ceph/src/boost/libs/phoenix/doc/html/phoenix/inside/placeholder_unification.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>Placeholder Unification</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&#160;1.&#160;Phoenix 3.2.0">
   8 <link rel="up" href="../inside.html" title="Inside Phoenix">
   9 <link rel="prev" href="custom_terminals.html" title="Custom Terminals">
  10 <link rel="next" href="../examples.html" title="Advanced Examples">
  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 href="../../../../../../libs/libraries.htm">Libraries</a></td>
  17 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  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="custom_terminals.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="../examples.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.placeholder_unification"></a><a class="link" href="placeholder_unification.html" title="Placeholder Unification">Placeholder Unification</a>
  28 </h3></div></div></div>
  29 <p>
  30         Phoenix uses <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_placeholder</span></code> for recognizing placeholders:
  31       </p>
  32 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">&gt;</span>
  33 <span class="keyword">struct</span> <span class="identifier">is_placeholder</span>
  34 <span class="special">{</span>
  35     <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">value</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
  36 <span class="special">};</span>
  37 </pre>
  38 <p>
  39         To adapt your own placeholder, the nested value needs to be greater than
  40         0 for your types. This is done by specializing this trait.
  41       </p>
  42 </div>
  43 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
  44 <td align="left"></td>
  45 <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas
  46       Heller, John Fletcher<p>
  47         Distributed under the Boost Software License, Version 1.0. (See accompanying
  48         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>)
  49       </p>
  50 </div></td>
  51 </tr></table>
  52 <hr>
  53 <div class="spirit-nav">
  54 <a accesskey="p" href="custom_terminals.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="../examples.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
  55 </div>
  56 </body>
  57 </html>