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

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   8     <div style="margin-left:  0px;"> The <b>BOOST_PP_FOR_<i>r</i></b> macro
   9       represents a reentry into the <b>BOOST_PP_FOR</b> repetition construct. </div>
  10     <h4>Usage</h4>
  11     <div class="code"> <b>BOOST_PP_FOR_</b> ## <i>r</i>(<i>state</i>, <i>pred</i>,
  12       <i>op</i>, <i>macro</i>) </div>
  13     <h4>Arguments</h4>
  14     <dl>
  15       <dt>r</dt>
  16       <dd> The next available <b>BOOST_PP_FOR</b> repetition. </dd>
  17       <dt>state</dt>
  18       <dd> The initial state. </dd>
  19       <dt>pred</dt>
  20       <dd> A binary predicate of the form <i>pred</i>(<i>r</i>, <i>state</i>).&nbsp;
  21         This macro must expand to an integer in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.&nbsp;
  22         <b>BOOST_PP_FOR</b> repeatedly expands <i>macro</i> while this
  23         predicate returns non-zero.&nbsp; This macro is called with the next
  24         available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
  25       </dd>
  26       <dt>op</dt>
  27       <dd> A binary operation of the form <i>op</i>(<i>r</i>, <i>state</i>).&nbsp;
  28         This operation is expanded by <b>BOOST_PP_FOR</b> with the next
  29         available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.&nbsp;
  30         This macro is repeatedly applied to the <i>state</i>, each time
  31         producing a new <i>state</i>, until <i>pred</i> returns <i>0</i>. </dd>
  32       <dt>macro</dt>
  33       <dd> A binary macro of the form <i>macro</i>(<i>r</i>, <i>state</i>).&nbsp;
  34         This macro is expanded by <b>BOOST_PP_FOR</b> with the next available <b>BOOST_PP_FOR</b>
  35         repetition and the current <i>state</i>.&nbsp; This macro is is
  36         repeated by <b>BOOST_PP_FOR</b> until <i>pred</i> returns <i>0</i>. </dd>
  37     </dl>
  38     <h4>Remarks</h4>
  39     <div> This macro expands to the sequence:
  40       <div> <i>macro</i>(<i>r</i>, <i>state</i>) <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>,
  41         <i>state</i>)) ... <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>, ... <i>op</i>(<i>r</i>,
  42         <i>state</i>) ... )) </div>
  43     </div>
  44     <div> At certain times, it may be necessary to perform the concatenation
  45       with <b>BOOST_PP_CAT</b> rather than the preprocessor token-pasting
  46       operator.&nbsp; This happens when the <i>r</i> value is a macro
  47       invocation itself.&nbsp; It needs a delay to allow it to expand.&nbsp; The
  48       syntax in such a scenario becomes:
  49       <div> <b>BOOST_PP_CAT</b>(<b>BOOST_PP_FOR_</b>, <i>r</i>)(<i>state</i>,
  50         <i>pred</i>, <i>op</i>, <i>macro</i>) </div>
  51     </div>
  52     <h4>See Also</h4>
  53     <ul>
  54       <li><a href="cat.html">BOOST_PP_CAT</a></li>
  55       <li><a href="for.html">BOOST_PP_FOR</a></li>
  56       <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
  57       <li><a href="for_r_macros.html"><span style="color: gray;">Macros with R
  58             re-entrancy forms</span></a></li>
  59     </ul>
  60     <h4>Requirements</h4>
  61     <div> <b>Header:</b> &nbsp;<a href="../headers/repetition/for.html">&lt;boost/preprocessor/repetition/for.hpp&gt;</a>
  62     </div>
  63     <h4>Sample Code</h4>
  64     <div>
  65       <pre>#include &lt;<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>&gt;
  66 #include &lt;<a href="../headers/arithmetic/inc.html">boost/preprocessor/arithmetic/inc.hpp</a>&gt;
  67 #include &lt;<a href="../headers/comparison/not_equal.html">boost/preprocessor/comparison/not_equal.hpp</a>&gt;
  68 #include &lt;<a href="../headers/punctuation/comma_if.html">boost/preprocessor/punctuation/comma_if.hpp</a>&gt;
  69 #include &lt;<a href="../headers/repetition/for.html">boost/preprocessor/repetition/for.hpp</a>&gt;
  70 #include &lt;<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>&gt;
  71
  72 #define PRED(r, state) \
  73    <a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
  74       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
  75       <a href="inc.html">BOOST_PP_INC</a>( \
  76          <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
  77       ) \
  78    ) \
  79    /**/
  80
  81 #define OP(r, state) \
  82    ( \
  83       <a href="inc.html">BOOST_PP_INC</a>( \
  84          <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
  85       ), \
  86       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state), \
  87       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
  88       <a href="inc.html">BOOST_PP_INC</a>( \
  89          <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
  90       ) \
  91    ) \
  92    /**/
  93
  94 #define MACRO(r, state) \
  95    <a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
  96       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
  97    ) template&lt; \
  98       <a href="for_r.html">BOOST_PP_FOR_</a> ## r( \
  99          (0, <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), _, 0), \
 100          PRED_2, OP, MACRO_2 \
 101       ) \
 102    &gt; class <a href="cat.html">BOOST_PP_CAT</a>( \
 103       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
 104       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
 105    ) \
 106    /**/
 107
 108 #define PRED_2(r, state) \
 109    <a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
 110       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
 111       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
 112    ) \
 113    /**/
 114
 115 #define MACRO_2(r, state) \
 116    <a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
 117       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
 118    ) class \
 119    /**/
 120
 121 #define TEMPLATE_TEMPLATE(low, high, name) \
 122    <a href="for.html">BOOST_PP_FOR</a>( \
 123       (low, high, name, 0), \
 124       PRED, OP, MACRO \
 125    ) \
 126    /**/
 127
 128 TEMPLATE_TEMPLATE(2, 4, T)
 129 /*
 130    expands to...
 131    template&lt;class, class&gt; class T2,
 132    template&lt;class, class, class&gt; class T3,
 133    template&lt;class, class, class, class&gt; class T4
 134 */
 135 </pre></div>
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 137     <div style="margin-left: 0px;"> <i>© Copyright <a href="http://www.housemarque.com"
 138           target="_top">Housemarque Oy</a> 2002</i> <br>
 139       <i>© Copyright Paul Mensonides 2002<br>
 140       </i><i>© Copyright Edward Diener 2014</i><br>
 141     </div>
 142     <div style="margin-left: 0px;">
 143       <p><small>Distributed under the Boost Software License, Version 1.0. (See
 144           accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
 145           or copy at <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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