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- <title>BOOST_PP_WHILE_d</title>
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- <div style="margin-left: 0px;"> The <b>BOOST_PP_WHILE_<i>d</i></b> macro
- represents a reentry into the <b>BOOST_PP_WHILE</b> looping construct. </div>
- <h4>Usage</h4>
- <div class="code"> <b>BOOST_PP_WHILE_</b> ## <i>d</i>(<i>pred</i>, <i>op</i>,
- <i>state</i>) </div>
- <h4>Arguments</h4>
- <dl>
- <dt>d</dt>
- <dd> The next available <b>BOOST_PP_WHILE</b> iteration. </dd>
- <dt>pred</dt>
- <dd> A binary predicate of the form <i>pred</i>(<i>d</i>, <i>state</i>).
- This predicate is expanded by <b>BOOST_PP_WHILE</b> with the next
- available iteration <i>d</i> and the current <i>state</i>. This
- predicate must expand to value in the range of <i>0</i> to <b>BOOST_PP_LIMIT_MAG</b>.
- The construct continues to loop until this predicate returns <i>0</i>.
- When this predicate returns <i>0</i>, <b>BOOST_PP_WHILE</b> returns
- the current <i>state</i>. </dd>
- <dt>op</dt>
- <dd> A binary operation of the form <i>op</i>(<i>d</i>, <i>state</i>).
- This operation is expanded by <b>BOOST_PP_WHILE</b> with the next
- available iteration <i>d</i> 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>state</dt>
- <dd> The initial state. Often this argument is a <i>tuple</i>. </dd>
- </dl>
- <h4>Remarks</h4>
- <div> This macro iterates <i>op</i>(<i>d</i>, <i>state</i>) while <i>pred</i>(<i>d</i>,
- <i>state</i>) is non-zero. In other words expands to:
- <div> <i>op</i>(<i>d</i>, ... <i>op</i>(<i>d</i>, <i>op</i>(<i>d</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>d</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_WHILE_</b>, <i>d</i>)(<i>pred</i>,
- <i>op</i>, <i>state</i>). </div>
- </div>
- <div> Previously, it was possible to concatenate <i>d</i> directly to <b>BOOST_PP_WHILE</b>
- (without the trailing underscore). This is no longer supported. </div>
- <h4>See Also</h4>
- <ul>
- <li><a href="cat.html">BOOST_PP_CAT</a></li>
- <li><a href="limit_mag.html">BOOST_PP_LIMIT_MAG</a></li>
- <li><a href="while.html">BOOST_PP_WHILE</a></li>
- <li><a href="while_d_macros.html"><span style="color: gray;">Macros with D
- re-entrancy forms</span></a></li>
- </ul>
- <h4>Requirements</h4>
- <div> <b>Header:</b> <a href="../headers/control/while.html"><boost/preprocessor/control/while.hpp></a>
- </div>
- <h4>Sample Code</h4>
- <div>
- <pre>#include <<a href="../headers/arithmetic/add.html">boost/preprocessor/arithmetic/add.hpp</a>>
- #include <<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>>
- #include <<a href="../headers/array/elem.html">boost/preprocessor/array/elem.hpp</a>>
- #include <<a href="../headers/array/size.html">boost/preprocessor/array/size.hpp</a>>
- #include <<a href="../headers/control/while.html">boost/preprocessor/control/while.hpp</a>>
- #include <<a href="../headers/tuple/elem.html">boost/preprocessor/tuple/elem.hpp</a>>
- #define PRED(d, data) <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data)
- #define OP(d, data) \
- OP_D( \
- d, \
- <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 0, data), \
- <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data), \
- <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 2, data) \
- ) \
- /**/
- #define OP_D(d, res, i, array) \
- ( \
- <a href="add_d.html">BOOST_PP_ADD_D</a>( \
- d, res, \
- <a href="array_elem.html">BOOST_PP_ARRAY_ELEM</a>(<a href="dec.html">BOOST_PP_DEC</a>(i), array)), \
- <a href="dec.html">BOOST_PP_DEC</a>(i), \
- array \
- ) \
- /**/
- #define ACCUMULATE_D(d, array) \
- <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>( \
- 3, 0, \
- <a href="while_d.html">BOOST_PP_WHILE_</a> ## d( \
- PRED, OP, \
- (0, <a href="array_size.html">BOOST_PP_ARRAY_SIZE</a>(array), array) \
- ) \
- ) \
- /**/
- #define ARRAY (4, (1, 2, 3, 4))
- ACCUMULATE_D(1, ARRAY)// expands to 10
- </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<br>
- </i><i>© Copyright Edward Diener 2014</i><br>
- </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>
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- </html>
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