category_of

Description

A metafunction that establishes the conceptual classification of a particular Sequence or Iterator (see Iterator Concepts and Sequence Concepts).

Synopsis

namespace traits
{
    template <typename T>
    struct category_of
    {
        typedef unspecified type;
    };
}

Parameters

Parameter	Requirement	Description
`T`	Any type	The type to query.

Expression Semantics

typedef traits::category_of<T>::type category;

Return type:

The return type is derived from one of:

namespace boost { namespace fusion
{
    struct incrementable_traversal_tag {};

    struct single_pass_traversal_tag
        : incrementable_traversal_tag {};

    struct forward_traversal_tag
        : single_pass_traversal_tag {};

    struct bidirectional_traversal_tag
        : forward_traversal_tag {};

    struct random_access_traversal_tag
        : bidirectional_traversal_tag {};
}}

And optionally from:

namespace boost { namespace fusion
{
    struct associative_tag {};
}}

Semantics: Establishes the conceptual classification of a particular Sequence or Iterator.

Header

#include <boost/fusion/support/category_of.hpp>
#include <boost/fusion/include/category_of.hpp>

Example

using boost::is_base_of;
typedef traits::category_of<list<> >::type list_category;
typedef traits::category_of<vector<> >::type vector_category;
BOOST_MPL_ASSERT(( is_base_of<forward_traversal_tag, list_category> ));
BOOST_MPL_ASSERT(( is_base_of<random_access_traversal_tag, vector_category> ));