| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Actors in Detail</title> |
| <link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> |
| <link rel="home" href="../../index.html" title="Chapter 1. Phoenix 3.2.0"> |
| <link rel="up" href="../inside.html" title="Inside Phoenix"> |
| <link rel="prev" href="../inside.html" title="Inside Phoenix"> |
| <link rel="next" href="expression.html" title="Phoenix Expressions"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> |
| <td align="center"><a href="../../../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <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> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="phoenix.inside.actor"></a><a class="link" href="actor.html" title="Actors in Detail">Actors in Detail</a> |
| </h3></div></div></div> |
| <h5> |
| <a name="phoenix.inside.actor.h0"></a> |
| <span class="phrase"><a name="phoenix.inside.actor.actor"></a></span><a class="link" href="actor.html#phoenix.inside.actor.actor">Actor</a> |
| </h5> |
| <p> |
| The main concept is the <code class="computeroutput"><span class="identifier">Actor</span></code>. |
| An <code class="computeroutput"><span class="identifier">Actor</span></code> is a model of the |
| <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/functional/concepts/poly.html" target="_top">Polymorphic |
| Function Object</a> concept (that can accept 0 to N arguments (where |
| N is a predefined maximum). |
| </p> |
| <p> |
| An <code class="computeroutput"><span class="identifier">Actor</span></code> contains a valid |
| Phoenix Expression, a call to one of the function call operator overloads, |
| starts the evaluation process. |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| You can set <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code>, |
| 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. |
| </p></td></tr> |
| </table></div> |
| <p> |
| The <code class="computeroutput"><span class="identifier">actor</span></code> template class |
| models the <code class="computeroutput"><span class="identifier">Actor</span></code> concept: |
| </p> |
| <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> |
| <span class="keyword">struct</span> <span class="identifier">actor</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span> |
| |
| <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> |
| <span class="keyword">operator</span><span class="special">()()</span> <span class="keyword">const</span><span class="special">;</span> |
| |
| <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">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> |
| <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> |
| |
| <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">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> |
| <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> |
| |
| <span class="comment">//...</span> |
| <span class="special">};</span> |
| </pre> |
| <div class="table"> |
| <a name="phoenix.inside.actor.t0"></a><p class="title"><b>Table 1.9. Actor Concept Requirements</b></p> |
| <div class="table-contents"><table class="table" summary="Actor Concept Requirements"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">actor</span><span class="special">(</span><span class="identifier">arg0</span><span class="special">,</span> |
| <span class="identifier">arg1</span><span class="special">,</span> |
| <span class="special">...,</span> <span class="identifier">argN</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Function call operators to start the evaluation |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <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> |
| <span class="identifier">Arg1</span><span class="special">,</span> |
| <span class="special">...,</span> <span class="identifier">ArgN</span><span class="special">)>::</span><span class="identifier">type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Result of the evaluation |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <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> |
| <span class="identifier">Arg0</span><span class="special">,</span> |
| <span class="identifier">Arg1</span><span class="special">,</span> |
| <span class="special">...,</span> <span class="identifier">ArgN</span><span class="special">>::</span><span class="identifier">type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Result of the evaluation |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| </div> |
| <br class="table-break"><h5> |
| <a name="phoenix.inside.actor.h1"></a> |
| <span class="phrase"><a name="phoenix.inside.actor.function_call_operators"></a></span><a class="link" href="actor.html#phoenix.inside.actor.function_call_operators">Function |
| Call Operators</a> |
| </h5> |
| <p> |
| 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 |
| the arguments and forwards the arguments to the default evaluation action. |
| </p> |
| <p> |
| Additionally, there exist function call operators accepting permutations |
| of const and non-const references. These operators are created for all N |
| <= <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_PERFECT_FORWARD_LIMIT</span></code> |
| (which defaults to 3). |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"> |
| <p> |
| <span class="bold"><strong>Forwarding Function Problem</strong></span> |
| </p> |
| <p> |
| 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 |
| Function Problem</a>". The problem is that given an arbitrary |
| function <code class="computeroutput"><span class="identifier">F</span></code>, using current |
| C++ language rules, one cannot create a forwarding function <code class="computeroutput"><span class="identifier">FF</span></code> that transparently assumes the arguments |
| of <code class="computeroutput"><span class="identifier">F</span></code>. |
| </p> |
| </td></tr> |
| </table></div> |
| <h5> |
| <a name="phoenix.inside.actor.h2"></a> |
| <span class="phrase"><a name="phoenix.inside.actor.context"></a></span><a class="link" href="actor.html#phoenix.inside.actor.context">Context</a> |
| </h5> |
| <p> |
| On an actor function call, before calling the evaluation function, the actor |
| created a <span class="bold"><strong>context</strong></span>. This context consists |
| of an <code class="computeroutput"><span class="identifier">Environment</span></code> and an |
| <code class="computeroutput"><span class="identifier">Action</span></code> part. These contain |
| all information necessary to evaluate the given expression. |
| </p> |
| <div class="table"> |
| <a name="phoenix.inside.actor.t1"></a><p class="title"><b>Table 1.10. Context Concept Requirements</b></p> |
| <div class="table-contents"><table class="table" summary="Context Concept Requirements"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Expression |
| </p> |
| </th> |
| <th> |
| <p> |
| Semantics |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">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> |
| <span class="identifier">Actions</span><span class="special">>::</span><span class="identifier">type</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Type of a Context |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">context</span><span class="special">(</span><span class="identifier">e</span><span class="special">,</span> |
| <span class="identifier">a</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| A Context containing environment <code class="computeroutput"><span class="identifier">e</span></code> |
| and actions <code class="computeroutput"><span class="identifier">a</span></code> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| <td> |
| <p> |
| Type of the contained Environment |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">env</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The environment |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <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> |
| </p> |
| </td> |
| <td> |
| <p> |
| Type of the contained Actions |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">actions</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The actions |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| </div> |
| <br class="table-break"><h5> |
| <a name="phoenix.inside.actor.h3"></a> |
| <span class="phrase"><a name="phoenix.inside.actor.environment"></a></span><a class="link" href="actor.html#phoenix.inside.actor.environment">Environment</a> |
| </h5> |
| <p> |
| 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 |
| Access Sequence</a>. |
| </p> |
| <p> |
| The arguments passed to the actor's function call operator are collected |
| inside the Environment: |
| </p> |
| <p> |
| <span class="inlinemediaobject"><img src="../../images/funnel_in.png"></span> |
| </p> |
| <p> |
| 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 |
| such as local variables, etc. |
| </p> |
| <h5> |
| <a name="phoenix.inside.actor.h4"></a> |
| <span class="phrase"><a name="phoenix.inside.actor.actions"></a></span><a class="link" href="actor.html#phoenix.inside.actor.actions">Actions</a> |
| </h5> |
| <p> |
| Actions is the part of Phoenix which are responsible for giving the actual |
| expressions a specific behaviour. During the traversal of the Phoenix Expression |
| Tree these actions are called whenever a specified rule in the grammar matches. |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">actions</span> |
| <span class="special">{</span> |
| <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">struct</span> <span class="identifier">when</span><span class="special">;</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| The nested <code class="computeroutput"><span class="identifier">when</span></code> template |
| is required to be <a href="http://www.boost.org/doc/libs/release/doc/html/PrimitiveTransform.html" target="_top">Proto |
| 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> |
| just yet! Phoenix provides some wrappers to let you define simple actions |
| without the need to dive deep into proto. |
| </p> |
| <p> |
| Phoenix ships with a predefined <code class="computeroutput"><span class="identifier">default_actions</span></code> |
| class that evaluates the expressions with C++ semantics: |
| </p> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">default_actions</span> |
| <span class="special">{</span> |
| <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> |
| <span class="keyword">struct</span> <span class="identifier">when</span> |
| <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> |
| <span class="special">{};</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| For more information on how to use the default_actions class and how to attach |
| custom actions to the evaluation process, see <a class="link" href="actions.html" title="More on Actions">more |
| on actions</a>. |
| </p> |
| <h5> |
| <a name="phoenix.inside.actor.h5"></a> |
| <span class="phrase"><a name="phoenix.inside.actor.evaluation"></a></span><a class="link" href="actor.html#phoenix.inside.actor.evaluation">Evaluation</a> |
| </h5> |
| <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">evaluator</span> |
| <span class="special">{</span> |
| <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> |
| <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> |
| <span class="special">};</span> |
| |
| <span class="identifier">evaluator</span> <span class="keyword">const</span> <span class="identifier">eval</span> <span class="special">=</span> <span class="special">{};</span> |
| </pre> |
| <p> |
| The evaluation of a Phoenix expression is started by a call to the function |
| call operator of <code class="computeroutput"><span class="identifier">evaluator</span></code>. |
| </p> |
| <p> |
| The evaluator is called by the <code class="computeroutput"><span class="identifier">actor</span></code> |
| function operator overloads after the context is built up. For reference, |
| 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> |
| that accepts two arguments: |
| </p> |
| <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> |
| <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> |
| <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> |
| <span class="special">{</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</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="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> |
| <span class="special">}</span> |
| </pre> |
| <h5> |
| <a name="phoenix.inside.actor.h6"></a> |
| <span class="phrase"><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> |
| </h5> |
| <p> |
| 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 |
| 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>. |
| This metafunction allows us to directly specify the types of the parameters |
| 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: |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">result_of</span> |
| <span class="special">{</span> |
| <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> |
| <span class="keyword">struct</span> <span class="identifier">actor</span> |
| <span class="special">{</span> |
| <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> |
| <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> |
| <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> |
| <span class="special">};</span> |
| <span class="special">}</span> |
| </pre> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas |
| Heller, John Fletcher<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <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> |
| </div> |
| </body> |
| </html> |
