1.. Iterators/Iterator Metafunctions//iterator_category |60
2
3iterator_category
4=================
5
6Synopsis
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
21Description
22-----------
23
24Returns one of the following iterator category tags:
25
26* ``forward_iterator_tag``
27* ``bidirectional_iterator_tag``
28* ``random_access_iterator_tag``
29
30
31Header
32------
33
34.. parsed-literal::
35
36    #include <boost/mpl/iterator_category.hpp>
37    #include <boost/mpl/iterator_tags.hpp>
38
39
40Parameters
41----------
42
43+---------------+-----------------------+-------------------------------------------+
44| Parameter     | Requirement           | Description                               |
45+===============+=======================+===========================================+
46| ``Iterator``  | |Forward Iterator|    | The iterator to obtain a category for.    |
47+---------------+-----------------------+-------------------------------------------+
48
49
50Expression semantics
51--------------------
52
53For 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
73Complexity
74----------
75
76Amortized constant time.
77
78
79Example
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
107See 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)
116