61 lines
2.6 KiB
HTML
61 lines
2.6 KiB
HTML
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<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>sequences.html</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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<h4> Sequences </h4>
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<div> A <i>sequence</i> (abbreviated to <i>seq</i>) is a group of adjacent
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parenthesized elements. For example, </div>
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<div class="code"> (<i>a</i>)(<i>b</i>)(<i>c</i>) </div>
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<div> ...is a <i>seq</i> of <i>3</i> elements--<i>a</i>, <i>b</i>, and <i>c</i>.
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</div>
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<div> <i>Sequences</i> are data structures that merge the properties of
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both <i>lists</i> and <i>tuples</i> with the exception that a <i>seq, </i>like
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a <i>tuple, </i>cannot be empty. Therefore, an "empty" <i>seq</i>
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is considered a special case scenario that must be handled separately in
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C++. </div>
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<div class="code">
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<pre>#define SEQ (x)(y)(z)
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#define REVERSE(s, state, elem) (elem) state
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// append to head ^
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BOOST_PP_SEQ_FOLD_LEFT(REVERSE, BOOST_PP_EMPTY, SEQ)()
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// #1 #2
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// 1) placeholder for "empty" seq
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// 2) remove placeholder
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#define SEQ_B (1)(2)(3)
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#define INC(s, state, elem) state (BOOST_PP_INC(elem))
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// append to tail ^
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BOOST_PP_SEQ_FOLD_RIGHT(INC, BOOST_PP_SEQ_NIL, SEQ)
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// ^
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// special placeholder that will be "eaten"
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// by appending to the tail
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</pre> </div>
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<div> <i>Sequences</i> are extremely efficient. Element access speed
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approaches random access--even with <i>seqs</i> of up to <i>256</i>
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elements. This is because element access (among other things) is
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implemented iteratively rather than recursively. Therefore, elements
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can be accessed at extremely high indices even on preprocessors with low
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maximum expansion depths. </div>
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<div> Elements of a <i>seq</i> can be extracted with <b>BOOST_PP_SEQ_ELEM</b>.
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</div>
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<h4> Primitives </h4>
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<ul>
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<li> <a href="../ref/seq_elem.html">BOOST_PP_SEQ_ELEM</a></li>
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</ul>
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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</i> </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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