boost/mpl/tag.hpp

0001
0002 #ifndef BOOST_MPL_TAG_HPP_INCLUDED
0003 #define BOOST_MPL_TAG_HPP_INCLUDED
0004
0005 // Copyright Aleksey Gurtovoy 2004
0006 //
0007 // Distributed under the Boost Software License, Version 1.0.
0008 // (See accompanying file LICENSE_1_0.txt or copy at
0009 // http://www.boost.org/LICENSE_1_0.txt)
0010 //
0011 // See http://www.boost.org/libs/mpl for documentation.
0012
0013 // $Id$
0014 // $Date$
0015 // $Revision$
0016
0017 #include <boost/mpl/eval_if.hpp>
0018 #include <boost/mpl/void.hpp>
0019 #include <boost/mpl/aux_/has_tag.hpp>
0020 #include <boost/mpl/aux_/config/eti.hpp>
0021
0022 namespace boost { namespace mpl {
0023
0024 namespace aux {
0025 template< typename T > struct tag_impl
0026 {
0027     typedef typename T::tag type;
0028 };
0029 }
0030
0031 template< typename T, typename Default = void_ > struct tag
0032 #if !defined(BOOST_MPL_CFG_MSVC_ETI_BUG)
0033     : if_<
0034           aux::has_tag<T>
0035         , aux::tag_impl<T>
0036         , Default
0037         >::type
0038 {
0039 #else
0040 {
0041     typedef typename eval_if<
0042           aux::has_tag<T>
0043         , aux::tag_impl<T>
0044         , Default
0045         >::type type;
0046
0047 #endif
0048 };
0049
0050 }}
0051
0052 #endif // BOOST_MPL_TAG_HPP_INCLUDED