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| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.karma.reference.directive.as"></a><a class="link" href="as.html" title="Generator Directives Forcing Atomic Extraction (as<T>, as_string[], as_wstring[])">Generator Directives |
| Forcing Atomic Extraction (<code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>,</span> <span class="identifier">as_string</span><span class="special">[],</span> <span class="identifier">as_wstring</span><span class="special">[]</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.karma.reference.directive.as.description"></a><h6> |
| <a name="spirit.karma.reference.directive.as.description-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.as.description">Description</a> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> |
| class forces the atomic extraction of a container type <code class="computeroutput"><span class="identifier">T</span></code> from it's consumed attribute. Usually, |
| repetitive generators (such as <a class="link" href="../operator/kleene.html" title="Kleene Star Generator (*a)">Kleene |
| (<code class="computeroutput"><span class="special">*</span></code>)</a>, etc) or sequences |
| exposing a <code class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> |
| will extract elements from the container supplied as their consumed attribute |
| by looping through the containers iterators. In some cases, this may |
| be undesirable. The <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> class creates a directive that will |
| pass an unnamed temporary object of type <code class="computeroutput"><span class="identifier">T</span></code> |
| to it's subject, if extracting <code class="computeroutput"><span class="identifier">T</span></code> |
| from it's consumed attribute determined at generation-time to be valid. |
| <a class="link" href="../../../advanced/customize/attribute_as.html" title="Atomically Extract an Attribute Value from a Container (Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">valid_as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span></code></a> |
| is called by <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> |
| to determine validity; if it returns false, the generator fails. Subsequent |
| extraction is performed by calling <a class="link" href="../../../advanced/customize/attribute_as.html" title="Atomically Extract an Attribute Value from a Container (Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span></code></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> |
| <code class="computeroutput"><span class="identifier">T</span></code> is required to be |
| a container type. If <a class="link" href="../../../advanced/customize/is_container.html" title="Determine if a Type Should be Treated as a Container (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_container</span></code></a> does not return |
| true for <code class="computeroutput"><span class="identifier">T</span></code>, a compile-time |
| error will occur. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.karma.reference.directive.as.header"></a><h6> |
| <a name="spirit.karma.reference.directive.as.header-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.as.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/directive/as.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">karma_as</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.karma.reference.directive.as.namespace"></a><h6> |
| <a name="spirit.karma.reference.directive.as.namespace-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.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">as_string</span> <span class="comment">// |
| alias: boost::spirit::karma::as_string</span></code> |
| </p> |
| </td></tr> |
| <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">as_wstring</span> <span class="comment">// |
| alias: boost::spirit::karma::as_wstring</span></code> |
| </p> |
| </td></tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.karma.reference.directive.as.synopsis"></a><h6> |
| <a name="spirit.karma.reference.directive.as.synopsis-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.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">struct</span> <span class="identifier">as</span><span class="special">;</span> |
| </pre> |
| <a name="spirit.karma.reference.directive.as.template_parameters"></a><h6> |
| <a name="spirit.karma.reference.directive.as.template_parameters-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.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> |
| A container type. |
| </p> |
| </td> |
| <td> |
| <p> |
| none |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.karma.reference.directive.as.model_of"></a><h6> |
| <a name="spirit.karma.reference.directive.as.model_of-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.as.model_of">Model of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</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">a</span></code></span></dt> |
| <dd><p> |
| A <a class="link" href="../generator_concepts/generator.html" title="Generator"><code class="computeroutput"><span class="identifier">Generator</span></code></a>. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">attr</span></code></span></dt> |
| <dd><p> |
| The attribute supplied to the directive. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.karma.reference.directive.as.expression_semantics"></a><h6> |
| <a name="spirit.karma.reference.directive.as.expression_semantics-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.as.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="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</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">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Extract an instance of <code class="computeroutput"><span class="identifier">T</span></code> |
| from <code class="computeroutput"><span class="identifier">attr</span></code>, |
| and invoke the subject generator <code class="computeroutput"><span class="identifier">a</span></code>, |
| supplying the unnamed temporary as it's attribute. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">as_string</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Equivalent to <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>()[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">as_wstring</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Equivalent to <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">wstring</span><span class="special">>()[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.karma.reference.directive.as.attributes"></a><h6> |
| <a name="spirit.karma.reference.directive.as.attributes-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.as.attributes">Attributes</a> |
| </h6> |
| <p> |
| See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound |
| Attribute Notation</a>. |
| </p> |
| <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">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()[</span><span class="identifier">a</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">a</span><span class="special">:</span> |
| <span class="identifier">A</span> <span class="special">--></span> |
| <span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()[</span><span class="identifier">a</span><span class="special">]:</span> |
| <span class="identifier">T</span></code> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.karma.reference.directive.as.complexity"></a><h6> |
| <a name="spirit.karma.reference.directive.as.complexity-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.as.complexity">Complexity</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| The complexity is defined by the complexity of the subject generator, |
| <code class="computeroutput"><span class="identifier">a</span></code>, and the complexity |
| of the extraction unnamed contianer of type <code class="computeroutput"><span class="identifier">T</span></code> |
| from the attribute <code class="computeroutput"><span class="identifier">attr</span></code>. |
| </p></blockquote></div> |
| <a name="spirit.karma.reference.directive.as.example"></a><h6> |
| <a name="spirit.karma.reference.directive.as.example-heading"></a> |
| <a class="link" href="as.html#spirit.karma.reference.directive.as.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.karma.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">utree</span><span class="special">;</span> |
| <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">utree_type</span><span class="special">;</span> |
| <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">utf8_symbol_type</span><span class="special">;</span> |
| <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">karma</span><span class="special">::</span><span class="identifier">as</span><span class="special">;</span> |
| <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">karma</span><span class="special">::</span><span class="identifier">as_string</span><span class="special">;</span> |
| <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">karma</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> |
| <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">karma</span><span class="special">::</span><span class="identifier">double_</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Simple usage of <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>, |
| <code class="computeroutput"><span class="identifier">as_string</span></code> and <code class="computeroutput"><span class="identifier">as_wstring</span></code>: |
| </p> |
| <p> |
| To properly handle string concatenation with <a class="link" href="../../../support/utree.html" title="The utree data structure"><code class="computeroutput"><span class="identifier">utree</span></code></a>, we make use of <code class="computeroutput"><span class="identifier">as_string</span><span class="special">[]</span></code>. |
| We also use <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> |
| to explicitly extract a <a class="link" href="../../../support/utree.html" title="The utree data structure"><code class="computeroutput"><span class="identifier">utree</span></code></a> symbol node. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">as</span><span class="special"><</span><span class="identifier">utf8_symbol_type</span><span class="special">></span> <span class="identifier">as_symbol_type</span><span class="special">;</span> |
| <span class="identifier">as_symbol_type</span> <span class="keyword">const</span> <span class="identifier">as_symbol</span> <span class="special">=</span> <span class="identifier">as_symbol_type</span><span class="special">();</span> |
| |
| <span class="identifier">utree</span> <span class="identifier">ut</span><span class="special">;</span> |
| <span class="identifier">ut</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="string">"xyz"</span><span class="special">);</span> |
| <span class="identifier">ut</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">1.23</span><span class="special">);</span> |
| |
| <span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"xyz1.23"</span><span class="special">,</span> <span class="identifier">as_string</span><span class="special">[*</span><span class="identifier">char_</span><span class="special">]</span> <span class="special"><<</span> <span class="identifier">double_</span><span class="special">,</span> <span class="identifier">ut</span><span class="special">);</span> |
| <span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"xyz1.23"</span><span class="special">,</span> <span class="identifier">as</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>()[*</span><span class="identifier">char_</span><span class="special">]</span> <span class="special"><<</span> <span class="identifier">double_</span><span class="special">,</span> <span class="identifier">ut</span><span class="special">);</span> |
| |
| <span class="identifier">ut</span><span class="special">.</span><span class="identifier">clear</span><span class="special">();</span> |
| |
| <span class="identifier">ut</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">utf8_symbol_type</span><span class="special">(</span><span class="string">"xyz"</span><span class="special">));</span> |
| <span class="identifier">ut</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="number">1.23</span><span class="special">);</span> |
| |
| <span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"xyz1.23"</span><span class="special">,</span> <span class="identifier">as_symbol</span><span class="special">[*</span><span class="identifier">char_</span><span class="special">]</span> <span class="special"><<</span> <span class="identifier">double_</span><span class="special">,</span> <span class="identifier">ut</span><span class="special">);</span> |
| <span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"xyz1.23"</span><span class="special">,</span> <span class="identifier">as</span><span class="special"><</span><span class="identifier">utf8_symbol_type</span><span class="special">>()[*</span><span class="identifier">char_</span><span class="special">]</span> <span class="special"><<</span> <span class="identifier">double_</span><span class="special">,</span> <span class="identifier">ut</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 © 2001-2011 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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