier">A</span> <span class="special">--></span> |
| <span class="identifier">attr_cast</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">,</span> |
| <span class="identifier">Transformed</span><span class="special">>(</span><span class="identifier">p</span><span class="special">):</span> |
| <span class="identifier">Exposed</span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.complexity"></a><h6> |
| <a name="id864276"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The complexity of this component is fully defined by the complexity |
| of the embedded parser <code class="computeroutput"><span class="identifier">p</span></code>. |
| </p></blockquote></div> |
| <a name="spirit.qi.reference.auxiliary.attr_cast.example"></a><h6> |
| <a name="id864304"></a> |
| <a class="link" href="attr_cast.html#spirit.qi.reference.auxiliary.attr_cast.example">Example</a> |
| </h6> |
| <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> |
| The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> |
| section. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Some using declarations: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">int_</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| The example references data structure <code class="computeroutput"><span class="identifier">int_data</span></code> |
| which needs a specialization of the customization point <a class="link" href="../../../advanced/customize/transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)"><code class="computeroutput"><span class="identifier">transform_attribute</span></code></a>: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="comment">// this is just a test structure we want to use in place of an int |
| </span><span class="keyword">struct</span> <span class="identifier">int_data</span> |
| <span class="special">{</span> |
| <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| |
| <span class="comment">// we provide a custom attribute transformation to allow its use as an int |
| </span><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">spirit</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">traits</span> |
| <span class="special">{</span> |
| <span class="comment">// in this case we just expose the embedded 'int' as the attribute instance |
| </span> <span class="comment">// to use, allowing to leave the function 'post()' empty |
| </span> <span class="keyword">template</span> <span class="special"><></span> |
| <span class="keyword">struct</span> <span class="identifier">transform_attribute</span><span class="special"><</span><span class="identifier">int_data</span><span class="special">,</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">domain</span><span class="special">></span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">type</span><span class="special">;</span> |
| <span class="keyword">static</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">pre</span><span class="special">(</span><span class="identifier">int_data</span><span class="special">&</span> <span class="identifier">d</span><span class="special">)</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">d</span><span class="special">.</span><span class="identifier">i</span><span class="special">;</span> <span class="special">}</span> |
| <span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">post</span><span class="special">(</span><span class="identifier">int_data</span><span class="special">&</span> <span class="identifier">val</span><span class="special">,</span> <span class="keyword">int</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">)</span> <span class="special">{}</span> |
| <span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">fail</span><span class="special">(</span><span class="identifier">int_data</span><span class="special">&)</span> <span class="special">{}</span> |
| <span class="special">};</span> |
| <span class="special">}}}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Now we use the <code class="computeroutput"><span class="identifier">attr_cast</span></code> |
| pseudo parser to invoke the attribute transformation: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">int_data</span> <span class="identifier">d</span> <span class="special">=</span> <span class="special">{</span> <span class="number">0</span> <span class="special">};</span> |
| <span class="identifier">test_parser_attr</span><span class="special">(</span><span class="string">"1"</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">qi</span><span class="special">::</span><span class="identifier">attr_cast</span><span class="special">(</span><span class="identifier">int_</span><span class="special">),</span> <span class="identifier">d</span><span class="special">);</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">d</span><span class="special">.</span><span class="identifier">i</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| </pre> |
| <p> |
| </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 © 2001-2010 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> |
| <hr> |
| <div class="spirit-nav"> |
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