1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Generator Directives Forcing Atomic Extraction (as<T>, as_string[], as_wstring[])</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Spirit 2.5.8"> 8<link rel="up" href="../directive.html" title="Generator Directives"> 9<link rel="prev" href="columns.html" title="Generator Directive Separating Output Into Columns (columns[])"> 10<link rel="next" href="../nonterminal.html" title="Nonterminal Generators"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="columns.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../directive.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="../nonterminal.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<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 28 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> 29</h5></div></div></div> 30<h6> 31<a name="spirit.karma.reference.directive.as.h0"></a> 32 <span class="phrase"><a name="spirit.karma.reference.directive.as.description"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.description">Description</a> 33 </h6> 34<p> 35 The <code class="computeroutput"><span class="identifier">as</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> 36 class forces the atomic extraction of a container type <code class="computeroutput"><span class="identifier">T</span></code> from it's consumed attribute. Usually, 37 repetitive generators (such as <a class="link" href="../operator/kleene.html" title="Kleene Star Generator (*a)">Kleene 38 (<code class="computeroutput"><span class="special">*</span></code>)</a>, etc) or sequences 39 exposing a <code class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span></code> 40 will extract elements from the container supplied as their consumed attribute 41 by looping through the containers iterators. In some cases, this may 42 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 43 pass an unnamed temporary object of type <code class="computeroutput"><span class="identifier">T</span></code> 44 to it's subject, if extracting <code class="computeroutput"><span class="identifier">T</span></code> 45 from it's consumed attribute determined at generation-time to be valid. 46 <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> 47 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> 48 to determine validity; if it returns false, the generator fails. Subsequent 49 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>. 50 </p> 51<div class="note"><table border="0" summary="Note"> 52<tr> 53<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 54<th align="left">Note</th> 55</tr> 56<tr><td align="left" valign="top"><p> 57 <code class="computeroutput"><span class="identifier">T</span></code> is required to be 58 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 59 true for <code class="computeroutput"><span class="identifier">T</span></code>, a compile-time 60 error will occur. 61 </p></td></tr> 62</table></div> 63<h6> 64<a name="spirit.karma.reference.directive.as.h1"></a> 65 <span class="phrase"><a name="spirit.karma.reference.directive.as.header"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.header">Header</a> 66 </h6> 67<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/directive/as.hpp></span> 68<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> 69</pre> 70<p> 71 Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. 72 </p> 73<h6> 74<a name="spirit.karma.reference.directive.as.h2"></a> 75 <span class="phrase"><a name="spirit.karma.reference.directive.as.namespace"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.namespace">Namespace</a> 76 </h6> 77<div class="informaltable"><table class="table"> 78<colgroup><col></colgroup> 79<thead><tr><th> 80 <p> 81 Name 82 </p> 83 </th></tr></thead> 84<tbody> 85<tr><td> 86 <p> 87 <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">// 88 alias: boost::spirit::karma::as_string</span></code> 89 </p> 90 </td></tr> 91<tr><td> 92 <p> 93 <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">// 94 alias: boost::spirit::karma::as_wstring</span></code> 95 </p> 96 </td></tr> 97</tbody> 98</table></div> 99<h6> 100<a name="spirit.karma.reference.directive.as.h3"></a> 101 <span class="phrase"><a name="spirit.karma.reference.directive.as.synopsis"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.synopsis">Synopsis</a> 102 </h6> 103<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> 104<span class="keyword">struct</span> <span class="identifier">as</span><span class="special">;</span> 105</pre> 106<h6> 107<a name="spirit.karma.reference.directive.as.h4"></a> 108 <span class="phrase"><a name="spirit.karma.reference.directive.as.template_parameters"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.template_parameters">Template 109 parameters</a> 110 </h6> 111<div class="informaltable"><table class="table"> 112<colgroup> 113<col> 114<col> 115<col> 116</colgroup> 117<thead><tr> 118<th> 119 <p> 120 Parameter 121 </p> 122 </th> 123<th> 124 <p> 125 Description 126 </p> 127 </th> 128<th> 129 <p> 130 Default 131 </p> 132 </th> 133</tr></thead> 134<tbody><tr> 135<td> 136 <p> 137 <code class="computeroutput"><span class="identifier">T</span></code> 138 </p> 139 </td> 140<td> 141 <p> 142 A container type. 143 </p> 144 </td> 145<td> 146 <p> 147 none 148 </p> 149 </td> 150</tr></tbody> 151</table></div> 152<h6> 153<a name="spirit.karma.reference.directive.as.h5"></a> 154 <span class="phrase"><a name="spirit.karma.reference.directive.as.model_of"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.model_of">Model 155 of</a> 156 </h6> 157<div class="blockquote"><blockquote class="blockquote"><p> 158 <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a> 159 </p></blockquote></div> 160<div class="variablelist"> 161<p class="title"><b>Notation</b></p> 162<dl class="variablelist"> 163<dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt> 164<dd><p> 165 A <a class="link" href="../generator_concepts/generator.html" title="Generator"><code class="computeroutput"><span class="identifier">Generator</span></code></a>. 166 </p></dd> 167<dt><span class="term"><code class="computeroutput"><span class="identifier">attr</span></code></span></dt> 168<dd><p> 169 The attribute supplied to the directive. 170 </p></dd> 171</dl> 172</div> 173<h6> 174<a name="spirit.karma.reference.directive.as.h6"></a> 175 <span class="phrase"><a name="spirit.karma.reference.directive.as.expression_semantics"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.expression_semantics">Expression 176 Semantics</a> 177 </h6> 178<p> 179 Semantics of an expression is defined only where it differs from, or 180 is not defined in <a class="link" href="../generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</span></code></a>. 181 </p> 182<div class="informaltable"><table class="table"> 183<colgroup> 184<col> 185<col> 186</colgroup> 187<thead><tr> 188<th> 189 <p> 190 Expression 191 </p> 192 </th> 193<th> 194 <p> 195 Semantics 196 </p> 197 </th> 198</tr></thead> 199<tbody> 200<tr> 201<td> 202 <p> 203 <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> 204 </p> 205 </td> 206<td> 207 <p> 208 Extract an instance of <code class="computeroutput"><span class="identifier">T</span></code> 209 from <code class="computeroutput"><span class="identifier">attr</span></code>, 210 and invoke the subject generator <code class="computeroutput"><span class="identifier">a</span></code>, 211 supplying the unnamed temporary as it's attribute. 212 </p> 213 </td> 214</tr> 215<tr> 216<td> 217 <p> 218 <code class="computeroutput"><span class="identifier">as_string</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> 219 </p> 220 </td> 221<td> 222 <p> 223 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> 224 </p> 225 </td> 226</tr> 227<tr> 228<td> 229 <p> 230 <code class="computeroutput"><span class="identifier">as_wstring</span><span class="special">[</span><span class="identifier">a</span><span class="special">]</span></code> 231 </p> 232 </td> 233<td> 234 <p> 235 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> 236 </p> 237 </td> 238</tr> 239</tbody> 240</table></div> 241<h6> 242<a name="spirit.karma.reference.directive.as.h7"></a> 243 <span class="phrase"><a name="spirit.karma.reference.directive.as.attributes"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.attributes">Attributes</a> 244 </h6> 245<p> 246 See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.karma.quick_reference.compound_attribute_rules.notation">Compound 247 Attribute Notation</a>. 248 </p> 249<div class="informaltable"><table class="table"> 250<colgroup> 251<col> 252<col> 253</colgroup> 254<thead><tr> 255<th> 256 <p> 257 Expression 258 </p> 259 </th> 260<th> 261 <p> 262 Attribute 263 </p> 264 </th> 265</tr></thead> 266<tbody><tr> 267<td> 268 <p> 269 <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> 270 </p> 271 </td> 272<td> 273 <p> 274 <code class="computeroutput"><span class="identifier">a</span><span class="special">:</span> 275 <span class="identifier">A</span> <span class="special">--></span> 276 <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> 277 <span class="identifier">T</span></code> 278 </p> 279 </td> 280</tr></tbody> 281</table></div> 282<h6> 283<a name="spirit.karma.reference.directive.as.h8"></a> 284 <span class="phrase"><a name="spirit.karma.reference.directive.as.complexity"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.complexity">Complexity</a> 285 </h6> 286<div class="blockquote"><blockquote class="blockquote"><p> 287 The complexity is defined by the complexity of the subject generator, 288 <code class="computeroutput"><span class="identifier">a</span></code>, and the complexity 289 of the extraction unnamed contianer of type <code class="computeroutput"><span class="identifier">T</span></code> 290 from the attribute <code class="computeroutput"><span class="identifier">attr</span></code>. 291 </p></blockquote></div> 292<h6> 293<a name="spirit.karma.reference.directive.as.h9"></a> 294 <span class="phrase"><a name="spirit.karma.reference.directive.as.example"></a></span><a class="link" href="as.html#spirit.karma.reference.directive.as.example">Example</a> 295 </h6> 296<div class="note"><table border="0" summary="Note"> 297<tr> 298<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 299<th align="left">Note</th> 300</tr> 301<tr><td align="left" valign="top"><p> 302 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> 303 section. 304 </p></td></tr> 305</table></div> 306<p> 307 Some using declarations: 308 </p> 309<p> 310</p> 311<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> 312<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> 313<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> 314<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> 315<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> 316<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> 317<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> 318</pre> 319<p> 320 </p> 321<p> 322 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>, 323 <code class="computeroutput"><span class="identifier">as_string</span></code> and <code class="computeroutput"><span class="identifier">as_wstring</span></code>: 324 </p> 325<p> 326 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>. 327 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> 328 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. 329 </p> 330<p> 331</p> 332<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> 333<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> 334 335<span class="identifier">utree</span> <span class="identifier">ut</span><span class="special">;</span> 336<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> 337<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> 338 339<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> 340<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> 341 342<span class="identifier">ut</span><span class="special">.</span><span class="identifier">clear</span><span class="special">();</span> 343 344<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> 345<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> 346 347<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> 348<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> 349</pre> 350<p> 351 </p> 352</div> 353<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 354<td align="left"></td> 355<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 356 Distributed under the Boost Software License, Version 1.0. (See accompanying 357 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>) 358 </p> 359</div></td> 360</tr></table> 361<hr> 362<div class="spirit-nav"> 363<a accesskey="p" href="columns.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../directive.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="../nonterminal.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 364</div> 365</body> 366</html> 367
