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  26 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  27 <a name="phoenix.actor"></a><a class="link" href="actor.html" title="Actor">Actor</a>
  28 </h2></div></div></div>
  29 <p>
  30       The <code class="computeroutput"><span class="identifier">Actor</span></code> is the main concept
  31       behind the library. Actors are function objects. An actor can accept 0 to
  32       <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code> arguments.
  33     </p>
  34 <div class="note"><table border="0" summary="Note">
  35 <tr>
  36 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
  37 <th align="left">Note</th>
  38 </tr>
  39 <tr><td align="left" valign="top"><p>
  40         You can set <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code>,
  41         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.
  42       </p></td></tr>
  43 </table></div>
  44 <p>
  45       Phoenix supplies an <code class="computeroutput"><span class="identifier">actor</span></code> class
  46       template whose specializations model the <code class="computeroutput"><span class="identifier">Actor</span></code>
  47       concept. <code class="computeroutput"><span class="identifier">actor</span></code> has one template
  48       parameter, <code class="computeroutput"><span class="identifier">Expr</span></code>, that supplies
  49       the underlying expression to evaluate.
  50     </p>
  51 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">&gt;</span>
  52 <span class="keyword">struct</span> <span class="identifier">actor</span>
  53 <span class="special">{</span>
  54     <span class="identifier">return_type</span>
  55     <span class="keyword">operator</span><span class="special">()()</span> <span class="keyword">const</span><span class="special">;</span>
  56
  57     <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">&gt;</span>
  58     <span class="identifier">return_type</span>
  59     <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span><span class="special">&amp;</span> <span class="identifier">_0</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  60
  61     <span class="keyword">template</span> <span class="special">&lt;</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">&gt;</span>
  62     <span class="identifier">return_type</span>
  63     <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span><span class="special">&amp;</span> <span class="identifier">_0</span><span class="special">,</span> <span class="identifier">T1</span><span class="special">&amp;</span> <span class="identifier">_1</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  64
  65     <span class="comment">//...</span>
  66 <span class="special">};</span>
  67 </pre>
  68 <p>
  69       The actor class accepts the arguments through a set of function call operators
  70       for 0 to <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code>
  71       arities (Don't worry about the details, for now. Note, for example, that we
  72       skimp over the details regarding <code class="computeroutput"><span class="identifier">return_type</span></code>).
  73       The arguments are passed through to the evaluation mechanism. For more information
  74       see <a class="link" href="inside/actor.html" title="Actors in Detail">Inside Actors</a>.
  75     </p>
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  79 <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2005, 2010, 2014 Joel de Guzman, Dan Marsden, Thomas Heller, John
  80       Fletcher<p>
  81         Distributed under the Boost Software License, Version 1.0. (See accompanying
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