2004-11-29 06:33:06 +00:00
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.. Iterators/Iterator Metafunctions//distance |20
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2007-11-25 18:38:02 +00:00
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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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2004-11-29 06:33:06 +00:00
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distance
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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 First
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, typename Last
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>
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struct distance
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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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Returns the distance between ``First`` and ``Last`` iterators, that is, an
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|Integral Constant| ``n`` such that ``advance<First,n>::type`` is
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identical to ``Last``.
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Header
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------
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.. parsed-literal::
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#include <boost/mpl/distance.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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| ``First``, | |Forward Iterator| | Iterators to compute a |
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| ``Last`` | | distance between. |
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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 any |Forward Iterator|\ s ``first`` and ``last``:
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.. parsed-literal::
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typedef distance<first,last>::type n;
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:Return type:
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|Integral Constant|.
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:Precondition:
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[``first``, ``last``) is a valid range.
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:Semantics:
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Equivalent to
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.. parsed-literal::
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typedef iter_fold<
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iterator_range<first,last>
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, long_<0>
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, next<_1>
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>::type n;
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:Postcondition:
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``is_same< advance<first,n>::type, last >::value == true``.
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Complexity
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----------
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Amortized constant time if ``first`` and ``last`` are |Random Access Iterator|\ s,
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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>::type range;
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typedef begin<range>::type first;
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typedef end<range>::type last;
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BOOST_MPL_ASSERT_RELATION( (distance<first,last>::value), ==, 10);
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See also
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--------
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|Iterators|, |Tag Dispatched Metafunction|, |advance|, |next|, |prior|
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