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

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   3         <title>BOOST_PP_LIST_FILTER</title>
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   8                 The <b>BOOST_PP_LIST_FILTER</b> macro filters a <i>list</i> according to a supplied criterion.
   9         </div>
  10         <h4>Usage</h4>
  11                 <div class="code">
  12                         <b>BOOST_PP_LIST_FILTER</b>(<i>pred</i>, <i>data</i>, <i>list</i>)
  13                 </div>
  14         <h4>Arguments</h4>
  15                 <dl>
  16                         <dt>pred</dt>
  17                         <dd>
  18                                 A ternary predicate of the form <i>pred</i>(<i>d</i>, <i>data</i>, <i>elem</i>).&nbsp;
  19                                 This predicate is expanded by <b>BOOST_PP_LIST_FILTER</b> for each element in <i>list</i> with the next available <b>BOOST_PP_WHILE</b> iteration,
  20                                 the auxiliary <i>data</i>, and the current element in <i>list</i>.&nbsp;
  21                                 This macro must return a integral value in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.&nbsp;
  22                                 If this predicate expands to non-zero for a certain element, that element is included in the resulting <i>list</i>.
  23                         </dd>
  24                         <dt>data</dt>
  25                         <dd>
  26                                 Auxiliary data passed to <i>pred</i>.
  27                         </dd>
  28                         <dt>list</dt>
  29                         <dd>
  30                                 The <i>list</i> to be filtered.
  31                         </dd>
  32                 </dl>
  33         <h4>Remarks</h4>
  34                 <div>
  35                         This macro expands <i>pred</i> for each element in <i>list</i>.&nbsp;
  36                         It builds a new <i>list</i> out of each element for which <i>pred</i> returns non-zero.
  37                 </div>
  38                 <div>
  39                         Previously, this macro could not be used inside <b>BOOST_PP_WHILE</b>.&nbsp;
  40                         There is no longer any such restriction.&nbsp;
  41                         It is more efficient, however, to use <b>BOOST_PP_LIST_FILTER_D</b> in such a situation.
  42                 </div>
  43         <h4>See Also</h4>
  44                 <ul>
  45                         <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
  46                         <li><a href="list_filter_d.html">BOOST_PP_LIST_FILTER_D</a></li>
  47                 </ul>
  48         <h4>Requirements</h4>
  49                 <div>
  50                         <b>Header:</b> &nbsp;<a href="../headers/list/filter.html">&lt;boost/preprocessor/list/filter.hpp&gt;</a>
  51                 </div>
  52         <h4>Sample Code</h4>
  53 <div><pre>
  54 #include &lt;<a href="../headers/comparison/less_equal.html">boost/preprocessor/comparison/less_equal.hpp</a>&gt;
  55 #include &lt;<a href="../headers/list/filter.html">boost/preprocessor/list/filter.hpp</a>&gt;
  56
  57 #define LIST (1, (3, (2, (5, <a href="nil.html">BOOST_PP_NIL</a>))))
  58
  59 #define PRED(d, data, elem) <a href="less_equal.html">BOOST_PP_LESS_EQUAL</a>(elem, data)
  60
  61 <a href="list_filter.html">BOOST_PP_LIST_FILTER</a>(PRED, 3, LIST)
  62    // expands to (1, (3, (2, <a href="nil.html">BOOST_PP_NIL</a>)))
  63 </pre></div>
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  66                 <i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
  67                 </br><i>© Copyright Paul Mensonides 2002</i>
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  69         <div style="margin-left: 0px;">
  70                 <p><small>Distributed under the Boost Software License, Version 1.0. (See
  71                 accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  72                 copy at <a href=
  73                 "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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