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