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2 <head>
3 <meta content="text/html; charset=windows-1252" http-equiv="content-type">
4 <title>BOOST_PP_FOR_r</title>
5 <link rel="stylesheet" type="text/css" href="../styles.css">
6 </head>
7 <body>
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
128TEMPLATE_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>
136 <hr size="1">
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>
146 </div>
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