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

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   3         <title>BOOST_PP_IDENTITY_N</title>
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   8             The <b>BOOST_PP_IDENTITY_N</b> macro expands to its first argument when invoked.
   9         </div>
  10         <h4>Usage</h4>
  11                 <div class="code">
  12                         <b>BOOST_PP_IDENTITY_N</b>(<i>item,n</i>)(n-arguments)
  13                 </div>
  14         <h4>Arguments</h4>
  15                 <dl>
  16                         <dt>item</dt>
  17                         <dd>
  18                                 The result of the expansion.
  19                         </dd>
  20                         <dt>n</dt>
  21                         <dd>
  22                                 The number of arguments when invoked.
  23                         </dd>
  24                 </dl>
  25         <h4>Remarks</h4>
  26                 <div>
  27                         This macro is designed to be used with <b>BOOST_PP_IF</b> and <b>BOOST_PP_IIF</b> when only one of the clauses needs to be invoked.
  28                 </div>
  29         <h4>See Also</h4>
  30                 <ul>
  31                         <li><a href="if.html">BOOST_PP_IF</a></li>
  32                         <li><a href="iif.html">BOOST_PP_IIF</a></li>
  33                 </ul>
  34         <h4>Requirements</h4>
  35                 <div>
  36                         <b>Header:</b> &nbsp;<a href="../headers/facilities/identity_n.html">&lt;boost/preprocessor/facilities/identity.hpp&gt;</a>
  37                 </div>
  38         <h4>Sample Code</h4>
  39 <div><pre>
  40 #include &lt;<a href="../headers/control/if.html">boost/preprocessor/control/if.hpp</a>&gt;
  41 #include &lt;<a href="../headers/facilities/identity.html">boost/preprocessor/facilities/identity.hpp</a>&gt;
  42
  43 #define MACRO_CAT(y,z) y ## z
  44 #define MACRO(n) <a href="if.html">BOOST_PP_IF</a>(n, <a href="identity_n.html">BOOST_PP_IDENTITY_N</a>(x,2), MACRO_CAT)(a,b)
  45
  46 MACRO(0) // expands to ab
  47 MACRO(1) // expands to x
  48 </pre></div>
  49         <hr size="1">
  50     <div style="margin-left: 0px"><i>&copy; Copyright Edward Diener 2015</i></div>
  51         <div style="margin-left: 0px;">
  52                 <p><small>Distributed under the Boost Software License, Version 1.0. (See
  53                 accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  54                 copy at <a href=
  55                 "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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