boost/mpl/is_placeholder.hpp

   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: is_placeholder.hpp 49267 2008-10-11 06:19:02Z agurtovoy $
  14 // $Date: 2008-10-11 02:19:02 -0400 (Sat, 11 Oct 2008) $
  15 // $Revision: 49267 $
  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