ceph/src/boost/libs/preprocessor/doc/data/sequences.html

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   8     <h4> Sequences </h4>
   9     <div> A <i>sequence</i> (abbreviated to <i>seq</i>) is a group of adjacent
  10       parenthesized elements. For example, </div>
  11     <div class="code"> (<i>a</i>)(<i>b</i>)(<i>c</i>) </div>
  12     <div> ...is a <i>seq</i> of <i>3</i> elements--<i>a</i>, <i>b</i>, and <i>c</i>.
  13     </div>
  14     <div> <i>Sequences</i> are data structures that merge the properties of
  15       both <i>lists</i> and <i>tuples</i> with the exception that a <i>seq, </i>like
  16       a <i>tuple, </i>cannot be empty.&nbsp; Therefore, an "empty" <i>seq</i>
  17       is considered a special case scenario that must be handled separately in
  18       C++. </div>
  19     <div class="code">
  20       <pre>#define SEQ (x)(y)(z)
  21 #define REVERSE(s, state, elem) (elem) state
  22    // append to head                  ^
  23
  24 BOOST_PP_SEQ_FOLD_LEFT(REVERSE, BOOST_PP_EMPTY, SEQ)()
  25    //                           #1                  #2
  26    // 1) placeholder for "empty" seq
  27    // 2) remove placeholder
  28
  29 #define SEQ_B (1)(2)(3)
  30 #define INC(s, state, elem) state (BOOST_PP_INC(elem))
  31    // append to tail             ^
  32
  33 BOOST_PP_SEQ_FOLD_RIGHT(INC, BOOST_PP_SEQ_NIL, SEQ)
  34    //                        ^
  35    // special placeholder that will be "eaten"
  36    // by appending to the tail
  37 </pre> </div>
  38     <div> <i>Sequences</i> are extremely efficient.&nbsp; Element access speed
  39       approaches random access--even with <i>seqs</i> of up to <i>256</i>
  40       elements.&nbsp; This is because element access (among other things) is
  41       implemented iteratively rather than recursively.&nbsp; Therefore, elements
  42       can be accessed at extremely high indices even on preprocessors with low
  43       maximum expansion depths. </div>
  44     <div> Elements of a <i>seq</i> can be extracted with <b>BOOST_PP_SEQ_ELEM</b>.
  45     </div>
  46     <h4> Primitives </h4>
  47     <ul>
  48       <li> <a href="../ref/seq_elem.html">BOOST_PP_SEQ_ELEM</a></li>
  49     </ul>
  50     <hr size="1">
  51     <div style="margin-left: 0px;"> <i>© Copyright <a href="http://www.housemarque.com"
  52           target="_top">Housemarque Oy</a> 2002</i> <br>
  53       <i>© Copyright Paul Mensonides 2002</i> </div>
  54     <div style="margin-left: 0px;">
  55       <p><small>Distributed under the Boost Software License, Version 1.0. (See
  56           accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
  57           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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