54 lines
1.5 KiB
C++
54 lines
1.5 KiB
C++
// 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,
|
|
::boost::mpl::set0<>
|
|
>::type
|
|
>,
|
|
Metafunction,
|
|
::boost::mpl::identity<
|
|
::boost::type_erasure::deduced<Metafunction>
|
|
>
|
|
>::type type;
|
|
};
|
|
|
|
}
|
|
}
|
|
|
|
#endif
|