| // Copyright David Abrahams, Daniel Wallin 2003. |
| // 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) |
| |
| #ifndef BOOST_PARAMETER_OPTIONAL_HPP |
| #define BOOST_PARAMETER_OPTIONAL_HPP |
| |
| #include <boost/parameter/aux_/use_default.hpp> |
| |
| namespace boost { namespace parameter { |
| |
| // This metafunction can be used to describe the treatment of particular |
| // named parameters for the purposes of overload elimination with SFINAE, |
| // by placing specializations in the parameters<...> list. In order for |
| // a treated function to participate in overload resolution: |
| // |
| // - The actual argument type matched by every keyword tag |
| // associated with a predicate must satisfy that predicate |
| // |
| // - If a keyword k is specified without an optional<...> or |
| // required<...> wrapper, it is treated as though |
| // optional<k> were specified. |
| template < |
| typename Tag |
| , typename Predicate = ::boost::parameter::aux::use_default |
| > |
| struct optional |
| { |
| typedef Tag key_type; |
| typedef Predicate predicate; |
| }; |
| }} |
| |
| #include <boost/parameter/config.hpp> |
| |
| #if defined(BOOST_PARAMETER_CAN_USE_MP11) |
| #include <boost/mp11/integral.hpp> |
| #else |
| #include <boost/mpl/bool.hpp> |
| #endif |
| |
| namespace boost { namespace parameter { namespace aux { |
| |
| template <typename T> |
| struct is_optional |
| #if defined(BOOST_PARAMETER_CAN_USE_MP11) |
| : ::boost::mp11::mp_false |
| #else |
| : ::boost::mpl::false_ |
| #endif |
| { |
| }; |
| |
| template <typename Tag, typename Predicate> |
| struct is_optional< ::boost::parameter::optional<Tag,Predicate> > |
| #if defined(BOOST_PARAMETER_CAN_USE_MP11) |
| : ::boost::mp11::mp_true |
| #else |
| : ::boost::mpl::true_ |
| #endif |
| { |
| }; |
| }}} // namespace boost::parameter::aux |
| |
| #endif // include guard |
| |