boost/mpl/is_placeholder.hpp

0001
0002 #ifndef BOOST_MPL_IS_PLACEHOLDER_HPP_INCLUDED
0003 #define BOOST_MPL_IS_PLACEHOLDER_HPP_INCLUDED
0004
0005 // Copyright Aleksey Gurtovoy 2001-2004
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/arg_fwd.hpp>
0018 #include <boost/mpl/bool.hpp>
0019 #include <boost/mpl/aux_/yes_no.hpp>
0020 #include <boost/mpl/aux_/type_wrapper.hpp>
0021 #include <boost/mpl/aux_/nttp_decl.hpp>
0022 #include <boost/mpl/aux_/config/ctps.hpp>
0023 #include <boost/mpl/aux_/config/static_constant.hpp>
0024
0025 namespace boost { namespace mpl {
0026
0027 #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
0028
0029 template< typename T >
0030 struct is_placeholder
0031     : bool_<false>
0032 {
0033 };
0034
0035 template< BOOST_MPL_AUX_NTTP_DECL(int, N) >
0036 struct is_placeholder< arg<N> >
0037     : bool_<true>
0038 {
0039 };
0040
0041 #else
0042
0043 namespace aux {
0044
0045 aux::no_tag is_placeholder_helper(...);
0046
0047 template< BOOST_MPL_AUX_NTTP_DECL(int, N) >
0048 aux::yes_tag is_placeholder_helper(aux::type_wrapper< arg<N> >*);
0049
0050 } // namespace aux
0051
0052 template< typename T >
0053 struct is_placeholder
0054 {
0055     static aux::type_wrapper<T>* get();
0056     BOOST_STATIC_CONSTANT(bool, value =
0057           sizeof(aux::is_placeholder_helper(get())) == sizeof(aux::yes_tag)
0058         );
0059
0060     typedef bool_<value> type;
0061 };
0062
0063 #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
0064
0065 }}
0066
0067 #endif // BOOST_MPL_IS_PLACEHOLDER_HPP_INCLUDED