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1 | <html> |
| 2 | <head> | |
| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>Actors in Detail</title> | |
| 5 | <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> | |
| 6 | <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> | |
| 7 | <link rel="home" href="../../index.html" title="Chapter 1. Phoenix 3.2.0"> | |
| 8 | <link rel="up" href="../inside.html" title="Inside Phoenix"> | |
| 9 | <link rel="prev" href="../inside.html" title="Inside Phoenix"> | |
| 10 | <link rel="next" href="expression.html" title="Phoenix Expressions"> | |
| 11 | </head> | |
| 12 | <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> | |
| 13 | <table cellpadding="2" width="100%"><tr> | |
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| 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="../inside.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../inside.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="expression.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h3 class="title"> | |
| 27 | <a name="phoenix.inside.actor"></a><a class="link" href="actor.html" title="Actors in Detail">Actors in Detail</a> | |
| 28 | </h3></div></div></div> | |
| 29 | <h5> | |
| 30 | <a name="phoenix.inside.actor.h0"></a> | |
| 31 | <span><a name="phoenix.inside.actor.actor"></a></span><a class="link" href="actor.html#phoenix.inside.actor.actor">Actor</a> | |
| 32 | </h5> | |
| 33 | <p> | |
| 34 | The main concept is the <code class="computeroutput"><span class="identifier">Actor</span></code>. | |
| 35 | An <code class="computeroutput"><span class="identifier">Actor</span></code> is a model of the | |
| 36 | <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/functional/concepts/poly.html" target="_top">Polymorphic | |
| 37 | Function Object</a> concept (that can accept 0 to N arguments (where | |
| 38 | N is a predefined maximum). | |
| 39 | </p> | |
| 40 | <p> | |
| 41 | An <code class="computeroutput"><span class="identifier">Actor</span></code> contains a valid | |
| 42 | Phoenix Expression, a call to one of the function call operator overloads, | |
| 43 | starts the evaluation process. | |
| 44 | </p> | |
| 45 | <div class="note"><table border="0" summary="Note"> | |
| 46 | <tr> | |
| 47 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
| 48 | <th align="left">Note</th> | |
| 49 | </tr> | |
| 50 | <tr><td align="left" valign="top"><p> | |
| 51 | You can set <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code>, | |
| 52 | the predefined maximum arity an actor can take. By default, <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code> is set to 10. | |
| 53 | </p></td></tr> | |
| 54 | </table></div> | |
| 55 | <p> | |
| 56 | The <code class="computeroutput"><span class="identifier">actor</span></code> template class | |
| 57 | models the <code class="computeroutput"><span class="identifier">Actor</span></code> concept: | |
| 58 | </p> | |
| 59 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">></span> | |
| 60 | <span class="keyword">struct</span> <span class="identifier">actor</span> | |
| 61 | <span class="special">{</span> | |
| 62 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">></span> | |
| 63 | <span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span> | |
| 64 | ||
| 65 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">>::</span><span class="identifier">type</span> | |
| 66 | <span class="keyword">operator</span><span class="special">()()</span> <span class="keyword">const</span><span class="special">;</span> | |
| 67 | ||
| 68 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">></span> | |
| 69 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">T0</span> <span class="special">&>::</span><span class="identifier">type</span> | |
| 70 | <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span><span class="special">&</span> <span class="identifier">_0</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> | |
| 71 | ||
| 72 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">></span> | |
| 73 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">T0</span> <span class="keyword">const</span> <span class="special">&>::</span><span class="identifier">type</span> | |
| 74 | <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">_0</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> | |
| 75 | ||
| 76 | <span class="comment">//...</span> | |
| 77 | <span class="special">};</span> | |
| 78 | </pre> | |
| 79 | <div class="table"> | |
| 80 | <a name="phoenix.inside.actor.t0"></a><p class="title"><b>Table 1.9. Actor Concept Requirements</b></p> | |
| 81 | <div class="table-contents"><table class="table" summary="Actor Concept Requirements"> | |
| 82 | <colgroup> | |
| 83 | <col> | |
| 84 | <col> | |
| 85 | </colgroup> | |
| 86 | <thead><tr> | |
| 87 | <th> | |
| 88 | <p> | |
| 89 | Expression | |
| 90 | </p> | |
| 91 | </th> | |
| 92 | <th> | |
| 93 | <p> | |
| 94 | Semantics | |
| 95 | </p> | |
| 96 | </th> | |
| 97 | </tr></thead> | |
| 98 | <tbody> | |
| 99 | <tr> | |
| 100 | <td> | |
| 101 | <p> | |
| 102 | <code class="computeroutput"><span class="identifier">actor</span><span class="special">(</span><span class="identifier">arg0</span><span class="special">,</span> | |
| 103 | <span class="identifier">arg1</span><span class="special">,</span> | |
| 104 | <span class="special">...,</span> <span class="identifier">argN</span><span class="special">)</span></code> | |
| 105 | </p> | |
| 106 | </td> | |
| 107 | <td> | |
| 108 | <p> | |
| 109 | Function call operators to start the evaluation | |
| 110 | </p> | |
| 111 | </td> | |
| 112 | </tr> | |
| 113 | <tr> | |
| 114 | <td> | |
| 115 | <p> | |
| 116 | <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span><span class="special"><</span><span class="identifier">Actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">>(</span><span class="identifier">Arg0</span><span class="special">,</span> | |
| 117 | <span class="identifier">Arg1</span><span class="special">,</span> | |
| 118 | <span class="special">...,</span> <span class="identifier">ArgN</span><span class="special">)>::</span><span class="identifier">type</span></code> | |
| 119 | </p> | |
| 120 | </td> | |
| 121 | <td> | |
| 122 | <p> | |
| 123 | Result of the evaluation | |
| 124 | </p> | |
| 125 | </td> | |
| 126 | </tr> | |
| 127 | <tr> | |
| 128 | <td> | |
| 129 | <p> | |
| 130 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> | |
| 131 | <span class="identifier">Arg0</span><span class="special">,</span> | |
| 132 | <span class="identifier">Arg1</span><span class="special">,</span> | |
| 133 | <span class="special">...,</span> <span class="identifier">ArgN</span><span class="special">>::</span><span class="identifier">type</span></code> | |
| 134 | </p> | |
| 135 | </td> | |
| 136 | <td> | |
| 137 | <p> | |
| 138 | Result of the evaluation | |
| 139 | </p> | |
| 140 | </td> | |
| 141 | </tr> | |
| 142 | </tbody> | |
| 143 | </table></div> | |
| 144 | </div> | |
| 145 | <br class="table-break"><h5> | |
| 146 | <a name="phoenix.inside.actor.h1"></a> | |
| 147 | <span><a name="phoenix.inside.actor.function_call_operators"></a></span><a class="link" href="actor.html#phoenix.inside.actor.function_call_operators">Function | |
| 148 | Call Operators</a> | |
| 149 | </h5> | |
| 150 | <p> | |
| 151 | There are 2*N function call operators for 0 to N arguments (N == <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code>). The actor class accepts | |
| 152 | the arguments and forwards the arguments to the default evaluation action. | |
| 153 | </p> | |
| 154 | <p> | |
| 155 | Additionally, there exist function call operators accepting permutations | |
| 156 | of const and non-const references. These operators are created for all N | |
| 157 | <= <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_PERFECT_FORWARD_LIMIT</span></code> | |
| 158 | (which defaults to 3). | |
| 159 | </p> | |
| 160 | <div class="note"><table border="0" summary="Note"> | |
| 161 | <tr> | |
| 162 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
| 163 | <th align="left">Note</th> | |
| 164 | </tr> | |
| 165 | <tr><td align="left" valign="top"> | |
| 166 | <p> | |
| 167 | <span class="bold"><strong>Forwarding Function Problem</strong></span> | |
| 168 | </p> | |
| 169 | <p> | |
| 170 | There is a known issue with current C++ called the "<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">Forwarding | |
| 171 | Function Problem</a>". The problem is that given an arbitrary | |
| 172 | function <code class="computeroutput"><span class="identifier">F</span></code>, using current | |
| 173 | C++ language rules, one cannot create a forwarding function <code class="computeroutput"><span class="identifier">FF</span></code> that transparently assumes the arguments | |
| 174 | of <code class="computeroutput"><span class="identifier">F</span></code>. | |
| 175 | </p> | |
| 176 | </td></tr> | |
| 177 | </table></div> | |
| 178 | <h5> | |
| 179 | <a name="phoenix.inside.actor.h2"></a> | |
| 180 | <span><a name="phoenix.inside.actor.context"></a></span><a class="link" href="actor.html#phoenix.inside.actor.context">Context</a> | |
| 181 | </h5> | |
| 182 | <p> | |
| 183 | On an actor function call, before calling the evaluation function, the actor | |
| 184 | created a <span class="bold"><strong>context</strong></span>. This context consists | |
| 185 | of an <code class="computeroutput"><span class="identifier">Environment</span></code> and an | |
| 186 | <code class="computeroutput"><span class="identifier">Action</span></code> part. These contain | |
| 187 | all information necessary to evaluate the given expression. | |
| 188 | </p> | |
| 189 | <div class="table"> | |
| 190 | <a name="phoenix.inside.actor.t1"></a><p class="title"><b>Table 1.10. Context Concept Requirements</b></p> | |
| 191 | <div class="table-contents"><table class="table" summary="Context Concept Requirements"> | |
| 192 | <colgroup> | |
| 193 | <col> | |
| 194 | <col> | |
| 195 | </colgroup> | |
| 196 | <thead><tr> | |
| 197 | <th> | |
| 198 | <p> | |
| 199 | Expression | |
| 200 | </p> | |
| 201 | </th> | |
| 202 | <th> | |
| 203 | <p> | |
| 204 | Semantics | |
| 205 | </p> | |
| 206 | </th> | |
| 207 | </tr></thead> | |
| 208 | <tbody> | |
| 209 | <tr> | |
| 210 | <td> | |
| 211 | <p> | |
| 212 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">context</span><span class="special"><</span><span class="identifier">Env</span><span class="special">,</span> | |
| 213 | <span class="identifier">Actions</span><span class="special">>::</span><span class="identifier">type</span></code> | |
| 214 | </p> | |
| 215 | </td> | |
| 216 | <td> | |
| 217 | <p> | |
| 218 | Type of a Context | |
| 219 | </p> | |
| 220 | </td> | |
| 221 | </tr> | |
| 222 | <tr> | |
| 223 | <td> | |
| 224 | <p> | |
| 225 | <code class="computeroutput"><span class="identifier">context</span><span class="special">(</span><span class="identifier">e</span><span class="special">,</span> | |
| 226 | <span class="identifier">a</span><span class="special">)</span></code> | |
| 227 | </p> | |
| 228 | </td> | |
| 229 | <td> | |
| 230 | <p> | |
| 231 | A Context containing environment <code class="computeroutput"><span class="identifier">e</span></code> | |
| 232 | and actions <code class="computeroutput"><span class="identifier">a</span></code> | |
| 233 | </p> | |
| 234 | </td> | |
| 235 | </tr> | |
| 236 | <tr> | |
| 237 | <td> | |
| 238 | <p> | |
| 239 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">env</span><span class="special"><</span><span class="identifier">Context</span><span class="special">>::</span><span class="identifier">type</span></code> | |
| 240 | </p> | |
| 241 | </td> | |
| 242 | <td> | |
| 243 | <p> | |
| 244 | Type of the contained Environment | |
| 245 | </p> | |
| 246 | </td> | |
| 247 | </tr> | |
| 248 | <tr> | |
| 249 | <td> | |
| 250 | <p> | |
| 251 | <code class="computeroutput"><span class="identifier">env</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code> | |
| 252 | </p> | |
| 253 | </td> | |
| 254 | <td> | |
| 255 | <p> | |
| 256 | The environment | |
| 257 | </p> | |
| 258 | </td> | |
| 259 | </tr> | |
| 260 | <tr> | |
| 261 | <td> | |
| 262 | <p> | |
| 263 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actions</span><span class="special"><</span><span class="identifier">Context</span><span class="special">>::</span><span class="identifier">type</span></code> | |
| 264 | </p> | |
| 265 | </td> | |
| 266 | <td> | |
| 267 | <p> | |
| 268 | Type of the contained Actions | |
| 269 | </p> | |
| 270 | </td> | |
| 271 | </tr> | |
| 272 | <tr> | |
| 273 | <td> | |
| 274 | <p> | |
| 275 | <code class="computeroutput"><span class="identifier">actions</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code> | |
| 276 | </p> | |
| 277 | </td> | |
| 278 | <td> | |
| 279 | <p> | |
| 280 | The actions | |
| 281 | </p> | |
| 282 | </td> | |
| 283 | </tr> | |
| 284 | </tbody> | |
| 285 | </table></div> | |
| 286 | </div> | |
| 287 | <br class="table-break"><h5> | |
| 288 | <a name="phoenix.inside.actor.h3"></a> | |
| 289 | <span><a name="phoenix.inside.actor.environment"></a></span><a class="link" href="actor.html#phoenix.inside.actor.environment">Environment</a> | |
| 290 | </h5> | |
| 291 | <p> | |
| 292 | The Environment is a model of <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/sequence/concepts/random_access_sequence.html" target="_top">Random | |
| 293 | Access Sequence</a>. | |
| 294 | </p> | |
| 295 | <p> | |
| 296 | The arguments passed to the actor's function call operator are collected | |
| 297 | inside the Environment: | |
| 298 | </p> | |
| 299 | <p> | |
| 300 | <span class="inlinemediaobject"><img src="../../images/funnel_in.png"></span> | |
| 301 | </p> | |
| 302 | <p> | |
| 303 | Other parts of the library (e.g. the scope module) extends the <code class="computeroutput"><span class="identifier">Environment</span></code> concept to hold other information | |
| 304 | such as local variables, etc. | |
| 305 | </p> | |
| 306 | <h5> | |
| 307 | <a name="phoenix.inside.actor.h4"></a> | |
| 308 | <span><a name="phoenix.inside.actor.actions"></a></span><a class="link" href="actor.html#phoenix.inside.actor.actions">Actions</a> | |
| 309 | </h5> | |
| 310 | <p> | |
| 311 | Actions is the part of Phoenix which are responsible for giving the actual | |
| 312 | expressions a specific behaviour. During the traversal of the Phoenix Expression | |
| 313 | Tree these actions are called whenever a specified rule in the grammar matches. | |
| 314 | </p> | |
| 315 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">actions</span> | |
| 316 | <span class="special">{</span> | |
| 317 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Rule</span><span class="special">></span> | |
| 318 | <span class="keyword">struct</span> <span class="identifier">when</span><span class="special">;</span> | |
| 319 | <span class="special">};</span> | |
| 320 | </pre> | |
| 321 | <p> | |
| 322 | The nested <code class="computeroutput"><span class="identifier">when</span></code> template | |
| 323 | is required to be <a href="http://www.boost.org/doc/libs/release/doc/html/PrimitiveTransform.html" target="_top">Proto | |
| 324 | Primitive Transform</a>. No worries, you don't have to learn <a href="http://www.boost.org/doc/libs/release/libs/proto/index.html" target="_top">Boost.Proto</a> | |
| 325 | just yet! Phoenix provides some wrappers to let you define simple actions | |
| 326 | without the need to dive deep into proto. | |
| 327 | </p> | |
| 328 | <p> | |
| 329 | Phoenix ships with a predefined <code class="computeroutput"><span class="identifier">default_actions</span></code> | |
| 330 | class that evaluates the expressions with C++ semantics: | |
| 331 | </p> | |
| 332 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">default_actions</span> | |
| 333 | <span class="special">{</span> | |
| 334 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Rule</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Dummy</span> <span class="special">=</span> <span class="keyword">void</span><span class="special">></span> | |
| 335 | <span class="keyword">struct</span> <span class="identifier">when</span> | |
| 336 | <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">_default</span><span class="special"><</span><span class="identifier">meta_grammar</span><span class="special">></span> | |
| 337 | <span class="special">{};</span> | |
| 338 | <span class="special">};</span> | |
| 339 | </pre> | |
| 340 | <p> | |
| 341 | For more information on how to use the default_actions class and how to attach | |
| 342 | custom actions to the evaluation process, see <a class="link" href="actions.html" title="More on Actions">more | |
| 343 | on actions</a>. | |
| 344 | </p> | |
| 345 | <h5> | |
| 346 | <a name="phoenix.inside.actor.h5"></a> | |
| 347 | <span><a name="phoenix.inside.actor.evaluation"></a></span><a class="link" href="actor.html#phoenix.inside.actor.evaluation">Evaluation</a> | |
| 348 | </h5> | |
| 349 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">evaluator</span> | |
| 350 | <span class="special">{</span> | |
| 351 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Context</span><span class="special">></span> | |
| 352 | <span class="emphasis"><em>unspecified</em></span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Expr</span> <span class="special">&,</span> <span class="identifier">Context</span> <span class="special">&);</span> | |
| 353 | <span class="special">};</span> | |
| 354 | ||
| 355 | <span class="identifier">evaluator</span> <span class="keyword">const</span> <span class="identifier">eval</span> <span class="special">=</span> <span class="special">{};</span> | |
| 356 | </pre> | |
| 357 | <p> | |
| 358 | The evaluation of a Phoenix expression is started by a call to the function | |
| 359 | call operator of <code class="computeroutput"><span class="identifier">evaluator</span></code>. | |
| 360 | </p> | |
| 361 | <p> | |
| 362 | The evaluator is called by the <code class="computeroutput"><span class="identifier">actor</span></code> | |
| 363 | function operator overloads after the context is built up. For reference, | |
| 364 | here is a typical <code class="computeroutput"><span class="identifier">actor</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> | |
| 365 | that accepts two arguments: | |
| 366 | </p> | |
| 367 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T1</span><span class="special">></span> | |
| 368 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">T0</span> <span class="special">&,</span> <span class="identifier">T1</span> <span class="special">&>::</span><span class="identifier">type</span> | |
| 369 | <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span> <span class="special">&</span><span class="identifier">t0</span><span class="special">,</span> <span class="identifier">T1</span> <span class="special">&</span><span class="identifier">t1</span><span class="special">)</span> <span class="keyword">const</span> | |
| 370 | <span class="special">{</span> | |
| 371 | <span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector2</span><span class="special"><</span><span class="identifier">T0</span> <span class="special">&,</span> <span class="identifier">T1</span> <span class="special">&></span> <span class="identifier">env</span><span class="special">(</span><span class="identifier">t0</span><span class="special">,</span> <span class="identifier">t1</span><span class="special">);</span> | |
| 372 | ||
| 373 | <span class="keyword">return</span> <span class="identifier">eval</span><span class="special">(*</span><span class="keyword">this</span><span class="special">,</span> <span class="identifier">context</span><span class="special">(</span><span class="identifier">env</span><span class="special">,</span> <span class="identifier">default_actions</span><span class="special">()));</span> | |
| 374 | <span class="special">}</span> | |
| 375 | </pre> | |
| 376 | <h5> | |
| 377 | <a name="phoenix.inside.actor.h6"></a> | |
| 378 | <span><a name="phoenix.inside.actor.result_of__actor"></a></span><a class="link" href="actor.html#phoenix.inside.actor.result_of__actor">result_of::actor</a> | |
| 379 | </h5> | |
| 380 | <p> | |
| 381 | For reasons of symmetry to the family of <code class="computeroutput"><span class="identifier">actor</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> there is a special metafunction usable | |
| 382 | for actor result type calculation named <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span></code>. | |
| 383 | This metafunction allows us to directly specify the types of the parameters | |
| 384 | to be passed to the <code class="computeroutput"><span class="identifier">actor</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> function. Here's a typical <code class="computeroutput"><span class="identifier">actor_result</span></code> that accepts two arguments: | |
| 385 | </p> | |
| 386 | <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">result_of</span> | |
| 387 | <span class="special">{</span> | |
| 388 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T1</span><span class="special">></span> | |
| 389 | <span class="keyword">struct</span> <span class="identifier">actor</span> | |
| 390 | <span class="special">{</span> | |
| 391 | <span class="keyword">typedef</span> <span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector2</span><span class="special"><</span><span class="identifier">T0</span><span class="special">,</span> <span class="identifier">T1</span><span class="special">></span> <span class="identifier">env_tpe</span><span class="special">;</span> | |
| 392 | <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">context</span><span class="special"><</span><span class="identifier">env_type</span><span class="special">,</span> <span class="identifier">default_actions</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">ctx_type</span> | |
| 393 | <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span><span class="special"><</span><span class="identifier">evaluator</span><span class="special">(</span><span class="identifier">Expr</span> <span class="keyword">const</span><span class="special">&,</span> <span class="identifier">ctx_type</span><span class="special">)>::</span><span class="identifier">type</span> <span class="identifier">type</span><span class="special">;</span> | |
| 394 | <span class="special">};</span> | |
| 395 | <span class="special">}</span> | |
| 396 | </pre> | |
| 397 | </div> | |
| 398 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 399 | <td align="left"></td> | |
| 400 | <td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas | |
| 401 | Heller, John Fletcher<p> | |
| 402 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 403 | 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>) | |
| 404 | </p> | |
| 405 | </div></td> | |
| 406 | </tr></table> | |
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