// 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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