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| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit.advanced.customize.transform"></a><a class="link" href="transform.html" title="Transform an Attribute to a Different Type (Qi and Karma)">Transform an Attribute |
| to a Different Type (Qi and Karma)</a> |
| </h4></div></div></div> |
| <a name="spirit.advanced.customize.transform.transform_attribute"></a><h6> |
| <a name="id1162104"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.transform_attribute">transform_attribute</a> |
| </h6> |
| <p> |
| The template <code class="computeroutput"><span class="identifier">transform_attribute</span></code> |
| is a type used as an attribute customization point. It is invoked by <span class="emphasis"><em>Qi</em></span> |
| <code class="computeroutput"><span class="identifier">rule</span></code>, semantic action and |
| <code class="computeroutput"><span class="identifier">attr_cast</span></code>, and <span class="emphasis"><em>Karma</em></span> |
| <code class="computeroutput"><span class="identifier">rule</span></code>, semantic action and |
| <a class="link" href="../../karma/reference/auxiliary/attr_cast.html" title="Attribute Transformation Pseudo Generator (attr_cast)"><code class="computeroutput"><span class="identifier">attr_cast</span></code></a>. It is used to automatically |
| transform the user provided attribute to the attribute type expected by |
| the right hand side component (for <code class="computeroutput"><span class="identifier">rule</span></code>), |
| the semantic action, or the embedded component (for <code class="computeroutput"><span class="identifier">attr_cast</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="../../../images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| The interface of this customization point has been changed with Boost |
| V1.44. We added the <code class="computeroutput"><span class="identifier">Domain</span></code> |
| template parameter to allow for more fine grained specializations for |
| <span class="emphasis"><em>Spirit.Qi</em></span> and <span class="emphasis"><em>Spirit.Karma</em></span>. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.advanced.customize.transform.module_headers"></a><h6> |
| <a name="id1162202"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.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</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.transform.namespace"></a><h6> |
| <a name="id1162288"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.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.transform.synopsis"></a><h6> |
| <a name="id1162361"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.synopsis">Synopsis</a> |
| </h6> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Exposed</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Transformed</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Domain</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Enable</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">transform_attribute</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="special"><</span><span class="identifier">unspecified</span><span class="special">></span> <span class="identifier">type</span><span class="special">;</span> |
| <span class="keyword">static</span> <span class="identifier">type</span> <span class="identifier">pre</span><span class="special">(</span><span class="identifier">Exposed</span><span class="special">&</span> <span class="identifier">val</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">Exposed</span><span class="special">&</span> <span class="identifier">val</span><span class="special">,</span> <span class="identifier">type</span> <span class="identifier">attr</span><span class="special">);</span> <span class="comment">// Qi only |
| </span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="identifier">fail</span><span class="special">(</span><span class="identifier">Exposed</span><span class="special">&);</span> <span class="comment">// Qi only |
| </span><span class="special">};</span> |
| </pre> |
| <a name="spirit.advanced.customize.transform.template_parameters"></a><h6> |
| <a name="id1163280"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.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 attribute type supplied to the component which needs to be |
| transformed. |
| </p> |
| </td> |
| <td> |
| <p> |
| none |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The attribute type expected by the component to be provided as |
| the result of the transformation. |
| </p> |
| </td> |
| <td> |
| <p> |
| none |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Domain</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The domain of the sub library the template is instantiated in. |
| Typically this is either <code class="computeroutput"><span class="identifier">qi</span><span class="special">::</span><span class="identifier">domain</span></code> |
| or <code class="computeroutput"><span class="identifier">karma</span><span class="special">::</span><span class="identifier">domain</span></code>. |
| </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">transform_attribute</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> |
| <a name="spirit.advanced.customize.transform.notation"></a><h6> |
| <a name="id1163537"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.notation">Notation</a> |
| </h6> |
| <div class="variablelist"> |
| <p class="title"><b>Notation</b></p> |
| <dl> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Exposed</span></code></span></dt> |
| <dd><p> |
| The type, <code class="computeroutput"><span class="identifier">Exposed</span></code> |
| is the type of the attribute as passed in by the user. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Transformed</span></code></span></dt> |
| <dd><p> |
| The type, <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| is the type of the attribute as passed along to the right hand side |
| of the <code class="computeroutput"><span class="identifier">rule</span></code> (embedded |
| component of <code class="computeroutput"><span class="identifier">attr_cast</span></code>). |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Domain</span></code></span></dt> |
| <dd><p> |
| The domain of the sub library the template is instantiated in. Typically |
| this is either <code class="computeroutput"><span class="identifier">qi</span><span class="special">::</span><span class="identifier">domain</span></code> |
| or <code class="computeroutput"><span class="identifier">karma</span><span class="special">::</span><span class="identifier">domain</span></code>. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">exposed</span></code></span></dt> |
| <dd><p> |
| An instance of type <code class="computeroutput"><span class="identifier">Exposed</span></code>. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">transformed</span></code></span></dt> |
| <dd><p> |
| An instance of type <code class="computeroutput"><span class="identifier">Transformed</span></code>. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.advanced.customize.transform.expression_semantics"></a><h6> |
| <a name="id1163728"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.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">transform_attribute</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">Domain</span><span class="special">>::</span><span class="identifier">type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Evaluates to the type to be used as the result of the transformation |
| (to be passed to the right hand side of the <code class="computeroutput"><span class="identifier">rule</span></code> |
| or to the embedded component of the <code class="computeroutput"><span class="identifier">attr_cast</span></code>. |
| Most of the time this is equal to <code class="computeroutput"><span class="identifier">Transformed</span></code>, |
| but in other cases this might evaluate to <code class="computeroutput"><span class="identifier">Transformed</span><span class="special">&</span></code> instead avoiding superfluous |
| object creation. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| |
| </p> |
| <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">type</span> <span class="identifier">transform_attribute</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">Domain</span><span class="special">>::</span><span class="identifier">pre</span><span class="special">(</span><span class="identifier">exposed</span><span class="special">)</span></pre> |
| <p> |
| </p> |
| </td> |
| <td> |
| <p> |
| Do <code class="computeroutput"><span class="identifier">pre</span></code>-transformation |
| before invoking the right hand side component for <code class="computeroutput"><span class="identifier">rule</span></code> (or the embedded component |
| for <code class="computeroutput"><span class="identifier">attr_cast</span></code>). |
| This takes the attribute supplied as by the user (of type <code class="computeroutput"><span class="identifier">Exposed</span></code>) and returns the attribute |
| to be passed down the component hierarchy (of the type as exposed |
| by the metafunction <code class="computeroutput"><span class="identifier">type</span></code>). |
| This function will be called in <span class="emphasis"><em>Qi</em></span> and for |
| <span class="emphasis"><em>Karma</em></span>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| |
| </p> |
| <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">transform_attribute</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">Domain</span><span class="special">>::</span><span class="identifier">post</span><span class="special">(</span><span class="identifier">exposed</span><span class="special">,</span> <span class="identifier">transformed</span><span class="special">)</span></pre> |
| <p> |
| </p> |
| </td> |
| <td> |
| <p> |
| Do <code class="computeroutput"><span class="identifier">post</span></code>-transformation |
| after the invocation of the right hand side component for <code class="computeroutput"><span class="identifier">rule</span></code> (or the embedded component |
| for <code class="computeroutput"><span class="identifier">attr_cast</span></code>). |
| This takes the original attribute as supplied by the user and |
| the attribute as returned from the right hand side (embedded) |
| component and is expected to propagate the result back into the |
| supplied attribute instance. This function will be called in |
| <span class="emphasis"><em>Qi</em></span> only. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| |
| </p> |
| <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">transform_attribute</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">Domain</span><span class="special">>::</span><span class="identifier">fail</span><span class="special">(</span><span class="identifier">exposed</span><span class="special">)</span></pre> |
| <p> |
| </p> |
| </td> |
| <td> |
| <p> |
| Handling failing parse operations of the right hand side component |
| for <code class="computeroutput"><span class="identifier">rule</span></code> (or |
| the embedded component for <code class="computeroutput"><span class="identifier">attr_cast</span></code>). |
| This function will be called in <span class="emphasis"><em>Qi</em></span> only. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.advanced.customize.transform.predefined_specializations"></a><h6> |
| <a name="id1164183"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.predefined_specializations">Predefined |
| Specializations</a> |
| </h6> |
| <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">Exposed</span></code>, <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">type</span></code> evaluates |
| to <code class="computeroutput"><span class="identifier">Transformed</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| returns a new instance of <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| constructed from the argument of type <code class="computeroutput"><span class="identifier">Exposed</span></code>, |
| <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> |
| assigns <code class="computeroutput"><span class="identifier">transformed</span></code> |
| to <code class="computeroutput"><span class="identifier">exposed</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">></span></code>, |
| <code class="computeroutput"><span class="identifier">Transformed</span></code>, |
| <code class="computeroutput"><span class="keyword">typename</span> <span class="identifier">disable_if</span><span class="special"><</span><span class="identifier">is_same</span><span class="special"><</span><span class="identifier">optional</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">type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">type</span></code> evaluates |
| to <code class="computeroutput"><span class="identifier">Transformed</span><span class="special">&</span></code>, <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> returns a reference to the |
| instance of <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| stored in the passed optional (the argument of type <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">Exposed</span><span class="special">></span></code>), |
| the optional instance is initialized, if needed. <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> |
| does nothing, <code class="computeroutput"><span class="identifier">fail</span><span class="special">()</span></code> resets the optional (its parameter) |
| instance to the non-initialized state. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Exposed</span><span class="special">&</span></code>, |
| <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">type</span></code> evaluates |
| to <code class="computeroutput"><span class="identifier">Transformed</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| returns a new instance of <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| constructed from the argument of type <code class="computeroutput"><span class="identifier">Exposed</span></code>, |
| <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> |
| assigns <code class="computeroutput"><span class="identifier">transformed</span></code> |
| to <code class="computeroutput"><span class="identifier">exposed</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Attrib</span><span class="special">&</span></code>, |
| <code class="computeroutput"><span class="identifier">Attrib</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">type</span></code> evaluates |
| to <code class="computeroutput"><span class="identifier">Attrib</span><span class="special">&</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| returns it's argument, <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> does nothing. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Exposed</span> <span class="keyword">const</span></code>, |
| <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| (usind in <span class="emphasis"><em>Karma</em></span> only) <code class="computeroutput"><span class="identifier">type</span></code> |
| evaluates to <code class="computeroutput"><span class="identifier">Transformed</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| returns it's argument, <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> is not implemented. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Attrib</span> <span class="keyword">const</span><span class="special">&</span></code>, <code class="computeroutput"><span class="identifier">Attrib</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| (usind in <span class="emphasis"><em>Karma</em></span> only) <code class="computeroutput"><span class="identifier">type</span></code> |
| evaluates to <code class="computeroutput"><span class="identifier">Attrib</span> |
| <span class="keyword">const</span><span class="special">&</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| returns it's argument, <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> is not implemented. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Attrib</span> <span class="keyword">const</span></code>, |
| <code class="computeroutput"><span class="identifier">Attrib</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| (usind in <span class="emphasis"><em>Karma</em></span> only) <code class="computeroutput"><span class="identifier">type</span></code> |
| evaluates to <code class="computeroutput"><span class="identifier">Attrib</span> |
| <span class="keyword">const</span><span class="special">&</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| returns it's argument, <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> is not implemented. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">unused_type</span></code>, |
| <code class="computeroutput"><span class="identifier">Attrib</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">type</span></code> evaluates |
| to <code class="computeroutput"><span class="identifier">unused_type</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| and <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> |
| do nothing. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">Attrib</span></code>, <code class="computeroutput"><span class="identifier">unused_type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">type</span></code> evaluates |
| to <code class="computeroutput"><span class="identifier">unused_type</span></code>, |
| <code class="computeroutput"><span class="identifier">pre</span><span class="special">()</span></code> |
| and <code class="computeroutput"><span class="identifier">post</span><span class="special">()</span></code> |
| do nothing. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.advanced.customize.transform.when_to_implement"></a><h6> |
| <a name="id1165072"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.when_to_implement">When |
| to implement</a> |
| </h6> |
| <p> |
| The customization point <code class="computeroutput"><span class="identifier">transform_attribute</span></code> |
| needs to be implemented for a specific pair of types whenever the attribute |
| type supplied to a <code class="computeroutput"><span class="identifier">rule</span></code> |
| or <code class="computeroutput"><span class="identifier">attr_cast</span></code> cannot automatically |
| transformed to the attribute type expected by the right hand side of the |
| <code class="computeroutput"><span class="identifier">rule</span></code> (embedded component |
| of the <code class="computeroutput"><span class="identifier">attr_cast</span></code>) because |
| the default implementation as shown above is not applicable. Examples for |
| this could be that the type <code class="computeroutput"><span class="identifier">Transformed</span></code> |
| is not constructible from the type <code class="computeroutput"><span class="identifier">Exposed</span></code>. |
| </p> |
| <a name="spirit.advanced.customize.transform.example"></a><h6> |
| <a name="id1165139"></a> |
| <a class="link" href="transform.html#spirit.advanced.customize.transform.example">Example</a> |
| </h6> |
| <p> |
| TBD |
| </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> |
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