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<html>
<head>
<title>BOOST_PP_FOR_r</title>
<link rel="stylesheet" type="text/css" href="../styles.css">
</head>
<body>
<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>).
This macro must expand to an integer in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.
<b>BOOST_PP_FOR</b> repeatedly expands <i>macro</i> while this predicate returns non-zero.
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>).
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>.
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>).
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>.
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.
This happens when the <i>r</i> value is a macro invocation itself.
It needs a delay to allow it to expand.
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> <a href="../headers/repetition/for.html"><boost/preprocessor/repetition/for.hpp></a>
</div>
<h4>Sample Code</h4>
<div><pre>
#include <<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>>
#include <<a href="../headers/arithmetic/inc.html">boost/preprocessor/arithmetic/inc.hpp</a>>
#include <<a href="../headers/comparison/not_equal.html">boost/preprocessor/comparison/not_equal.hpp</a>>
#include <<a href="../headers/punctuation/comma_if.html">boost/preprocessor/punctuation/comma_if.hpp</a>>
#include <<a href="../headers/repetition/for.html">boost/preprocessor/repetition/for.hpp</a>>
#include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>>
#define PRED(r, state) \
<a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
<a href="inc.html">BOOST_PP_INC</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
) \
) \
/**/
#define OP(r, state) \
( \
<a href="inc.html">BOOST_PP_INC</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
), \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state), \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
<a href="inc.html">BOOST_PP_INC</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
) \
) \
/**/
#define MACRO(r, state) \
<a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
) template< \
<a href="for_r.html">BOOST_PP_FOR_</a> ## r( \
(0, <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), _, 0), \
PRED_2, OP, MACRO_2 \
) \
> class <a href="cat.html">BOOST_PP_CAT</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
) \
/**/
#define PRED_2(r, state) \
<a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
) \
/**/
#define MACRO_2(r, state) \
<a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
) class \
/**/
#define TEMPLATE_TEMPLATE(low, high, name) \
<a href="for.html">BOOST_PP_FOR</a>( \
(low, high, name, 0), \
PRED, OP, MACRO \
) \
/**/
TEMPLATE_TEMPLATE(2, 4, T)
/*
expands to...
template<class, class> class T2,
template<class, class, class> class T3,
template<class, class, class, class> class T4
*/
</pre></div>
<hr size="1">
<div style="margin-left: 0px;">
<i> Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
</br><i> Copyright Paul Mensonides 2002</i>
</div>
<div style="margin-left: 0px;">
<p><small>Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
copy at <a href=
"http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
</div>
</body>
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