1 /////////////////////////////////////////////////////////////////////////////// 2 /// \file at.hpp 3 /// Proto callables Fusion at 4 // 5 // Copyright 2010 Eric Niebler. Distributed under the Boost 6 // Software License, Version 1.0. (See accompanying file 7 // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 8 9 #ifndef BOOST_PROTO_FUNCTIONAL_FUSION_AT_HPP_EAN_11_27_2010 10 #define BOOST_PROTO_FUNCTIONAL_FUSION_AT_HPP_EAN_11_27_2010 11 12 #include <boost/type_traits/add_const.hpp> 13 #include <boost/type_traits/remove_const.hpp> 14 #include <boost/type_traits/remove_reference.hpp> 15 #include <boost/fusion/include/at.hpp> 16 #include <boost/proto/proto_fwd.hpp> 17 18 namespace boost { namespace proto { namespace functional 19 { 20 /// \brief A PolymorphicFunctionObject type that invokes the 21 /// \c fusion::at() accessor on its argument. 22 /// 23 /// A PolymorphicFunctionObject type that invokes the 24 /// \c fusion::at() accessor on its argument. 25 struct at 26 { 27 BOOST_PROTO_CALLABLE() 28 29 template<typename Sig> 30 struct result; 31 32 template<typename This, typename Seq, typename N> 33 struct result<This(Seq, N)> 34 : fusion::result_of::at< 35 typename boost::remove_reference<Seq>::type 36 , typename boost::remove_const<typename boost::remove_reference<N>::type>::type 37 > 38 {}; 39 40 template<typename Seq, typename N> 41 typename fusion::result_of::at<Seq, N>::type operator ()boost::proto::functional::at42 operator ()(Seq &seq, N const & BOOST_PROTO_DISABLE_IF_IS_CONST(Seq)) const 43 { 44 return fusion::at<N>(seq); 45 } 46 47 template<typename Seq, typename N> 48 typename fusion::result_of::at<Seq const, N>::type operator ()boost::proto::functional::at49 operator ()(Seq const &seq, N const &) const 50 { 51 return fusion::at<N>(seq); 52 } 53 }; 54 }}} 55 56 #endif 57