ceph/src/boost/libs/mpl/doc/src/refmanual/iterator_category.rst

   1 .. Iterators/Iterator Metafunctions//iterator_category |60
   2
   3 iterator_category
   4 =================
   5
   6 Synopsis
   7 --------
   8
   9 .. parsed-literal::
  10
  11     template<
  12           typename Iterator
  13         >
  14     struct iterator_category
  15     {
  16         typedef typename Iterator::category type;
  17     };
  18
  19
  20
  21 Description
  22 -----------
  23
  24 Returns one of the following iterator category tags:
  25
  26 * ``forward_iterator_tag``
  27 * ``bidirectional_iterator_tag``
  28 * ``random_access_iterator_tag``
  29
  30
  31 Header
  32 ------
  33
  34 .. parsed-literal::
  35
  36     #include <boost/mpl/iterator_category.hpp>
  37     #include <boost/mpl/iterator_tags.hpp>
  38
  39
  40 Parameters
  41 ----------
  42
  43 +---------------+-----------------------+-------------------------------------------+
  44 | Parameter     | Requirement           | Description                               |
  45 +===============+=======================+===========================================+
  46 | ``Iterator``  | |Forward Iterator|    | The iterator to obtain a category for.    |
  47 +---------------+-----------------------+-------------------------------------------+
  48
  49
  50 Expression semantics
  51 --------------------
  52
  53 For any |Forward Iterator|\ s ``iter``:
  54
  55
  56 .. parsed-literal::
  57
  58     typedef iterator_category<iter>::type tag;
  59
  60 :Return type:
  61     |Integral Constant|.
  62
  63 :Semantics:
  64     ``tag`` is ``forward_iterator_tag`` if ``iter`` is a model of |Forward Iterator|,
  65     ``bidirectional_iterator_tag`` if ``iter`` is a model of |Bidirectional Iterator|,
  66     or ``random_access_iterator_tag`` if ``iter`` is a model of |Random Access Iterator|;
  67
  68 :Postcondition:
  69      ``forward_iterator_tag::value < bidirectional_iterator_tag::value``,
  70       ``bidirectional_iterator_tag::value < random_access_iterator_tag::value``.
  71
  72
  73 Complexity
  74 ----------
  75
  76 Amortized constant time.
  77
  78
  79 Example
  80 -------
  81
  82 .. parsed-literal::
  83
  84     template< typename Tag, typename Iterator >
  85     struct algorithm_impl
  86     {
  87         // *O(n)* implementation
  88     };
  89
  90     template< typename Iterator >
  91     struct algorithm_impl<random_access_iterator_tag,Iterator>
  92     {
  93         // *O(1)* implementation
  94     };
  95
  96     template< typename Iterator >
  97     struct algorithm
  98         : algorithm_impl<
  99               iterator_category<Iterator>::type
 100             , Iterator
 101             >
 102     {
 103     };
 104
 105
 106
 107 See also
 108 --------
 109
 110 |Iterators|, |begin| / |end|, |advance|, |distance|, |next|
 111
 112
 113 .. copyright:: Copyright ©  2001-2009 Aleksey Gurtovoy and David Abrahams
 114    Distributed under the Boost Software License, Version 1.0. (See accompanying
 115    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)