<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Attribute Transformation Pseudo Generator (attr_cast)</title> <link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.0"> <link rel="home" href="../../../../index.html" title="Spirit 2.4"> <link rel="up" href="../auxiliary.html" title="Auxiliary"> <link rel="prev" href="attr.html" title="Attribute (attr)"> <link rel="next" href="eol.html" title="End of Line (eol)"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="attr.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../auxiliary.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="eol.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> <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="id906287"></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="id906354"></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="id906428"></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="id906508"></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="id906580"></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="id906818"></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="id906877"></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="id907187"></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="id907511"></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="id907538"></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"> <a accesskey="p" href="attr.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../auxiliary.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="eol.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>