boost/type_erasure/is_placeholder.hpp

0001 // Boost.TypeErasure library
0002 //
0003 // Copyright 2011 Steven Watanabe
0004 //
0005 // Distributed under the Boost Software License Version 1.0. (See
0006 // accompanying file LICENSE_1_0.txt or copy at
0007 // http://www.boost.org/LICENSE_1_0.txt)
0008 //
0009 // $Id$
0010
0011 #ifndef BOOST_TYPE_ERASURE_DETAIL_IS_PLACEHOLDER_HPP_INCLUDED
0012 #define BOOST_TYPE_ERASURE_DETAIL_IS_PLACEHOLDER_HPP_INCLUDED
0013
0014 #include <boost/mpl/bool.hpp>
0015
0016 namespace boost {
0017
0018 namespace type_erasure {
0019
0020 #ifdef BOOST_TYPE_ERASURE_DOXYGEN
0021
0022 /** A metafunction that indicates whether a type is a @ref placeholder. */
0023 template<class T>
0024 struct is_placeholder {};
0025
0026 #else
0027
0028 template<class T, class Enable = void>
0029 struct is_placeholder : ::boost::mpl::false_ {};
0030
0031 template<class T>
0032 struct is_placeholder<T, typename T::_boost_type_erasure_is_placeholder> :
0033     ::boost::mpl::true_ {};
0034
0035 #endif
0036
0037 }
0038 }
0039
0040 #endif