libs/preprocessor/doc/ref/for_r.html

   1 <html>
   2 <head>
   3         <title>BOOST_PP_FOR_r</title>
   4         <link rel="stylesheet" type="text/css" href="../styles.css">
   5 </head>
   6 <body>
   7         <div style="margin-left:  0px;">
   8                 The <b>BOOST_PP_FOR_<i>r</i></b> macro represents a reentry into the <b>BOOST_PP_FOR</b> repetition construct.
   9         </div>
  10         <h4>Usage</h4>
  11                 <div class="code">
  12                         <b>BOOST_PP_FOR_</b> ## <i>r</i>(<i>state</i>, <i>pred</i>, <i>op</i>, <i>macro</i>)
  13                 </div>
  14         <h4>Arguments</h4>
  15                 <dl>
  16                         <dt>r</dt>
  17                         <dd>
  18                                 The next available <b>BOOST_PP_FOR</b> repetition.
  19                         </dd>
  20                         <dt>state</dt>
  21                         <dd>
  22                                 The initial state.
  23                         </dd>
  24                         <dt>pred</dt>
  25                         <dd>
  26                                 A binary predicate of the form <i>pred</i>(<i>r</i>, <i>state</i>).&nbsp;
  27                                 This macro must expand to an integer in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.&nbsp;
  28                                 <b>BOOST_PP_FOR</b> repeatedly expands <i>macro</i> while this predicate returns non-zero.&nbsp;
  29                                 This macro is called with the next available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
  30                         </dd>
  31                         <dt>op</dt>
  32                         <dd>
  33                                 A binary operation of the form <i>op</i>(<i>r</i>, <i>state</i>).&nbsp;
  34                                 This operation is expanded by <b>BOOST_PP_FOR</b> with the next available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.&nbsp;
  35                                 This macro is repeatedly applied to the <i>state</i>, each time producing a new <i>state</i>, until <i>pred</i> returns <i>0</i>.
  36                         </dd>
  37                         <dt>macro</dt>
  38                         <dd>
  39                                 A binary macro of the form <i>macro</i>(<i>r</i>, <i>state</i>).&nbsp;
  40                                 This macro is expanded by <b>BOOST_PP_FOR</b> with the next available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.&nbsp;
  41                                 This macro is is repeated by <b>BOOST_PP_FOR</b> until <i>pred</i> returns <i>0</i>.
  42                         </dd>
  43                 </dl>
  44         <h4>Remarks</h4>
  45                 <div>
  46                         This macro expands to the sequence:
  47                         <div>
  48                                 <i>macro</i>(<i>r</i>, <i>state</i>) <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>, <i>state</i>)) ... <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>, ... <i>op</i>(<i>r</i>, <i>state</i>) ... ))
  49                         </div>
  50                 </div>
  51                 <div>
  52                         At certain times, it may be necessary to perform the concatenation with <b>BOOST_PP_CAT</b> rather than the preprocessor token-pasting operator.&nbsp;
  53                         This happens when the <i>r</i> value is a macro invocation itself.&nbsp;
  54                         It needs a delay to allow it to expand.&nbsp;
  55                         The syntax in such a scenario becomes:
  56                         <div>
  57                                 <b>BOOST_PP_CAT</b>(<b>BOOST_PP_FOR_</b>, <i>r</i>)(<i>state</i>, <i>pred</i>, <i>op</i>, <i>macro</i>)
  58                         </div>
  59                 </div>
  60         <h4>See Also</h4>
  61                 <ul>
  62                         <li><a href="cat.html">BOOST_PP_CAT</a></li>
  63                         <li><a href="for.html">BOOST_PP_FOR</a></li>
  64                         <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
  65                 </ul>
  66         <h4>Requirements</h4>
  67                 <div>
  68                         <b>Header:</b> &nbsp;<a href="../headers/repetition/for.html">&lt;boost/preprocessor/repetition/for.hpp&gt;</a>
  69                 </div>
  70         <h4>Sample Code</h4>
  71 <div><pre>
  72 #include &lt;<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>&gt;
  73 #include &lt;<a href="../headers/arithmetic/inc.html">boost/preprocessor/arithmetic/inc.hpp</a>&gt;
  74 #include &lt;<a href="../headers/comparison/not_equal.html">boost/preprocessor/comparison/not_equal.hpp</a>&gt;
  75 #include &lt;<a href="../headers/punctuation/comma_if.html">boost/preprocessor/punctuation/comma_if.hpp</a>&gt;
  76 #include &lt;<a href="../headers/repetition/for.html">boost/preprocessor/repetition/for.hpp</a>&gt;
  77 #include &lt;<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>&gt;
  78
  79 #define PRED(r, state) \
  80    <a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
  81       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
  82       <a href="inc.html">BOOST_PP_INC</a>( \
  83          <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
  84       ) \
  85    ) \
  86    /**/
  87
  88 #define OP(r, state) \
  89    ( \
  90       <a href="inc.html">BOOST_PP_INC</a>( \
  91          <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
  92       ), \
  93       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state), \
  94       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
  95       <a href="inc.html">BOOST_PP_INC</a>( \
  96          <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
  97       ) \
  98    ) \
  99    /**/
 100
 101 #define MACRO(r, state) \
 102    <a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
 103       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
 104    ) template&lt; \
 105       <a href="for_r.html">BOOST_PP_FOR_</a> ## r( \
 106          (0, <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), _, 0), \
 107          PRED_2, OP, MACRO_2 \
 108       ) \
 109    &gt; class <a href="cat.html">BOOST_PP_CAT</a>( \
 110       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
 111       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
 112    ) \
 113    /**/
 114
 115 #define PRED_2(r, state) \
 116    <a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
 117       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
 118       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
 119    ) \
 120    /**/
 121
 122 #define MACRO_2(r, state) \
 123    <a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
 124       <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
 125    ) class \
 126    /**/
 127
 128 #define TEMPLATE_TEMPLATE(low, high, name) \
 129    <a href="for.html">BOOST_PP_FOR</a>( \
 130       (low, high, name, 0), \
 131       PRED, OP, MACRO \
 132    ) \
 133    /**/
 134
 135 TEMPLATE_TEMPLATE(2, 4, T)
 136 /*
 137    expands to...
 138    template&lt;class, class&gt; class T2,
 139    template&lt;class, class, class&gt; class T3,
 140    template&lt;class, class, class, class&gt; class T4
 141 */
 142 </pre></div>
 143         <hr size="1">
 144         <div style="margin-left: 0px;">
 145                 <i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
 146                 </br><i>© Copyright Paul Mensonides 2002</i>
 147         </div>
 148         <div style="margin-left: 0px;">
 149                 <p><small>Distributed under the Boost Software License, Version 1.0. (See
 150                 accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
 151                 copy at <a href=
 152                 "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
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 155 </html>