149 lines
6.4 KiB
HTML
149 lines
6.4 KiB
HTML
<html>
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<head>
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<meta content="text/html; charset=windows-1252" http-equiv="content-type">
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<title>BOOST_PP_FOR_r</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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</head>
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<body>
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<div style="margin-left: 0px;"> The <b>BOOST_PP_FOR_<i>r</i></b> macro
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represents a reentry into the <b>BOOST_PP_FOR</b> repetition construct. </div>
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<h4>Usage</h4>
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<div class="code"> <b>BOOST_PP_FOR_</b> ## <i>r</i>(<i>state</i>, <i>pred</i>,
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<i>op</i>, <i>macro</i>) </div>
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<h4>Arguments</h4>
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<dl>
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<dt>r</dt>
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<dd> The next available <b>BOOST_PP_FOR</b> repetition. </dd>
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<dt>state</dt>
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<dd> The initial state. </dd>
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<dt>pred</dt>
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<dd> A binary predicate of the form <i>pred</i>(<i>r</i>, <i>state</i>).
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This macro must expand to an integer in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.
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<b>BOOST_PP_FOR</b> repeatedly expands <i>macro</i> while this
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predicate returns non-zero. This macro is called with the next
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available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
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</dd>
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<dt>op</dt>
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<dd> A binary operation of the form <i>op</i>(<i>r</i>, <i>state</i>).
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This operation is expanded by <b>BOOST_PP_FOR</b> with the next
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available <b>BOOST_PP_FOR</b> repetition and the current <i>state</i>.
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This macro is repeatedly applied to the <i>state</i>, each time
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producing a new <i>state</i>, until <i>pred</i> returns <i>0</i>. </dd>
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<dt>macro</dt>
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<dd> A binary macro of the form <i>macro</i>(<i>r</i>, <i>state</i>).
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This macro is expanded by <b>BOOST_PP_FOR</b> with the next available <b>BOOST_PP_FOR</b>
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repetition and the current <i>state</i>. This macro is is
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repeated by <b>BOOST_PP_FOR</b> until <i>pred</i> returns <i>0</i>. </dd>
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</dl>
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<h4>Remarks</h4>
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<div> This macro expands to the sequence:
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<div> <i>macro</i>(<i>r</i>, <i>state</i>) <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>,
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<i>state</i>)) ... <i>macro</i>(<i>r</i>, <i>op</i>(<i>r</i>, ... <i>op</i>(<i>r</i>,
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<i>state</i>) ... )) </div>
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</div>
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<div> At certain times, it may be necessary to perform the concatenation
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with <b>BOOST_PP_CAT</b> rather than the preprocessor token-pasting
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operator. This happens when the <i>r</i> value is a macro
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invocation itself. It needs a delay to allow it to expand. The
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syntax in such a scenario becomes:
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<div> <b>BOOST_PP_CAT</b>(<b>BOOST_PP_FOR_</b>, <i>r</i>)(<i>state</i>,
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<i>pred</i>, <i>op</i>, <i>macro</i>) </div>
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</div>
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<h4>See Also</h4>
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<ul>
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<li><a href="cat.html">BOOST_PP_CAT</a></li>
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<li><a href="for.html">BOOST_PP_FOR</a></li>
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<li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
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<li><a href="for_r_macros.html"><span style="color: gray;">Macros with R
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re-entrancy forms</span></a></li>
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</ul>
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<h4>Requirements</h4>
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<div> <b>Header:</b> <a href="../headers/repetition/for.html"><boost/preprocessor/repetition/for.hpp></a>
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</div>
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<h4>Sample Code</h4>
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<div>
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<pre>#include <<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>>
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#include <<a href="../headers/arithmetic/inc.html">boost/preprocessor/arithmetic/inc.hpp</a>>
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#include <<a href="../headers/comparison/not_equal.html">boost/preprocessor/comparison/not_equal.hpp</a>>
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#include <<a href="../headers/punctuation/comma_if.html">boost/preprocessor/punctuation/comma_if.hpp</a>>
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#include <<a href="../headers/repetition/for.html">boost/preprocessor/repetition/for.hpp</a>>
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#include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>>
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#define PRED(r, state) \
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<a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
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<a href="inc.html">BOOST_PP_INC</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
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) \
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) \
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/**/
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#define OP(r, state) \
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( \
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<a href="inc.html">BOOST_PP_INC</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
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), \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state), \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
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<a href="inc.html">BOOST_PP_INC</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
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) \
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) \
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/**/
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#define MACRO(r, state) \
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<a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 3, state) \
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) template< \
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<a href="for_r.html">BOOST_PP_FOR_</a> ## r( \
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(0, <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), _, 0), \
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PRED_2, OP, MACRO_2 \
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) \
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> class <a href="cat.html">BOOST_PP_CAT</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 2, state), \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
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) \
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/**/
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#define PRED_2(r, state) \
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<a href="not_equal.html">BOOST_PP_NOT_EQUAL</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state), \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 1, state) \
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) \
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/**/
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#define MACRO_2(r, state) \
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<a href="comma_if.html">BOOST_PP_COMMA_IF</a>( \
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<a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(4, 0, state) \
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) class \
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/**/
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#define TEMPLATE_TEMPLATE(low, high, name) \
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<a href="for.html">BOOST_PP_FOR</a>( \
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(low, high, name, 0), \
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PRED, OP, MACRO \
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) \
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/**/
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TEMPLATE_TEMPLATE(2, 4, T)
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/*
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expands to...
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template<class, class> class T2,
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template<class, class, class> class T3,
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template<class, class, class, class> class T4
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*/
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</pre></div>
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<hr size="1">
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<div style="margin-left: 0px;"> <i><EFBFBD> Copyright <a href="http://www.housemarque.com"
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target="_top">Housemarque Oy</a> 2002</i> <br>
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<i><EFBFBD> Copyright Paul Mensonides 2002<br>
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</i><i><EFBFBD> Copyright Edward Diener 2014</i><br>
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</div>
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<div style="margin-left: 0px;">
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<p><small>Distributed under the Boost Software License, Version 1.0. (See
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accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
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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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</div>
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</body>
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</html>
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