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1 | <html> |
| 2 | <head> | |
| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>Custom Terminals</title> | |
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| 7 | <link rel="home" href="../../index.html" title="Chapter 1. Phoenix 3.2.0"> | |
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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h3 class="title"> | |
| 27 | <a name="phoenix.inside.custom_terminals"></a><a class="link" href="custom_terminals.html" title="Custom Terminals">Custom Terminals</a> | |
| 28 | </h3></div></div></div> | |
| 29 | <p> | |
| 30 | Custom Terminals are used in Phoenix to handle special values transparently. | |
| 31 | For example, as Phoenix captures everything by value, we needed to use <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span></code> to bring reference semantics | |
| 32 | into Phoenix. | |
| 33 | </p> | |
| 34 | <p> | |
| 35 | Custom terminals could be any wrapper class: | |
| 36 | </p> | |
| 37 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> | |
| 38 | <span class="keyword">struct</span> <span class="identifier">is_custom_terminal</span><span class="special">;</span> | |
| 39 | </pre> | |
| 40 | <p> | |
| 41 | needs to be specialized in order for Phoenix to recognize this wrapper type. | |
| 42 | <code class="computeroutput"><span class="identifier">default_action</span></code> calls <code class="computeroutput"><span class="identifier">custom_terminal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>. | |
| 43 | </p> | |
| 44 | <p> | |
| 45 | Example: | |
| 46 | </p> | |
| 47 | <pre class="programlisting"><span class="comment">// Call out boost::reference_wrapper for special handling</span> | |
| 48 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> | |
| 49 | <span class="keyword">struct</span> <span class="identifier">is_custom_terminal</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">></span> | |
| 50 | <span class="special">:</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span> | |
| 51 | <span class="special">{};</span> | |
| 52 | ||
| 53 | <span class="comment">// Special handling for boost::reference_wrapper</span> | |
| 54 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> | |
| 55 | <span class="keyword">struct</span> <span class="identifier">custom_terminal</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">></span> | |
| 56 | <span class="special">{</span> | |
| 57 | <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">&</span><span class="identifier">result_type</span><span class="special">;</span> | |
| 58 | ||
| 59 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Context</span><span class="special">></span> | |
| 60 | <span class="identifier">T</span> <span class="special">&</span><span class="keyword">operator</span><span class="special">()(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">reference_wrapper</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">r</span><span class="special">,</span> <span class="identifier">Context</span> <span class="special">&)</span> <span class="keyword">const</span> | |
| 61 | <span class="special">{</span> | |
| 62 | <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span> | |
| 63 | <span class="special">}</span> | |
| 64 | <span class="special">};</span> | |
| 65 | </pre> | |
| 66 | </div> | |
| 67 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 68 | <td align="left"></td> | |
| 69 | <td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas | |
| 70 | Heller, John Fletcher<p> | |
| 71 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 72 | 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>) | |
| 73 | </p> | |
| 74 | </div></td> | |
| 75 | </tr></table> | |
| 76 | <hr> | |
| 77 | <div class="spirit-nav"> | |
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| 79 | </div> | |
| 80 | </body> | |
| 81 | </html> |