boost/bimap/relation/member_at.hpp

// Boost.Bimap
//
// Copyright (c) 2006-2007 Matias Capeletto
//
// 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)
/// \file relation/member_at.hpp
/// \brief Defines the tags for the member_at::side idiom
#ifndef BOOST_BIMAP_RELATION_MEMBER_AT_HPP
#define BOOST_BIMAP_RELATION_MEMBER_AT_HPP
#if defined(_MSC_VER)
#pragma once
#endif
#include <boost/config.hpp>
namespace boost {
namespace bimaps {
namespace relation {
/// \brief member_at::side idiom to access relation values and types using metaprogramming. 
/**
This tags are used to specify which member you want to acces when using a metafunction over
a symmetrical type. The idea is to be able to write code like:
\code
result_of::get<member_at::left,relation>::type data = get<member_at::left>(rel);
\endcode
The relation class supports this idiom even when the elements are tagged. This is useful
because a user can decide to start tagging in any moment of the development.
See also member_with_tag, is_tag_of_member_at_left, is_tag_of_member_at_right, get
value_type_of, pair_by, pair_type_by.
\ingroup relation_group
                                                                                        **/
namespace member_at {
    /// \brief Member at left tag
    /**
    See also member_at, rigth.
                                            **/
    struct left  {};
    /// \brief Member at right tag
    /**
    See also member_at, left.
                                            **/
    struct right {};
    /// \brief Member info tag
    /**
    See also member_at, left, right.
                                            **/
    struct info  {};
}
} // namespace relation
} // namespace bimaps
} // namespace boost
#endif // BOOST_BIMAP_RELATION_MEMBER_AT_HPP