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
25namespace boost { namespace mpl {
26
27#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
28
29template< typename T >
30struct is_placeholder
31 : bool_<false>
32{
33};
34
35template< BOOST_MPL_AUX_NTTP_DECL(int, N) >
36struct is_placeholder< arg<N> >
37 : bool_<true>
38{
39};
40
41#else
42
43namespace aux {
44
45aux::no_tag is_placeholder_helper(...);
46
47template< BOOST_MPL_AUX_NTTP_DECL(int, N) >
48aux::yes_tag is_placeholder_helper(aux::type_wrapper< arg<N> >*);
49
50} // namespace aux
51
52template< typename T >
53struct 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

source code of boost/boost/mpl/is_placeholder.hpp