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135 lines
2.9 KiB
ReStructuredText
135 lines
2.9 KiB
ReStructuredText
.. Iterators/Iterator Metafunctions//advance |10
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.. Copyright Aleksey Gurtovoy, David Abrahams 2007.
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.. Distributed under the Boost
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.. Software License, Version 1.0. (See accompanying
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.. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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advance
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=======
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Synopsis
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--------
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.. parsed-literal::
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template<
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typename Iterator
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, typename N
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>
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struct advance
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{
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typedef |unspecified| type;
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};
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Description
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-----------
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Moves ``Iterator`` by the distance ``N``. For |bidirectional| and
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|random access| iterators, the distance may be negative.
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Header
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------
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.. parsed-literal::
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#include <boost/mpl/advance.hpp>
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Parameters
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----------
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+---------------+---------------------------+-----------------------------------+
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| Parameter | Requirement | Description |
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+===============+===========================+===================================+
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| ``Iterator`` | |Forward Iterator| | An iterator to advance. |
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+---------------+---------------------------+-----------------------------------+
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| ``N`` | |Integral Constant| | A distance. |
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+---------------+---------------------------+-----------------------------------+
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Model Of
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--------
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|Tag Dispatched Metafunction|
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Expression semantics
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--------------------
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For a |Forward Iterator| ``iter`` and arbitrary |Integral Constant| ``n``:
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.. parsed-literal::
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typedef advance<iter,n>::type j;
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:Return type:
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|Forward Iterator|.
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:Precondition:
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If ``Iterator`` is a |Forward Iterator|, ``n::value`` must be nonnegative.
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:Semantics:
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Equivalent to:
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.. parsed-literal::
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typedef iter i0;
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typedef next<i0>::type i1;
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|...|
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typedef next<i\ *n-1*\ >::type j;
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if ``n::value > 0``, and
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.. parsed-literal::
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typedef iter i0;
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typedef prior<i0>::type i1;
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|...|
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typedef prior<i\ *n-1*\ >::type j;
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otherwise.
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:Postcondition:
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``j`` is dereferenceable or past-the-end;
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``distance<iter,j>::value == n::value`` if ``n::value > 0``, and
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``distance<j,iter>::value == n::value`` otherwise.
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Complexity
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----------
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Amortized constant time if ``iter`` is a model of
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|Random Access Iterator|, otherwise linear time.
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Example
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-------
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.. parsed-literal::
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typedef range_c<int,0,10> numbers;
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typedef begin<numbers>::type first;
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typedef end<numbers>::type last;
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typedef advance<first,int_<10> >::type i1;
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typedef advance<last,int_<-10> >::type i2;
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BOOST_MPL_ASSERT(( boost::is_same<i1,last> ));
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BOOST_MPL_ASSERT(( boost::is_same<i2,first> ));
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See also
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--------
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|Iterators|, |Tag Dispatched Metafunction|, |distance|, |next|
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.. |bidirectional| replace:: `bidirectional`_
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.. _bidirectional: `Bidirectional Iterator`_
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.. |random access| replace:: `random access`_
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.. _random access: `Random Access Iterator`_
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