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67 lines
1.9 KiB
67 lines
1.9 KiB
// Copyright David Abrahams, Daniel Wallin 2003. |
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// Distributed under the Boost Software License, Version 1.0. |
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// (See accompanying file LICENSE_1_0.txt or copy at |
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// http://www.boost.org/LICENSE_1_0.txt) |
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#ifndef BOOST_PARAMETER_OPTIONAL_HPP |
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#define BOOST_PARAMETER_OPTIONAL_HPP |
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#include <boost/parameter/aux_/use_default.hpp> |
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namespace boost { namespace parameter { |
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// This metafunction can be used to describe the treatment of particular |
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// named parameters for the purposes of overload elimination with SFINAE, |
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// by placing specializations in the parameters<...> list. In order for |
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// a treated function to participate in overload resolution: |
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// |
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// - The actual argument type matched by every keyword tag |
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// associated with a predicate must satisfy that predicate |
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// |
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// - If a keyword k is specified without an optional<...> or |
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// required<...> wrapper, it is treated as though |
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// optional<k> were specified. |
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template < |
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typename Tag |
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, typename Predicate = ::boost::parameter::aux::use_default |
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> |
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struct optional |
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{ |
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typedef Tag key_type; |
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typedef Predicate predicate; |
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}; |
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}} |
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#include <boost/parameter/config.hpp> |
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#if defined(BOOST_PARAMETER_CAN_USE_MP11) |
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#include <boost/mp11/integral.hpp> |
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#else |
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#include <boost/mpl/bool.hpp> |
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#endif |
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namespace boost { namespace parameter { namespace aux { |
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template <typename T> |
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struct is_optional |
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#if defined(BOOST_PARAMETER_CAN_USE_MP11) |
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: ::boost::mp11::mp_false |
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#else |
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: ::boost::mpl::false_ |
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#endif |
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{ |
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}; |
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template <typename Tag, typename Predicate> |
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struct is_optional< ::boost::parameter::optional<Tag,Predicate> > |
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#if defined(BOOST_PARAMETER_CAN_USE_MP11) |
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: ::boost::mp11::mp_true |
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#else |
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: ::boost::mpl::true_ |
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#endif |
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{ |
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}; |
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}}} // namespace boost::parameter::aux |
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#endif // include guard |
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