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1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> 4<title>BOOST_PHOENIX_DEFINE_EXPRESSION</title> 5<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.76.1"> 7<link rel="home" href="../../../index.html" title="Chapter 1. Phoenix 3.0"> 8<link rel="up" href="../expression.html" title="Phoenix Expressions"> 9<link rel="prev" href="../expression.html" title="Phoenix Expressions"> 10<link rel="next" href="boost_phoenix_define_expression_vararg.html" title="BOOST_PHOENIX_DEFINE_EXPRESSION_VARARG"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../index.html">Home</a></td> 16<td align="center"><a 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name="phoenix.inside.expression.boost_phoenix_define_expression"></a><a class="link" href="boost_phoenix_define_expression.html" title="BOOST_PHOENIX_DEFINE_EXPRESSION">BOOST_PHOENIX_DEFINE_EXPRESSION</a> 28</h4></div></div></div> 29<a name="phoenix.inside.expression.boost_phoenix_define_expression.description"></a><h6> 30<a name="id623241"></a> 31 <a class="link" href="boost_phoenix_define_expression.html#phoenix.inside.expression.boost_phoenix_define_expression.description">Description</a> 32 </h6> 33<p> 34 <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_DEFINE_EXPRESSION</span></code> 35 is a macro that can be used to generate all the necessary boilerplate to 36 create Phoenix Expressions 37 </p> 38<a name="phoenix.inside.expression.boost_phoenix_define_expression.synopsis"></a><h6> 39<a name="id623276"></a> 40 <a class="link" href="boost_phoenix_define_expression.html#phoenix.inside.expression.boost_phoenix_define_expression.synopsis">Synopsis</a> 41 </h6> 42<pre class="programlisting"><span class="identifier">BOOST_PHOENIX_DEFINE_EXPRESSION</span><span class="special">(</span> 43 <span class="special">(</span><span class="identifier">namespace_seq</span><span class="special">)(</span><span class="identifier">name</span><span class="special">)</span> 44 <span class="special">,</span> <span class="special">(</span><span class="identifier">child_grammar0</span><span class="special">)</span> 45 <span class="special">(</span><span class="identifier">child_grammar1</span><span class="special">)</span> 46 <span class="special">...</span> 47<span class="special">)</span> 48</pre> 49<a name="phoenix.inside.expression.boost_phoenix_define_expression.semantics"></a><h6> 50<a name="id623381"></a> 51 <a class="link" href="boost_phoenix_define_expression.html#phoenix.inside.expression.boost_phoenix_define_expression.semantics">Semantics</a> 52 </h6> 53<p> 54 The above macro generates the necessary code for an expression <code class="computeroutput"><span class="identifier">name</span></code> in namespace <code class="computeroutput"><span class="identifier">namespace_seq</span></code>. 55 The sequence of <code class="computeroutput"><span class="special">(</span><span class="identifier">child_grammarN</span><span class="special">)</span></code> declares how many children the expression 56 will have and what <code class="computeroutput"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">grammar</span></code> 57 they match. 58 </p> 59<p> 60 The macro should be used at global scope. <code class="computeroutput"><span class="identifier">namespace_seq</span></code> 61 shall be the sequence of namespaces under which the following symbols will 62 be defined: 63 </p> 64<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">tag</span> 65<span class="special">{</span> 66 <span class="keyword">struct</span> <span class="identifier">name</span><span class="special">;</span> 67<span class="special">}</span> 68 69<span class="keyword">namespace</span> <span class="identifier">expression</span> 70<span class="special">{</span> 71 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">A0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A1</span> <span class="special">...</span> <span class="keyword">typename</span> <span class="identifier">AN</span><span class="special">></span> 72 <span class="keyword">struct</span> <span class="identifier">name</span> 73 <span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">expr</span><span class="special"><</span> 74 <span class="identifier">tag</span><span class="special">::</span><span class="identifier">name</span> 75 <span class="special">,</span> <span class="identifier">A0</span> 76 <span class="special">,</span> <span class="identifier">A1</span> 77 <span class="special">...</span> 78 <span class="special">,</span> <span class="identifier">AN</span> 79 <span class="special">></span> 80<span class="special">}</span> 81 82<span class="keyword">namespace</span> <span class="identifier">rule</span> 83<span class="special">{</span> 84 <span class="keyword">struct</span> <span class="identifier">name</span> 85 <span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">expr</span><span class="special"><</span> 86 <span class="identifier">child_grammar0</span> 87 <span class="special">,</span> <span class="identifier">child_grammar1</span> 88 <span class="special">...</span> 89 <span class="special">,</span> <span class="identifier">child_grammarN</span> 90 <span class="special">></span> 91 <span class="special">{};</span> 92<span class="special">}</span> 93</pre> 94<p> 95 This macros also adds a specialization for <code class="computeroutput"><span class="identifier">meta_grammar</span><span class="special">::</span><span class="identifier">case_</span><span class="special"><</span><span class="identifier">tag</span><span class="special">::</span><span class="identifier">name</span><span class="special">></span></code>. 96 </p> 97<a name="phoenix.inside.expression.boost_phoenix_define_expression.header"></a><h6> 98<a name="id623869"></a> 99 <a class="link" href="boost_phoenix_define_expression.html#phoenix.inside.expression.boost_phoenix_define_expression.header">Header</a> 100 </h6> 101<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="identifier">core</span><span class="special">/</span><span class="identifier">expression</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 102</pre> 103<a name="phoenix.inside.expression.boost_phoenix_define_expression.example"></a><h6> 104<a name="id623951"></a> 105 <a class="link" href="boost_phoenix_define_expression.html#phoenix.inside.expression.boost_phoenix_define_expression.example">Example</a> 106 </h6> 107<p> 108 The example from the previous section can be rewritten as: 109 </p> 110<pre class="programlisting"><span class="identifier">BOOST_PHOENIX_DEFINE_EXPRESSION</span><span class="special">(</span> 111 <span class="special">(</span><span class="identifier">plus</span><span class="special">)</span> 112 <span class="special">,</span> <span class="special">(</span><span class="identifier">meta_grammar</span><span class="special">)</span> <span class="comment">// Lhs 113</span> <span class="special">(</span><span class="identifier">meta_grammar</span><span class="special">)</span> <span class="comment">// Rhs 114</span><span class="special">)</span> 115 116<span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Lhs</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Rhs</span><span class="special">></span> 117<span class="keyword">typename</span> <span class="identifier">plus</span><span class="special"><</span><span class="identifier">Lhs</span><span class="special">,</span> <span class="identifier">Rhs</span><span class="special">>::</span><span class="identifier">type</span> 118<span class="identifier">plus</span><span class="special">(</span><span class="identifier">Lhs</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">lhs</span><span class="special">,</span> <span class="identifier">Rhs</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">rhs</span><span class="special">)</span> 119<span class="special">{</span> 120 <span class="keyword">return</span> <span class="identifier">expression</span><span class="special">::</span><span class="identifier">plus</span><span class="special"><</span><span class="identifier">Lhs</span><span class="special">,</span> <span class="identifier">Rhs</span><span class="special">>::</span><span class="identifier">make</span><span class="special">(</span><span class="identifier">lhs</span><span class="special">,</span> <span class="identifier">rhs</span><span class="special">);</span> 121<span class="special">}</span> 122</pre> 123</div> 124<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 125<td align="left"></td> 126<td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010 Joel de Guzman, Dan Marsden, Thomas Heller<p> 127 Distributed under the Boost Software License, Version 1.0. (See accompanying 128 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>) 129 </p> 130</div></td> 131</tr></table> 132<hr> 133<div class="spirit-nav"> 134<a accesskey="p" href="../expression.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../expression.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="boost_phoenix_define_expression_vararg.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 135</div> 136</body> 137</html>