1 2 #ifndef BOOST_MPL_IS_PLACEHOLDER_HPP_INCLUDED 3 #define BOOST_MPL_IS_PLACEHOLDER_HPP_INCLUDED 4 5 // Copyright Aleksey Gurtovoy 2001-2004 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/arg_fwd.hpp> 18 #include <boost/mpl/bool.hpp> 19 #include <boost/mpl/aux_/yes_no.hpp> 20 #include <boost/mpl/aux_/type_wrapper.hpp> 21 #include <boost/mpl/aux_/nttp_decl.hpp> 22 #include <boost/mpl/aux_/config/ctps.hpp> 23 #include <boost/mpl/aux_/config/static_constant.hpp> 24 25 namespace boost { namespace mpl { 26 27 #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) 28 29 template< typename T > 30 struct is_placeholder 31 : bool_<false> 32 { 33 }; 34 35 template< BOOST_MPL_AUX_NTTP_DECL(int, N) > 36 struct is_placeholder< arg<N> > 37 : bool_<true> 38 { 39 }; 40 41 #else 42 43 namespace aux { 44 45 aux::no_tag is_placeholder_helper(...); 46 47 template< BOOST_MPL_AUX_NTTP_DECL(int, N) > 48 aux::yes_tag is_placeholder_helper(aux::type_wrapper< arg<N> >*); 49 50 } // namespace aux 51 52 template< typename T > 53 struct is_placeholder 54 { 55 static aux::type_wrapper<T>* get(); 56 BOOST_STATIC_CONSTANT(bool, value = 57 sizeof(aux::is_placeholder_helper(get())) == sizeof(aux::yes_tag) 58 ); 59 60 typedef bool_<value> type; 61 }; 62 63 #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION 64 65 }} 66 67 #endif // BOOST_MPL_IS_PLACEHOLDER_HPP_INCLUDED 68