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<html>
<head>
<title>BOOST_PP_FOR_r</title>
<link rel="stylesheet" type="text/css" href="../styles.css">
<script language="javascript" type="text/javascript" src="../scripts.js"></script>
</head>
<body onload="init('sample');">
<div style="margin-left: 0px;">
The <b>BOOST_PP_FOR_<i>r</i></b> macro represents a reentry into the <b>BOOST_PP_FOR</b> repetition construct.
</div>
<h4>Usage</h4>
<div class="code">
<b>BOOST_PP_FOR_</b> ## <i>r</i>(<i>state</i>, <i>pred</i>, <i>op</i>, <i>macro</i>)
</div>
<h4>Arguments</h4>
<dl>
<dt>r</dt>
<dd>
The next available <b>BOOST_PP_FOR</b> repetition.
</dd>
<dt>state</dt>
<dd>
The initial state.
</dd>
<dt>pred</dt>
<dd>
A binary predicate of the form <i>pred</i>(<i>r</i>, <i>state</i>).&nbsp;
This macro must expand to an integer in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.&nbsp;
<b>BOOST_PP_FOR</b> repeatedly expands <i>macro</i> while this predicate returns non-zero.&nbsp;
This macro is called with the next available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
</dd>
<dt>op</dt>
<dd>
A binary operation of the form <i>op</i>(<i>r</i>, <i>state</i>).&nbsp;
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;
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>.
</dd>
<dt>macro</dt>
<dd>
A binary macro of the form <i>macro</i>(<i>r</i>, <i>state</i>).&nbsp;
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;
This macro is is repeated by <b>BOOST_PP_FOR</b> until <i>pred</i> returns <i>0</i>.
</dd>
</dl>
<h4>Remarks</h4>
<div>
This macro expands to the sequence:
<div>
<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>) ... ))
</div>
</div>
<div>
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;
This happens when the <i>r</i> value is a macro invocation itself.&nbsp;
It needs a delay to allow it to expand.&nbsp;
The syntax in such a scenario becomes:
<div>
<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>)
</div>
</div>
<h4>See Also</h4>
<ul>
<li><a href="cat.html">BOOST_PP_CAT</a></li>
<li><a href="for.html">BOOST_PP_FOR</a></li>
<li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
</ul>
<h4>Requirements</h4>
<div>
<b>Header:</b> &nbsp;<a href="../headers/repetition/for.hpp.html">&lt;boost/preprocessor/repetition/for.hpp&gt;</a>
</div>
<h4><a class="local" onclick="toggle('sample');" onmouseover="change(this);" onmouseout="revert(this);">Sample Code</a></h4>
<div id="sample"><pre>
#include &lt;boost/preprocessor/arithmetic/dec.hpp&gt;
#include &lt;boost/preprocessor/arithmetic/inc.hpp&gt;
#include &lt;boost/preprocessor/comparison/not_equal.hpp&gt;
#include &lt;boost/preprocessor/punctuation/comma_if.hpp&gt;
#include &lt;boost/preprocessor/repetition/for.hpp&gt;
#include &lt;boost/preprocessor/tuple/elem.hpp&gt;
#define PRED(r, state) /* ............ */ \
BOOST_PP_NOT_EQUAL( \
BOOST_PP_TUPLE_ELEM(4, 0, state), \
BOOST_PP_INC( \
BOOST_PP_TUPLE_ELEM(4, 1, state) \
) \
) \
/**/
#define OP(r, state) /* .............. */ \
( \
BOOST_PP_INC( \
BOOST_PP_TUPLE_ELEM(4, 0, state) \
), \
BOOST_PP_TUPLE_ELEM(4, 1, state), \
BOOST_PP_TUPLE_ELEM(4, 2, state), \
BOOST_PP_INC( \
BOOST_PP_TUPLE_ELEM(4, 3, state) \
) \
) \
/**/
#define MACRO(r, state) /* ....................... */ \
BOOST_PP_COMMA_IF( \
BOOST_PP_TUPLE_ELEM(4, 3, state) \
) template&lt; \
BOOST_PP_FOR_ ## r( \
(0, BOOST_PP_TUPLE_ELEM(4, 0, state), _, 0), \
PRED_2, OP, MACRO_2 \
) \
&gt; class BOOST_PP_CAT( \
BOOST_PP_TUPLE_ELEM(4, 2, state), \
BOOST_PP_TUPLE_ELEM(4, 0, state) \
) \
/**/
#define PRED_2(r, state) /* ........ */ \
BOOST_PP_NOT_EQUAL( \
BOOST_PP_TUPLE_ELEM(4, 0, state), \
BOOST_PP_TUPLE_ELEM(4, 1, state) \
) \
/**/
#define MACRO_2(r, state) /* ...... */ \
BOOST_PP_COMMA_IF( \
BOOST_PP_TUPLE_ELEM(4, 0, state) \
) class \
/**/
#define TEMPLATE_TEMPLATE(low, high, name) /* ... */ \
BOOST_PP_FOR( \
(low, high, name, 0), \
PRED, OP, MACRO \
) \
/**/
TEMPLATE_TEMPLATE(2, 4, T)
/*
expands to...
template&lt;class, class&gt; class T2,
template&lt;class, class, class&gt; class T3,
template&lt;class, class, class, class&gt; class T4
*/
<pre></div>
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