ceph/src/boost/libs/preprocessor/doc/ref/expand.html

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   3         <title>BOOST_PP_EXPAND</title>
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   8                 The <b>BOOST_PP_EXPAND</b> macro performs a double macro-expansion on its argument.
   9         </div>
  10         <h4>Usage</h4>
  11                 <div class="code">
  12                         <b>BOOST_PP_EXPAND</b>(<i>x</i>)
  13                 </div>
  14         <h4>Arguments</h4>
  15                 <dl>
  16                         <dt>x</dt>
  17                         <dd>
  18                                 The argument to be expanded twice.
  19                         </dd>
  20                 </dl>
  21         <h4>Remarks</h4>
  22                 <div>
  23                         This macro is useful when a delay is necessary to produce the correct semantics of a macro invocation.&nbsp;
  24                         For example, when a macro expands to an argument list to another macro.&nbsp;
  25                         This macro will expand the the argument list on the first pass, and then rescan to expand any more macros.
  26                 </div>
  27         <h4>Requirements</h4>
  28                 <div>
  29                         <b>Header:</b> &nbsp;<a href="../headers/facilities/expand.html">&lt;boost/preprocessor/facilities/expand.hpp&gt;</a>
  30                 </div>
  31         <h4>Sample Code</h4>
  32 <div><pre>
  33 #include &lt;<a href="../headers/control/if.html">boost/preprocessor/control/if.hpp</a>&gt;
  34 #include &lt;<a href="../headers/facilities/expand.html">boost/preprocessor/facilities/expand.hpp</a>&gt;
  35
  36 #define MACRO(a, b, c) (a)(b)(c)
  37 #define ARGS() (1, 2, 3)
  38
  39 <a href="expand.html">BOOST_PP_EXPAND</a>(MACRO ARGS()) // expands to (1)(2)(3)
  40
  41 #define SAMPLE(n) \
  42    <a href="expand.html">BOOST_PP_EXPAND</a>( \
  43       MACRO \
  44       <a href="if.html">BOOST_PP_IF</a>( \
  45          n, \
  46          (x, y, z), \
  47          (a, b, c) \
  48       ) \
  49    ) \
  50    /**/
  51
  52 SAMPLE(0) // expands to (a)(b)(c)
  53 SAMPLE(1) // expands to (x)(y)(z)
  54 </pre></div>
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  56         <div style="margin-left: 0px;">
  57                 <i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
  58                 </br><i>© Copyright Paul Mensonides 2002</i>
  59         </div>
  60         <div style="margin-left: 0px;">
  61                 <p><small>Distributed under the Boost Software License, Version 1.0. (See
  62                 accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  63                 copy at <a href=
  64                 "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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