1 /////////////////////////////////////////////////////////////////////////////// 2 /// \file pop_front.hpp 3 /// Proto callables Fusion pop_front 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_POP_FRONT_HPP_EAN_11_27_2010 10 #define BOOST_PROTO_FUNCTIONAL_FUSION_POP_FRONT_HPP_EAN_11_27_2010 11 12 #include <boost/fusion/include/begin.hpp> 13 #include <boost/fusion/include/end.hpp> 14 #include <boost/fusion/include/next.hpp> 15 #include <boost/fusion/include/pop_front.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::pop_front() algorithm on its argument. 22 /// 23 /// A PolymorphicFunctionObject type that invokes the 24 /// \c fusion::pop_front() algorithm on its argument. This is 25 /// useful for defining a CallableTransform like \c pop_front(_) 26 /// which removes the first child from a Proto expression node. 27 /// Such a transform might be used as the first argument to the 28 /// \c proto::fold\<\> transform; that is, fold all but 29 /// the first child. 30 struct pop_front 31 { 32 BOOST_PROTO_CALLABLE() 33 34 template<typename Sig> 35 struct result; 36 37 template<typename This, typename Seq> 38 struct result<This(Seq)> 39 : result<This(Seq const &)> 40 {}; 41 42 template<typename This, typename Seq> 43 struct result<This(Seq &)> 44 : fusion::result_of::pop_front<Seq> 45 {}; 46 47 template<typename Seq> 48 typename fusion::result_of::pop_front<Seq>::type operator ()boost::proto::functional::pop_front49 operator ()(Seq &seq) const 50 { 51 // Work around a const-correctness issue in Fusion 52 typedef typename fusion::result_of::pop_front<Seq>::type result_type; 53 return result_type(fusion::next(fusion::begin(seq)), fusion::end(seq)); 54 } 55 56 template<typename Seq> 57 typename fusion::result_of::pop_front<Seq const>::type operator ()boost::proto::functional::pop_front58 operator ()(Seq const &seq) const 59 { 60 return fusion::pop_front(seq); 61 } 62 }; 63 }}} 64 65 #endif 66