41 lines
970 B
C++
41 lines
970 B
C++
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#ifndef BOOST_METAPARSE_V1_OPTIONAL_HPP
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#define BOOST_METAPARSE_V1_OPTIONAL_HPP
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// Copyright Abel Sinkovics (abel@sinkovics.hu) 2015.
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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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#include <boost/metaparse/v1/is_error.hpp>
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#include <boost/metaparse/v1/accept.hpp>
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#include <boost/mpl/if.hpp>
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namespace boost
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{
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namespace metaparse
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{
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namespace v1
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{
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template <class P, class Default = void>
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struct optional
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{
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typedef optional type;
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template <class S, class Pos>
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struct apply :
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boost::mpl::if_<
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is_error<typename P::template apply<S, Pos> >,
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accept<Default, S, Pos>,
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// is_error evaluates it anyway
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typename P::template apply<S, Pos>::type
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>
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{};
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};
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}
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}
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}
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#endif
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