ceph/src/boost/libs/proto/include/boost/proto/transform/pass_through.hpp

   1 ///////////////////////////////////////////////////////////////////////////////
   2 /// \file pass_through.hpp
   3 ///
   4 /// Definition of the pass_through transform, which is the default transform
   5 /// of all of the expression generator metafunctions such as unary_plus<>, plus<>
   6 /// and nary_expr<>.
   7 //
   8 //  Copyright 2008 Eric Niebler. Distributed under the Boost
   9 //  Software License, Version 1.0. (See accompanying file
  10 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  11
  12 #ifndef BOOST_PROTO_TRANSFORM_PASS_THROUGH_HPP_EAN_12_26_2006
  13 #define BOOST_PROTO_TRANSFORM_PASS_THROUGH_HPP_EAN_12_26_2006
  14
  15 #include <boost/preprocessor/cat.hpp>
  16 #include <boost/preprocessor/repetition/enum.hpp>
  17 #include <boost/preprocessor/iteration/iterate.hpp>
  18 #include <boost/mpl/bool.hpp>
  19 #include <boost/mpl/if.hpp>
  20 #include <boost/type_traits/is_same.hpp>
  21 #include <boost/type_traits/remove_reference.hpp>
  22 #include <boost/proto/proto_fwd.hpp>
  23 #include <boost/proto/args.hpp>
  24 #include <boost/proto/transform/impl.hpp>
  25 #include <boost/proto/detail/ignore_unused.hpp>
  26
  27 #if defined(_MSC_VER)
  28 # pragma warning(push)
  29 # pragma warning(disable : 4714) // function 'xxx' marked as __forceinline not inlined
  30 #endif
  31
  32 namespace boost { namespace proto
  33 {
  34     namespace detail
  35     {
  36         template<
  37             typename Grammar
  38           , typename Domain
  39           , typename Expr
  40           , typename State
  41           , typename Data
  42           , long Arity = arity_of<Expr>::value
  43         >
  44         struct pass_through_impl
  45         {};
  46
  47         #include <boost/proto/transform/detail/pass_through_impl.hpp>
  48
  49         template<typename Grammar, typename Domain, typename Expr, typename State, typename Data>
  50         struct pass_through_impl<Grammar, Domain, Expr, State, Data, 0>
  51           : transform_impl<Expr, State, Data>
  52         {
  53             typedef Expr result_type;
  54
  55             /// \param e An expression
  56             /// \return \c e
  57             /// \throw nothrow
  58             BOOST_FORCEINLINE
  59             BOOST_PROTO_RETURN_TYPE_STRICT_LOOSE(result_type, typename pass_through_impl::expr_param)
  60             operator()(
  61                 typename pass_through_impl::expr_param e
  62               , typename pass_through_impl::state_param
  63               , typename pass_through_impl::data_param
  64             ) const
  65             {
  66                 return e;
  67             }
  68         };
  69
  70     } // namespace detail
  71
  72     /// \brief A PrimitiveTransform that transforms the child expressions
  73     /// of an expression node according to the corresponding children of
  74     /// a Grammar.
  75     ///
  76     /// Given a Grammar such as <tt>plus\<T0, T1\></tt>, an expression type
  77     /// that matches the grammar such as <tt>plus\<E0, E1\>::type</tt>, a
  78     /// state \c S and a data \c V, the result of applying the
  79     /// <tt>pass_through\<plus\<T0, T1\> \></tt> transform is:
  80     ///
  81     /// \code
  82     /// plus<
  83     ///     T0::result<T0(E0, S, V)>::type
  84     ///   , T1::result<T1(E1, S, V)>::type
  85     /// >::type
  86     /// \endcode
  87     ///
  88     /// The above demonstrates how child transforms and child expressions
  89     /// are applied pairwise, and how the results are reassembled into a new
  90     /// expression node with the same tag type as the original.
  91     ///
  92     /// The explicit use of <tt>pass_through\<\></tt> is not usually needed,
  93     /// since the expression generator metafunctions such as
  94     /// <tt>plus\<\></tt> have <tt>pass_through\<\></tt> as their default
  95     /// transform. So, for instance, these are equivalent:
  96     ///
  97     /// \code
  98     /// // Within a grammar definition, these are equivalent:
  99     /// when< plus<X, Y>, pass_through< plus<X, Y> > >
 100     /// when< plus<X, Y>, plus<X, Y> >
 101     /// when< plus<X, Y> > // because of when<class X, class Y=X>
 102     /// plus<X, Y>         // because plus<> is both a
 103     ///                    //   grammar and a transform
 104     /// \endcode
 105     ///
 106     /// For example, consider the following transform that promotes all
 107     /// \c float terminals in an expression to \c double.
 108     ///
 109     /// \code
 110     /// // This transform finds all float terminals in an expression and promotes
 111     /// // them to doubles.
 112     /// struct Promote
 113     ///  : or_<
 114     ///         when<terminal<float>, terminal<double>::type(_value) >
 115     ///         // terminal<>'s default transform is a no-op:
 116     ///       , terminal<_>
 117     ///         // nary_expr<> has a pass_through<> transform:
 118     ///       , nary_expr<_, vararg<Promote> >
 119     ///     >
 120     /// {};
 121     /// \endcode
 122     template<typename Grammar, typename Domain /* = deduce_domain*/>
 123     struct pass_through
 124       : transform<pass_through<Grammar, Domain> >
 125     {
 126         template<typename Expr, typename State, typename Data>
 127         struct impl
 128           : detail::pass_through_impl<Grammar, Domain, Expr, State, Data>
 129         {};
 130     };
 131
 132     /// INTERNAL ONLY
 133     ///
 134     template<typename Grammar, typename Domain>
 135     struct is_callable<pass_through<Grammar, Domain> >
 136       : mpl::true_
 137     {};
 138
 139 }} // namespace boost::proto
 140
 141 #if defined(_MSC_VER)
 142 # pragma warning(pop)
 143 #endif
 144
 145 #endif