| .. Iterators/Iterator Metafunctions//iterator_category |60 |
| |
| iterator_category |
| ================= |
| |
| Synopsis |
| -------- |
| |
| .. parsed-literal:: |
| |
| template< |
| typename Iterator |
| > |
| struct iterator_category |
| { |
| typedef typename Iterator::category type; |
| }; |
| |
| |
| |
| Description |
| ----------- |
| |
| Returns one of the following iterator category tags: |
| |
| * ``forward_iterator_tag`` |
| * ``bidirectional_iterator_tag`` |
| * ``random_access_iterator_tag`` |
| |
| |
| Header |
| ------ |
| |
| .. parsed-literal:: |
| |
| #include <boost/mpl/iterator_category.hpp> |
| #include <boost/mpl/iterator_tags.hpp> |
| |
| |
| Parameters |
| ---------- |
| |
| +---------------+-----------------------+-------------------------------------------+ |
| | Parameter | Requirement | Description | |
| +===============+=======================+===========================================+ |
| | ``Iterator`` | |Forward Iterator| | The iterator to obtain a category for. | |
| +---------------+-----------------------+-------------------------------------------+ |
| |
| |
| Expression semantics |
| -------------------- |
| |
| For any |Forward Iterator|\ s ``iter``: |
| |
| |
| .. parsed-literal:: |
| |
| typedef iterator_category<iter>::type tag; |
| |
| :Return type: |
| |Integral Constant|. |
| |
| :Semantics: |
| ``tag`` is ``forward_iterator_tag`` if ``iter`` is a model of |Forward Iterator|, |
| ``bidirectional_iterator_tag`` if ``iter`` is a model of |Bidirectional Iterator|, |
| or ``random_access_iterator_tag`` if ``iter`` is a model of |Random Access Iterator|; |
| |
| :Postcondition: |
| ``forward_iterator_tag::value < bidirectional_iterator_tag::value``, |
| ``bidirectional_iterator_tag::value < random_access_iterator_tag::value``. |
| |
| |
| Complexity |
| ---------- |
| |
| Amortized constant time. |
| |
| |
| Example |
| ------- |
| |
| .. parsed-literal:: |
| |
| template< typename Tag, typename Iterator > |
| struct algorithm_impl |
| { |
| // *O(n)* implementation |
| }; |
| |
| template< typename Iterator > |
| struct algorithm_impl<random_access_iterator_tag,Iterator> |
| { |
| // *O(1)* implementation |
| }; |
| |
| template< typename Iterator > |
| struct algorithm |
| : algorithm_impl< |
| iterator_category<Iterator>::type |
| , Iterator |
| > |
| { |
| }; |
| |
| |
| |
| See also |
| -------- |
| |
| |Iterators|, |begin| / |end|, |advance|, |distance|, |next| |
| |
| |
| .. copyright:: Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
