list_fold_right.html 2.9 KB

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  2. <head>
  3. <title>BOOST_PP_LIST_FOLD_RIGHT</title>
  4. <link rel="stylesheet" type="text/css" href="../styles.css">
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  6. <body>
  7. <div style="margin-left: 0px;">
  8. The <b>BOOST_PP_LIST_FOLD_RIGHT</b> macro folds (or accumulates) the elements of a <i>list</i> right-to-left.
  9. </div>
  10. <h4>Usage</h4>
  11. <div class="code">
  12. <b>BOOST_PP_LIST_FOLD_RIGHT</b>(<i>op</i>, <i>state</i>, <i>list</i>)
  13. </div>
  14. <h4>Arguments</h4>
  15. <dl>
  16. <dt>op</dt>
  17. <dd>
  18. A ternary operation of the form <i>op</i>(<i>d</i>, <i>state</i>, <i>elem</i>).&nbsp;
  19. This macro is called for each element in <i>list</i>--each time returning a new <i>state</i>.&nbsp;
  20. This operation is expanded by <b>BOOST_PP_LIST_FOLD_RIGHT</b> with the next available <b>BOOST_PP_WHILE</b> iteration,
  21. the current <i>state</i>, and the current element.
  22. </dd>
  23. <dt>state</dt>
  24. <dd>
  25. The initial state of the fold.
  26. </dd>
  27. <dt>list</dt>
  28. <dd>
  29. The <i>list</i> to be folded.
  30. </dd>
  31. </dl>
  32. <h4>Remarks</h4>
  33. <div>
  34. This macro does not have the same signature as it previously did.&nbsp;
  35. The arguments have been swapped to provide a uniform interface with <b>BOOST_PP_LIST_FOLD_LEFT</b>.
  36. </div>
  37. <div>
  38. For the <i>list</i>, (<i>0</i>, (<i>1</i>, (<i>2</i>, <b>BOOST_PP_NIL</b>))), this macro expands to:
  39. <div>
  40. <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>)
  41. </div>
  42. </div>
  43. <div>
  44. Previously, this macro could not be used inside <b>BOOST_PP_WHILE</b>.&nbsp;
  45. There is no longer any such restriction.&nbsp;
  46. It is more efficient, however, to use <b>BOOST_PP_LIST_FOLD_RIGHT_<i>d</i></b> in such a situation.
  47. </div>
  48. <h4>See Also</h4>
  49. <ul>
  50. <li><a href="list_fold_right_d.html">BOOST_PP_LIST_FOLD_RIGHT_<i>d</i></a></li>
  51. </ul>
  52. <h4>Requirements</h4>
  53. <div>
  54. <b>Header:</b> &nbsp;<a href="../headers/list/fold_right.html">&lt;boost/preprocessor/list/fold_right.hpp&gt;</a>
  55. </div>
  56. <h4>Sample Code</h4>
  57. <div><pre>
  58. #include &lt;<a href="../headers/cat.html">boost/preprocessor/cat.hpp</a>&gt;
  59. #include &lt;<a href="../headers/list/fold_right.html">boost/preprocessor/list/fold_right.hpp</a>&gt;
  60. #define LIST (a, (b, (c, <a href="nil.html">BOOST_PP_NIL</a>)))
  61. #define OP(d, state, x) <a href="cat.html">BOOST_PP_CAT</a>(state, x)
  62. <a href="list_fold_right.html">BOOST_PP_LIST_FOLD_RIGHT</a>(OP, _, LIST) // expands to _cba
  63. </pre></div>
  64. <hr size="1">
  65. <div style="margin-left: 0px;">
  66. <i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
  67. </br><i>© Copyright Paul Mensonides 2002</i>
  68. </div>
  69. <div style="margin-left: 0px;">
  70. <p><small>Distributed under the Boost Software License, Version 1.0. (See
  71. accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  72. copy at <a href=
  73. "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
  74. </div>
  75. </body>
  76. </html>