1
2#ifndef BOOST_MPL_TAG_HPP_INCLUDED
3#define BOOST_MPL_TAG_HPP_INCLUDED
4
5// Copyright Aleksey Gurtovoy 2004
6//
7// Distributed under the Boost Software License, Version 1.0.
8// (See accompanying file LICENSE_1_0.txt or copy at
9// http://www.boost.org/LICENSE_1_0.txt)
10//
11// See http://www.boost.org/libs/mpl for documentation.
12
13// $Id$
14// $Date$
15// $Revision$
16
17#include <boost/mpl/eval_if.hpp>
18#include <boost/mpl/void.hpp>
19#include <boost/mpl/aux_/has_tag.hpp>
20#include <boost/mpl/aux_/config/eti.hpp>
21
22namespace boost { namespace mpl {
23
24namespace aux {
25template< typename T > struct tag_impl
26{
27 typedef typename T::tag type;
28};
29}
30
31template< typename T, typename Default = void_ > struct tag
32#if !defined(BOOST_MPL_CFG_MSVC_ETI_BUG)
33 : if_<
34 aux::has_tag<T>
35 , aux::tag_impl<T>
36 , Default
37 >::type
38{
39#else
40{
41 typedef typename eval_if<
42 aux::has_tag<T>
43 , aux::tag_impl<T>
44 , Default
45 >::type type;
46
47#endif
48};
49
50}}
51
52#endif // BOOST_MPL_TAG_HPP_INCLUDED
53