| 1 | // Boost.TypeErasure library |
|---|
| 2 | // |
|---|
| 3 | // Copyright 2011 Steven Watanabe |
|---|
| 4 | // |
|---|
| 5 | // Distributed under the Boost Software License Version 1.0. (See |
|---|
| 6 | // accompanying file LICENSE_1_0.txt or copy at |
|---|
| 7 | // http://www.boost.org/LICENSE_1_0.txt) |
|---|
| 8 | // |
|---|
| 9 | // $Id$ |
|---|
| 10 | |
|---|
| 11 | #ifndef BOOST_TYPE_ERASURE_DEDUCED_HPP_INCLUDED |
|---|
| 12 | #define BOOST_TYPE_ERASURE_DEDUCED_HPP_INCLUDED |
|---|
| 13 | |
|---|
| 14 | #include <boost/mpl/eval_if.hpp> |
|---|
| 15 | #include <boost/mpl/identity.hpp> |
|---|
| 16 | #include <boost/mpl/set.hpp> |
|---|
| 17 | #include <boost/mpl/empty.hpp> |
|---|
| 18 | #include <boost/type_erasure/detail/get_placeholders.hpp> |
|---|
| 19 | #include <boost/type_erasure/placeholder.hpp> |
|---|
| 20 | |
|---|
| 21 | namespace boost { |
|---|
| 22 | namespace type_erasure { |
|---|
| 23 | |
|---|
| 24 | /** |
|---|
| 25 | * A placeholder for an associated type. The type corresponding |
|---|
| 26 | * to this placeholder is deduced by substituting placeholders |
|---|
| 27 | * in the arguments of the metafunction and then evaluating it. |
|---|
| 28 | * |
|---|
| 29 | * When using @ref deduced in a template context, if it is possible for |
|---|
| 30 | * Metafunction to contain no placeholders at all, use the nested type, |
|---|
| 31 | * to automatically evaluate it early as needed. |
|---|
| 32 | */ |
|---|
| 33 | template<class Metafunction> |
|---|
| 34 | struct deduced : ::boost::type_erasure::placeholder |
|---|
| 35 | { |
|---|
| 36 | typedef typename ::boost::mpl::eval_if< |
|---|
| 37 | ::boost::mpl::empty< |
|---|
| 38 | typename ::boost::type_erasure::detail::get_placeholders< |
|---|
| 39 | Metafunction, |
|---|
| 40 | #ifndef BOOST_TYPE_ERASURE_USE_MP11 |
|---|
| 41 | ::boost::mpl::set0<> |
|---|
| 42 | #else |
|---|
| 43 | ::boost::mp11::mp_list<> |
|---|
| 44 | #endif |
|---|
| 45 | >::type |
|---|
| 46 | >, |
|---|
| 47 | Metafunction, |
|---|
| 48 | ::boost::mpl::identity< |
|---|
| 49 | ::boost::type_erasure::deduced<Metafunction> |
|---|
| 50 | > |
|---|
| 51 | >::type type; |
|---|
| 52 | }; |
|---|
| 53 | |
|---|
| 54 | } |
|---|
| 55 | } |
|---|
| 56 | |
|---|
| 57 | #endif |
|---|
| 58 | |
|---|
