63e88f80
 Hu Chunming
提交三方库
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#ifndef BOOST_METAPARSE_V1_OPTIONAL_HPP
#define BOOST_METAPARSE_V1_OPTIONAL_HPP
// Copyright Abel Sinkovics (abel@sinkovics.hu) 2015.
// 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)
#include <boost/metaparse/v1/is_error.hpp>
#include <boost/metaparse/v1/accept.hpp>
#include <boost/mpl/if.hpp>
namespace boost
{
namespace metaparse
{
namespace v1
{
template <class P, class Default = void>
struct optional
{
typedef optional type;
template <class S, class Pos>
struct apply :
boost::mpl::if_<
is_error<typename P::template apply<S, Pos> >,
accept<Default, S, Pos>,
// is_error evaluates it anyway
typename P::template apply<S, Pos>::type
>
{};
};
}
}
}
#endif
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