boost/type_erasure/placeholder_of.hpp
// Boost.TypeErasure library
//
// Copyright 2011 Steven Watanabe
//
// Distributed under the Boost Software License Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
// $Id$
#ifndef BOOST_TYPE_ERASURE_PLACEHOLDER_OF_HPP_INCLUDED
#define BOOST_TYPE_ERASURE_PLACEHOLDER_OF_HPP_INCLUDED
namespace boost {
namespace type_erasure {
#ifndef BOOST_TYPE_ERASURE_DOXYGEN
template<class Concept, class T>
class any;
template<class Concept, class T>
class param;
#endif
/**
* A metafunction returning the (const/reference qualified) placeholder
* corresponding to an @ref any. It will also work for all bases
* of @ref any, so it can be applied to the @c Base
* parameter of @ref concept_interface.
*/
template<class T>
struct placeholder_of
{
#ifdef BOOST_TYPE_ERASURE_DOXYGEN
typedef detail::unspecified type;
#else
typedef typename ::boost::type_erasure::placeholder_of<
typename T::_boost_type_erasure_derived_type
>::type type;
#endif
};
/** INTERNAL ONLY */
template<class Concept, class T>
struct placeholder_of< ::boost::type_erasure::any<Concept, T> >
{
typedef T type;
};
/** INTERNAL ONLY */
template<class Concept, class T>
struct placeholder_of< ::boost::type_erasure::param<Concept, T> >
{
typedef T type;
};
#ifndef BOOST_NO_CXX11_TEMPLATE_ALIASES
template<class T>
using placeholder_of_t = typename ::boost::type_erasure::placeholder_of<T>::type;
#endif
}
}
#endif