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70 lines
2.5 KiB
HTML
70 lines
2.5 KiB
HTML
<html>
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<head>
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<title>BOOST_PP_LIST_FOLD_RIGHT</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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<script language="javascript" type="text/javascript" src="../scripts.js"></script>
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</head>
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<body onload="init('sample');">
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<div style="margin-left: 0px;">
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The <b>BOOST_PP_LIST_FOLD_RIGHT</b> macro folds (or accumulates) the elements of a <i>list</i> right-to-left.
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</div>
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<h4>Usage</h4>
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<div class="code">
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<b>BOOST_PP_LIST_FOLD_RIGHT</b>(<i>op</i>, <i>state</i>, <i>list</i>)
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</div>
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<h4>Arguments</h4>
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<dl>
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<dt>op</dt>
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<dd class="incompatibility">
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A ternary operation of the form <i>op</i>(<i>d</i>, <i>state</i>, <i>elem</i>).
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This macro is called for each element in <i>list</i>--each time returning a new <i>state</i>.
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This operation is expanded by <b>BOOST_PP_LIST_FOLD_RIGHT</b> with the next available <b>BOOST_PP_WHILE</b> iteration,
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the current <i>state</i>, and the current element.
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</dd>
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<dt>state</dt>
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<dd>
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The initial state of the fold.
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</dd>
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<dt>list</dt>
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<dd>
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The <i>list</i> to be folded.
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</dd>
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</dl>
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<h4>Remarks</h4>
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<div class="incompatibility">
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This macro does not have the same signature as it previously did.
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The arguments have been swapped to provide a uniform interface with <b>BOOST_PP_LIST_FOLD_LEFT</b>.
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</div>
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<div>
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For the <i>list</i>, (<i>0</i>, (<i>1</i>, (<i>2</i>, <b>BOOST_PP_NIL</b>))), this macro expands to:
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<div class="incompatibility">
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<i>op</i>(<i>d</i>, <i>op</i>(<i>d</i>, <i>op</i>(<i>d</i>, <i>state</i>, <i>2</i>), <i>1</i>), <i>0</i>)
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</div>
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</div>
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<div>
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Previously, this macro could not be used inside <b>BOOST_PP_WHILE</b>.
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There is no longer any such restriction.
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It is more efficient, however, to use <b>BOOST_PP_LIST_FOLD_RIGHT_<i>d</i></b> in such a situation.
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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="list_fold_right_d.html">BOOST_PP_LIST_FOLD_RIGHT_<i>d</i></a></li>
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</ul>
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<h4>Requirements</h4>
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<div>
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<b>Header:</b> <a href="../headers/list/fold_right.hpp.html"><boost/preprocessor/list/fold_right.hpp></a>
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</div>
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<h4><a class="local" onclick="toggle('sample');" onmouseover="change(this);" onmouseout="revert(this);">Sample Code</a></h4>
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<div id="sample"><pre>
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#include <boost/preprocessor/cat.hpp>
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#include <boost/preprocessor/list/fold_right.hpp>
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#define LIST (a, (b, (c, BOOST_PP_NIL)))
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#define OP(d, state, x) BOOST_PP_CAT(state, x)
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BOOST_PP_LIST_FOLD_RIGHT(OP, _, LIST) // expands to _cba
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<pre></div>
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</body>
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</html>
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