v1/cpp11/first_of.hpp

0001 #ifndef BOOST_METAPARSE_V1_CPP11_FIRST_OF_HPP
0002 #define BOOST_METAPARSE_V1_CPP11_FIRST_OF_HPP
0003
0004 // Copyright Abel Sinkovics (abel@sinkovics.hu)  2017.
0005 // Distributed under the Boost Software License, Version 1.0.
0006 //    (See accompanying file LICENSE_1_0.txt or copy at
0007 //          http://www.boost.org/LICENSE_1_0.txt)
0008
0009 #include <boost/metaparse/v1/cpp11/impl/nth_of_c.hpp>
0010
0011 #include <boost/metaparse/v1/fail.hpp>
0012 #include <boost/metaparse/v1/error/index_out_of_range.hpp>
0013
0014 namespace boost
0015 {
0016   namespace metaparse
0017   {
0018     namespace v1
0019     {
0020       template <class... Ps>
0021       struct first_of
0022       {
0023         typedef first_of type;
0024
0025         template <class S, class Pos>
0026         struct apply : impl::nth_of_c<0, S, Pos, Ps...> {};
0027       };
0028
0029       template <>
0030       struct first_of<> : fail<error::index_out_of_range<0, -1, 0>> {};
0031     }
0032   }
0033 }
0034
0035 #endif
0036