boost/type_erasure/deduced.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_DEDUCED_HPP_INCLUDED
#define BOOST_TYPE_ERASURE_DEDUCED_HPP_INCLUDED
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/mpl/set.hpp>
#include <boost/mpl/empty.hpp>
#include <boost/type_erasure/detail/get_placeholders.hpp>
#include <boost/type_erasure/placeholder.hpp>
namespace boost {
namespace type_erasure {
/**
* A placeholder for an associated type. The type corresponding
* to this placeholder is deduced by substituting placeholders
* in the arguments of the metafunction and then evaluating it.
*
* When using @ref deduced in a template context, if it is possible for
* Metafunction to contain no placeholders at all, use the nested type,
* to automatically evaluate it early as needed.
*/
template<class Metafunction>
struct deduced : ::boost::type_erasure::placeholder
{
typedef typename ::boost::mpl::eval_if<
::boost::mpl::empty<
typename ::boost::type_erasure::detail::get_placeholders<
Metafunction,
#ifndef BOOST_TYPE_ERASURE_USE_MP11
::boost::mpl::set0<>
#else
::boost::mp11::mp_list<>
#endif
>::type
>,
Metafunction,
::boost::mpl::identity<
::boost::type_erasure::deduced<Metafunction>
>
>::type type;
};
}
}
#endif