iterator_category

Synopsis

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

#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 Iterators iter:

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

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
        >
{
};