ceph/src/boost/boost/proto/functional/fusion/pop_front.hpp

   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
  49         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
  58         operator ()(Seq const &seq) const
  59         {
  60             return fusion::pop_front(seq);
  61         }
  62     };
  63 }}}
  64
  65 #endif