libs/spirit/doc/html/spirit/karma/reference/auto.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Auto Generator</title>
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  20 </tr></table>
  21 <hr>
  22 <div class="spirit-nav">
  23 <a accesskey="p" href="action.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.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="auxiliary.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="spirit.karma.reference.auto"></a><a class="link" href="auto.html" title="Auto Generator">Auto Generator</a>
  28 </h4></div></div></div>
  29 <h6>
  30 <a name="spirit.karma.reference.auto.h0"></a>
  31           <span class="phrase"><a name="spirit.karma.reference.auto.description"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.description">Description</a>
  32         </h6>
  33 <p>
  34           This module includes the description of the <code class="computeroutput"><span class="identifier">auto_</span></code>
  35           generator. This generator can be used to automatically create a generator
  36           based on the supplied attribute type.
  37         </p>
  38 <h6>
  39 <a name="spirit.karma.reference.auto.h1"></a>
  40           <span class="phrase"><a name="spirit.karma.reference.auto.header"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.header">Header</a>
  41         </h6>
  42 <pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/karma/auto.hpp&gt;</span>
  43 <span class="preprocessor">#include</span> <span class="special">&lt;</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_auto</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  44 </pre>
  45 <p>
  46           Also, see <a class="link" href="../../structure/include.html" title="Include">Include Structure</a>.
  47         </p>
  48 <h6>
  49 <a name="spirit.karma.reference.auto.h2"></a>
  50           <span class="phrase"><a name="spirit.karma.reference.auto.namespace"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.namespace">Namespace</a>
  51         </h6>
  52 <div class="informaltable"><table class="table">
  53 <colgroup><col></colgroup>
  54 <thead><tr><th>
  55                   <p>
  56                     Name
  57                   </p>
  58                 </th></tr></thead>
  59 <tbody><tr><td>
  60                   <p>
  61                     <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">auto_</span> <span class="comment">// alias:
  62                     boost::spirit::karma::auto_</span></code>
  63                   </p>
  64                 </td></tr></tbody>
  65 </table></div>
  66 <h6>
  67 <a name="spirit.karma.reference.auto.h3"></a>
  68           <span class="phrase"><a name="spirit.karma.reference.auto.model_of"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.model_of">Model
  69           of</a>
  70         </h6>
  71 <div class="blockquote"><blockquote class="blockquote"><p>
  72             <a class="link" href="generator_concepts/primitivegenerator.html" title="PrimitiveGenerator"><code class="computeroutput"><span class="identifier">PrimitiveGenerator</span></code></a>
  73           </p></blockquote></div>
  74 <div class="variablelist">
  75 <p class="title"><b>Notation</b></p>
  76 <dl class="variablelist">
  77 <dt><span class="term"><code class="computeroutput"><span class="identifier">s</span></code></span></dt>
  78 <dd><p>
  79                 A variable instance of any type for which a mapping to a generator
  80                 type is defined (the meta function <code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">create_generator_exists</span></code>
  81                 returns <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>) or a <a class="link" href="basics.html#spirit.karma.reference.basics.lazy_argument">Lazy
  82                 Argument</a> that evaluates to any type for which a mapping to
  83                 a generator type is defined (the meta function <code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">create_generator_exists</span></code>
  84                 returns <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>).
  85               </p></dd>
  86 </dl>
  87 </div>
  88 <h6>
  89 <a name="spirit.karma.reference.auto.h4"></a>
  90           <span class="phrase"><a name="spirit.karma.reference.auto.expression_semantics"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.expression_semantics">Expression
  91           Semantics</a>
  92         </h6>
  93 <p>
  94           Semantics of an expression is defined only where it differs from, or is
  95           not defined in <a class="link" href="generator_concepts/primitivegenerator.html" title="PrimitiveGenerator"><code class="computeroutput"><span class="identifier">PrimitiveGenerator</span></code></a>.
  96         </p>
  97 <div class="informaltable"><table class="table">
  98 <colgroup>
  99 <col>
 100 <col>
 101 </colgroup>
 102 <thead><tr>
 103 <th>
 104                   <p>
 105                     Expression
 106                   </p>
 107                 </th>
 108 <th>
 109                   <p>
 110                     Description
 111                   </p>
 112                 </th>
 113 </tr></thead>
 114 <tbody>
 115 <tr>
 116 <td>
 117                   <p>
 118                     <code class="computeroutput"><span class="identifier">auto_</span></code>
 119                   </p>
 120                 </td>
 121 <td>
 122                   <p>
 123                     Create a generator instance compatible with the supplied attribute
 124                     type and use it for output generation. This generator never fails
 125                     (unless the underlying output stream reports an error).
 126                   </p>
 127                 </td>
 128 </tr>
 129 <tr>
 130 <td>
 131                   <p>
 132                     <code class="computeroutput"><span class="identifier">auto_</span><span class="special">(</span><span class="identifier">s</span><span class="special">)</span></code>
 133                   </p>
 134                 </td>
 135 <td>
 136                   <p>
 137                     Create a generator instance compatible with the supplied literal
 138                     value. This generator never fails (unless the underlying output
 139                     stream reports an error).
 140                   </p>
 141                 </td>
 142 </tr>
 143 </tbody>
 144 </table></div>
 145 <h6>
 146 <a name="spirit.karma.reference.auto.h5"></a>
 147           <span class="phrase"><a name="spirit.karma.reference.auto.additional_requirements"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.additional_requirements">Additional
 148           Requirements</a>
 149         </h6>
 150 <p>
 151           The <code class="computeroutput"><span class="identifier">auto_</span></code> generators can
 152           be used to emit output for any data type for which a mapping to a generator
 153           type is defined (the meta function <code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">create_generator_exists</span></code>
 154           returns <code class="computeroutput"><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span></code>). The following table outlines
 155           the predefined mapping rules from the attribute type to the generator type.
 156           These rules are applied recursively to create the generator type which
 157           can be used to generate output from the given attribute type.
 158         </p>
 159 <div class="informaltable"><table class="table">
 160 <colgroup>
 161 <col>
 162 <col>
 163 </colgroup>
 164 <thead><tr>
 165 <th>
 166                   <p>
 167                     Attribute type
 168                   </p>
 169                 </th>
 170 <th>
 171                   <p>
 172                     Generator type
 173                   </p>
 174                 </th>
 175 </tr></thead>
 176 <tbody>
 177 <tr>
 178 <td>
 179                   <p>
 180                     <code class="computeroutput"><span class="keyword">char</span></code>, <code class="computeroutput"><span class="keyword">wchar_t</span></code>
 181                   </p>
 182                 </td>
 183 <td>
 184                   <p>
 185                     <code class="computeroutput"><span class="identifier">standard</span><span class="special">::</span><span class="identifier">char_</span></code>, <code class="computeroutput"><span class="identifier">standard_wide</span><span class="special">::</span><span class="identifier">char_</span></code>
 186                   </p>
 187                 </td>
 188 </tr>
 189 <tr>
 190 <td>
 191                   <p>
 192                     <code class="computeroutput"><span class="keyword">short</span></code>, <code class="computeroutput"><span class="keyword">int</span></code>, <code class="computeroutput"><span class="keyword">long</span></code>
 193                   </p>
 194                 </td>
 195 <td>
 196                   <p>
 197                     <code class="computeroutput"><span class="identifier">short_</span></code>, <code class="computeroutput"><span class="identifier">int_</span></code>, <code class="computeroutput"><span class="identifier">long_</span></code>
 198                   </p>
 199                 </td>
 200 </tr>
 201 <tr>
 202 <td>
 203                   <p>
 204                     <code class="computeroutput"><span class="keyword">unsigned</span> <span class="keyword">short</span></code>,
 205                     <code class="computeroutput"><span class="keyword">unsigned</span> <span class="keyword">int</span></code>,
 206                     <code class="computeroutput"><span class="keyword">unsigned</span> <span class="keyword">long</span></code>
 207                   </p>
 208                 </td>
 209 <td>
 210                   <p>
 211                     <code class="computeroutput"><span class="identifier">ushort_</span></code>, <code class="computeroutput"><span class="identifier">uint_</span></code>, <code class="computeroutput"><span class="identifier">ulong_</span></code>
 212                   </p>
 213                 </td>
 214 </tr>
 215 <tr>
 216 <td>
 217                   <p>
 218                     <code class="computeroutput"><span class="keyword">float</span></code>, <code class="computeroutput"><span class="keyword">double</span></code>, <code class="computeroutput"><span class="keyword">long</span>
 219                     <span class="keyword">double</span></code>
 220                   </p>
 221                 </td>
 222 <td>
 223                   <p>
 224                     <code class="computeroutput"><span class="identifier">float_</span></code>, <code class="computeroutput"><span class="identifier">double_</span></code>, <code class="computeroutput"><span class="identifier">long_double</span></code>
 225                   </p>
 226                 </td>
 227 </tr>
 228 <tr>
 229 <td>
 230                   <p>
 231                     <code class="computeroutput"><span class="keyword">short</span></code>, <code class="computeroutput"><span class="keyword">int</span></code>, <code class="computeroutput"><span class="keyword">long</span></code>
 232                   </p>
 233                 </td>
 234 <td>
 235                   <p>
 236                     <code class="computeroutput"><span class="identifier">short_</span></code>, <code class="computeroutput"><span class="identifier">int_</span></code>, <code class="computeroutput"><span class="identifier">long_</span></code>
 237                   </p>
 238                 </td>
 239 </tr>
 240 <tr>
 241 <td>
 242                   <p>
 243                     <code class="computeroutput"><span class="keyword">long</span> <span class="keyword">long</span></code>,
 244                     <code class="computeroutput"><span class="keyword">unsigned</span> <span class="keyword">long</span>
 245                     <span class="keyword">long</span></code>
 246                   </p>
 247                 </td>
 248 <td>
 249                   <p>
 250                     <code class="computeroutput"><span class="identifier">long_long</span></code>, <code class="computeroutput"><span class="identifier">ulong_long</span></code>
 251                   </p>
 252                 </td>
 253 </tr>
 254 <tr>
 255 <td>
 256                   <p>
 257                     <code class="computeroutput"><span class="keyword">bool</span></code>
 258                   </p>
 259                 </td>
 260 <td>
 261                   <p>
 262                     <code class="computeroutput"><span class="identifier">bool_</span></code>
 263                   </p>
 264                 </td>
 265 </tr>
 266 <tr>
 267 <td>
 268                   <p>
 269                     Any string (<code class="computeroutput"><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*</span></code>,
 270                     <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>, etc.)
 271                   </p>
 272                 </td>
 273 <td>
 274                   <p>
 275                     <code class="computeroutput"><span class="identifier">string</span></code>
 276                   </p>
 277                 </td>
 278 </tr>
 279 <tr>
 280 <td>
 281                   <p>
 282                     Any (STL) container
 283                   </p>
 284                 </td>
 285 <td>
 286                   <p>
 287                     Kleene Star (unary <code class="computeroutput"><span class="char">'*'</span></code>)
 288                   </p>
 289                 </td>
 290 </tr>
 291 <tr>
 292 <td>
 293                   <p>
 294                     Any Fusion sequence
 295                   </p>
 296                 </td>
 297 <td>
 298                   <p>
 299                     Sequence operator (<code class="computeroutput"><span class="char">'&lt;&lt;'</span></code>)
 300                   </p>
 301                 </td>
 302 </tr>
 303 <tr>
 304 <td>
 305                   <p>
 306                     <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;&gt;</span></code>
 307                   </p>
 308                 </td>
 309 <td>
 310                   <p>
 311                     Optional operator (unary <code class="computeroutput"><span class="char">'-'</span></code>)
 312                   </p>
 313                 </td>
 314 </tr>
 315 <tr>
 316 <td>
 317                   <p>
 318                     <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special">&lt;&gt;</span></code>
 319                   </p>
 320                 </td>
 321 <td>
 322                   <p>
 323                     Alternative operator (<code class="computeroutput"><span class="char">'|'</span></code>)
 324                   </p>
 325                 </td>
 326 </tr>
 327 </tbody>
 328 </table></div>
 329 <p>
 330           It is possible to add support for any custom data type by implementing
 331           a specialization of the customization point <a class="link" href="../../advanced/customize/auto/create_generator.html" title="Define a Custom Attribute Mapping for a Generator"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">create_generator</span></code></a>. This customization
 332           can be used also to redefined any of the predefined mappings.
 333         </p>
 334 <h6>
 335 <a name="spirit.karma.reference.auto.h6"></a>
 336           <span class="phrase"><a name="spirit.karma.reference.auto.attributes"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.attributes">Attributes</a>
 337         </h6>
 338 <div class="informaltable"><table class="table">
 339 <colgroup>
 340 <col>
 341 <col>
 342 </colgroup>
 343 <thead><tr>
 344 <th>
 345                   <p>
 346                     Expression
 347                   </p>
 348                 </th>
 349 <th>
 350                   <p>
 351                     Attribute
 352                   </p>
 353                 </th>
 354 </tr></thead>
 355 <tbody>
 356 <tr>
 357 <td>
 358                   <p>
 359                     <code class="computeroutput"><span class="identifier">auto_</span></code>
 360                   </p>
 361                 </td>
 362 <td>
 363                   <p>
 364                     <code class="computeroutput"><span class="identifier">hold_any</span></code>, attribute
 365                     is mandatory (otherwise compilation will fail)
 366                   </p>
 367                 </td>
 368 </tr>
 369 <tr>
 370 <td>
 371                   <p>
 372                     <code class="computeroutput"><span class="identifier">auto_</span><span class="special">(</span><span class="identifier">s</span><span class="special">)</span></code>
 373                   </p>
 374                 </td>
 375 <td>
 376                   <p>
 377                     <code class="computeroutput"><span class="identifier">unused</span></code>
 378                   </p>
 379                 </td>
 380 </tr>
 381 </tbody>
 382 </table></div>
 383 <div class="important"><table border="0" summary="Important">
 384 <tr>
 385 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../images/important.png"></td>
 386 <th align="left">Important</th>
 387 </tr>
 388 <tr><td align="left" valign="top"><p>
 389             The attribute type <code class="computeroutput"><span class="identifier">hold_any</span></code>
 390             exposed by some of the <code class="computeroutput"><span class="identifier">auto_</span></code>
 391             generators is semantically and syntactically equivalent to the type implemented
 392             by <a href="../../../../../../../libs/any/index.html" target="_top">Boost.Any</a>. It has
 393             been added to <span class="emphasis"><em>Spirit</em></span> as it has better a performance
 394             and a smaller footprint if compared to <a href="../../../../../../../libs/any/index.html" target="_top">Boost.Any</a>.
 395           </p></td></tr>
 396 </table></div>
 397 <div class="note"><table border="0" summary="Note">
 398 <tr>
 399 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../images/note.png"></td>
 400 <th align="left">Note</th>
 401 </tr>
 402 <tr><td align="left" valign="top"><p>
 403             In addition to their usual attribute of type <code class="computeroutput"><span class="identifier">Attrib</span></code>
 404             all listed generators accept an instance of a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">Attrib</span><span class="special">&gt;</span></code> as well. If the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;&gt;</span></code> is initialized (holds a value)
 405             the generators behave as if their attribute was an instance of <code class="computeroutput"><span class="identifier">Attrib</span></code> and emit the value stored in
 406             the <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;&gt;</span></code>.
 407             Otherwise the generators will fail.
 408           </p></td></tr>
 409 </table></div>
 410 <h6>
 411 <a name="spirit.karma.reference.auto.h7"></a>
 412           <span class="phrase"><a name="spirit.karma.reference.auto.complexity"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.complexity">Complexity</a>
 413         </h6>
 414 <div class="blockquote"><blockquote class="blockquote"><p>
 415             The complexity of the <code class="computeroutput"><span class="identifier">auto_</span></code>
 416             generator depends on the attribute type. Each attribute type results
 417             in a different generator type to be instantiated which defines the overall
 418             complexity.
 419           </p></blockquote></div>
 420 <h6>
 421 <a name="spirit.karma.reference.auto.h8"></a>
 422           <span class="phrase"><a name="spirit.karma.reference.auto.example"></a></span><a class="link" href="auto.html#spirit.karma.reference.auto.example">Example</a>
 423         </h6>
 424 <div class="note"><table border="0" summary="Note">
 425 <tr>
 426 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../images/note.png"></td>
 427 <th align="left">Note</th>
 428 </tr>
 429 <tr><td align="left" valign="top"><p>
 430             The test harness for the example(s) below is presented in the <a class="link" href="basics.html#spirit.karma.reference.basics.examples">Basics
 431             Examples</a> section.
 432           </p></td></tr>
 433 </table></div>
 434 <p>
 435           Some includes:
 436         </p>
 437 <p>
 438 </p>
 439 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</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</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 440 <span class="preprocessor">#include</span> <span class="special">&lt;</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">support_utree</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 441 <span class="preprocessor">#include</span> <span class="special">&lt;</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">phoenix_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 442 <span class="preprocessor">#include</span> <span class="special">&lt;</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">phoenix_operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 443 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 444 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
 445 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">string</span><span class="special">&gt;</span>
 446 </pre>
 447 <p>
 448         </p>
 449 <p>
 450           Some using declarations:
 451         </p>
 452 <p>
 453 </p>
 454 <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">karma</span><span class="special">::</span><span class="identifier">auto_</span><span class="special">;</span>
 455 </pre>
 456 <p>
 457         </p>
 458 <p>
 459           And a class definition used in the examples:
 460         </p>
 461 <p>
 462 </p>
 463 <pre class="programlisting"><span class="comment">// a simple complex number representation z = a + bi</span>
 464 <span class="keyword">struct</span> <span class="identifier">complex</span>
 465 <span class="special">{</span>
 466     <span class="identifier">complex</span> <span class="special">(</span><span class="keyword">double</span> <span class="identifier">a</span><span class="special">,</span> <span class="keyword">double</span> <span class="identifier">b</span><span class="special">)</span>
 467       <span class="special">:</span> <span class="identifier">a</span><span class="special">(</span><span class="identifier">a</span><span class="special">),</span> <span class="identifier">b</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span>
 468     <span class="special">{}</span>
 469
 470     <span class="keyword">double</span> <span class="identifier">a</span><span class="special">;</span>
 471     <span class="keyword">double</span> <span class="identifier">b</span><span class="special">;</span>
 472 <span class="special">};</span>
 473 </pre>
 474 <p>
 475         </p>
 476 <p>
 477           The following construct is required to allow the <code class="computeroutput"><span class="identifier">complex</span></code>
 478           data structure to be utilized as a <a href="../../../../../../../libs/fusion/doc/html/index.html" target="_top">Boost.Fusion</a>
 479           sequence. This is required as we will emit output for this data structure
 480           with a <span class="emphasis"><em>Spirit.Karma</em></span> sequence: <code class="computeroutput"><span class="char">'{'</span>
 481           <span class="special">&lt;&lt;</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">','</span> <span class="special">&lt;&lt;</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">'}'</span></code>.
 482         </p>
 483 <p>
 484 </p>
 485 <pre class="programlisting"><span class="identifier">BOOST_FUSION_ADAPT_STRUCT</span><span class="special">(</span>
 486     <span class="identifier">complex</span><span class="special">,</span>
 487     <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">a</span><span class="special">)</span>
 488     <span class="special">(</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span>
 489 <span class="special">)</span>
 490 </pre>
 491 <p>
 492         </p>
 493 <p>
 494           We add a specialization for the create_generator customization point defining
 495           a custom output format for the complex type. Generally, any specialization
 496           for create_generator is expected to return the proto expression to be used
 497           to generate output for the type the customization point has been specialized
 498           for.
 499         </p>
 500 <p>
 501           We need to utilize <code class="computeroutput"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">deep_copy</span></code>
 502           as the expression contains literals (the <code class="computeroutput"><span class="char">'{'</span></code>,
 503           <code class="computeroutput"><span class="char">','</span></code>, and <code class="computeroutput"><span class="char">'}'</span></code>)
 504           which normally get embedded in the proto expression by reference only.
 505           The deep copy converts the proto tree to hold this by value. The deep copy
 506           operation can be left out for simpler proto expressions (not containing
 507           references to temporaries). Alternatively you could use the <code class="computeroutput"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">make_expr</span></code> facility to build the required
 508           proto expression.
 509         </p>
 510 <p>
 511 </p>
 512 <pre class="programlisting"><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>
 513 <span class="special">{</span>
 514     <span class="keyword">template</span> <span class="special">&lt;&gt;</span>
 515     <span class="keyword">struct</span> <span class="identifier">create_generator</span><span class="special">&lt;</span><span class="identifier">complex</span><span class="special">&gt;</span>
 516     <span class="special">{</span>
 517         <span class="keyword">typedef</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">deep_copy</span><span class="special">&lt;</span>
 518             <span class="identifier">BOOST_TYPEOF</span><span class="special">(</span><span class="char">'{'</span> <span class="special">&lt;&lt;</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">','</span> <span class="special">&lt;&lt;</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">'}'</span><span class="special">)</span>
 519         <span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">type</span><span class="special">;</span>
 520
 521         <span class="keyword">static</span> <span class="identifier">type</span> <span class="identifier">call</span><span class="special">()</span>
 522         <span class="special">{</span>
 523             <span class="keyword">return</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">deep_copy</span><span class="special">(</span>
 524                 <span class="char">'{'</span> <span class="special">&lt;&lt;</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">','</span> <span class="special">&lt;&lt;</span> <span class="identifier">karma</span><span class="special">::</span><span class="identifier">double_</span> <span class="special">&lt;&lt;</span> <span class="char">'}'</span><span class="special">);</span>
 525         <span class="special">}</span>
 526     <span class="special">};</span>
 527 <span class="special">}}}</span>
 528 </pre>
 529 <p>
 530         </p>
 531 <p>
 532           Some usage examples of <code class="computeroutput"><span class="identifier">auto_</span></code>
 533           generators:
 534         </p>
 535 <p>
 536           Emit a simple string using the <code class="computeroutput"><span class="identifier">karma</span><span class="special">::</span><span class="identifier">string</span></code>
 537           generator:
 538         </p>
 539 <p>
 540 </p>
 541 <pre class="programlisting"><span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"abc"</span><span class="special">,</span> <span class="identifier">auto_</span><span class="special">,</span> <span class="string">"abc"</span><span class="special">);</span>
 542 <span class="identifier">test_generator</span><span class="special">(</span><span class="string">"abc"</span><span class="special">,</span> <span class="identifier">auto_</span><span class="special">(</span><span class="string">"abc"</span><span class="special">));</span>
 543 </pre>
 544 <p>
 545         </p>
 546 <p>
 547           Emit instances of the <code class="computeroutput"><span class="identifier">complex</span></code>
 548           data type as defined above using the generator defined by the customization
 549           point for <code class="computeroutput"><span class="identifier">complex</span></code>:
 550         </p>
 551 <p>
 552 </p>
 553 <pre class="programlisting"><span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"{1.2,2.4}"</span><span class="special">,</span> <span class="identifier">auto_</span><span class="special">,</span> <span class="identifier">complex</span><span class="special">(</span><span class="number">1.2</span><span class="special">,</span> <span class="number">2.4</span><span class="special">));</span>
 554 <span class="identifier">test_generator</span><span class="special">(</span><span class="string">"{1.2,2.4}"</span><span class="special">,</span> <span class="identifier">auto_</span><span class="special">(</span><span class="identifier">complex</span><span class="special">(</span><span class="number">1.2</span><span class="special">,</span> <span class="number">2.4</span><span class="special">)));</span>
 555 </pre>
 556 <p>
 557         </p>
 558 </div>
 559 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 560 <td align="left"></td>
 561 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
 562         Distributed under the Boost Software License, Version 1.0. (See accompanying
 563         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>)
 564       </p>
 565 </div></td>
 566 </tr></table>
 567 <hr>
 568 <div class="spirit-nav">
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