Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: /// \file pass_through.hpp
Chris@16: ///
Chris@16: /// Definition of the pass_through transform, which is the default transform
Chris@16: /// of all of the expression generator metafunctions such as unary_plus<>, plus<>
Chris@16: /// and nary_expr<>.
Chris@16: //
Chris@16: //  Copyright 2008 Eric Niebler. Distributed under the Boost
Chris@16: //  Software License, Version 1.0. (See accompanying file
Chris@16: //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef BOOST_PROTO_TRANSFORM_PASS_THROUGH_HPP_EAN_12_26_2006
Chris@16: #define BOOST_PROTO_TRANSFORM_PASS_THROUGH_HPP_EAN_12_26_2006
Chris@16: 
Chris@16: #include <boost/preprocessor/cat.hpp>
Chris@16: #include <boost/preprocessor/repetition/enum.hpp>
Chris@16: #include <boost/preprocessor/iteration/iterate.hpp>
Chris@16: #include <boost/mpl/bool.hpp>
Chris@16: #include <boost/mpl/if.hpp>
Chris@16: #include <boost/type_traits/is_same.hpp>
Chris@16: #include <boost/type_traits/remove_reference.hpp>
Chris@16: #include <boost/proto/proto_fwd.hpp>
Chris@16: #include <boost/proto/args.hpp>
Chris@16: #include <boost/proto/transform/impl.hpp>
Chris@16: #include <boost/proto/detail/ignore_unused.hpp>
Chris@16: 
Chris@101: #if defined(_MSC_VER)
Chris@16: # pragma warning(push)
Chris@16: # pragma warning(disable : 4714) // function 'xxx' marked as __forceinline not inlined
Chris@16: #endif
Chris@16: 
Chris@16: namespace boost { namespace proto
Chris@16: {
Chris@16:     namespace detail
Chris@16:     {
Chris@16:         template<
Chris@16:             typename Grammar
Chris@16:           , typename Domain
Chris@16:           , typename Expr
Chris@16:           , typename State
Chris@16:           , typename Data
Chris@16:           , long Arity = arity_of<Expr>::value
Chris@16:         >
Chris@16:         struct pass_through_impl
Chris@16:         {};
Chris@16: 
Chris@16:         #include <boost/proto/transform/detail/pass_through_impl.hpp>
Chris@16: 
Chris@16:         template<typename Grammar, typename Domain, typename Expr, typename State, typename Data>
Chris@16:         struct pass_through_impl<Grammar, Domain, Expr, State, Data, 0>
Chris@16:           : transform_impl<Expr, State, Data>
Chris@16:         {
Chris@16:             typedef Expr result_type;
Chris@16: 
Chris@16:             /// \param e An expression
Chris@16:             /// \return \c e
Chris@16:             /// \throw nothrow
Chris@16:             BOOST_FORCEINLINE
Chris@16:             BOOST_PROTO_RETURN_TYPE_STRICT_LOOSE(result_type, typename pass_through_impl::expr_param)
Chris@16:             operator()(
Chris@16:                 typename pass_through_impl::expr_param e
Chris@16:               , typename pass_through_impl::state_param
Chris@16:               , typename pass_through_impl::data_param
Chris@16:             ) const
Chris@16:             {
Chris@16:                 return e;
Chris@16:             }
Chris@16:         };
Chris@16: 
Chris@16:     } // namespace detail
Chris@16: 
Chris@16:     /// \brief A PrimitiveTransform that transforms the child expressions
Chris@16:     /// of an expression node according to the corresponding children of
Chris@16:     /// a Grammar.
Chris@16:     ///
Chris@16:     /// Given a Grammar such as <tt>plus\<T0, T1\></tt>, an expression type
Chris@16:     /// that matches the grammar such as <tt>plus\<E0, E1\>::type</tt>, a
Chris@16:     /// state \c S and a data \c V, the result of applying the
Chris@16:     /// <tt>pass_through\<plus\<T0, T1\> \></tt> transform is:
Chris@16:     ///
Chris@16:     /// \code
Chris@16:     /// plus<
Chris@16:     ///     T0::result<T0(E0, S, V)>::type
Chris@16:     ///   , T1::result<T1(E1, S, V)>::type
Chris@16:     /// >::type
Chris@16:     /// \endcode
Chris@16:     ///
Chris@16:     /// The above demonstrates how child transforms and child expressions
Chris@16:     /// are applied pairwise, and how the results are reassembled into a new
Chris@16:     /// expression node with the same tag type as the original.
Chris@16:     ///
Chris@16:     /// The explicit use of <tt>pass_through\<\></tt> is not usually needed,
Chris@16:     /// since the expression generator metafunctions such as
Chris@16:     /// <tt>plus\<\></tt> have <tt>pass_through\<\></tt> as their default
Chris@16:     /// transform. So, for instance, these are equivalent:
Chris@16:     ///
Chris@16:     /// \code
Chris@16:     /// // Within a grammar definition, these are equivalent:
Chris@16:     /// when< plus<X, Y>, pass_through< plus<X, Y> > >
Chris@16:     /// when< plus<X, Y>, plus<X, Y> >
Chris@16:     /// when< plus<X, Y> > // because of when<class X, class Y=X>
Chris@16:     /// plus<X, Y>         // because plus<> is both a
Chris@16:     ///                    //   grammar and a transform
Chris@16:     /// \endcode
Chris@16:     ///
Chris@16:     /// For example, consider the following transform that promotes all
Chris@16:     /// \c float terminals in an expression to \c double.
Chris@16:     ///
Chris@16:     /// \code
Chris@16:     /// // This transform finds all float terminals in an expression and promotes
Chris@16:     /// // them to doubles.
Chris@16:     /// struct Promote
Chris@16:     ///  : or_<
Chris@16:     ///         when<terminal<float>, terminal<double>::type(_value) >
Chris@16:     ///         // terminal<>'s default transform is a no-op:
Chris@16:     ///       , terminal<_>
Chris@16:     ///         // nary_expr<> has a pass_through<> transform:
Chris@16:     ///       , nary_expr<_, vararg<Promote> >
Chris@16:     ///     >
Chris@16:     /// {};
Chris@16:     /// \endcode
Chris@16:     template<typename Grammar, typename Domain /* = deduce_domain*/>
Chris@16:     struct pass_through
Chris@16:       : transform<pass_through<Grammar, Domain> >
Chris@16:     {
Chris@16:         template<typename Expr, typename State, typename Data>
Chris@16:         struct impl
Chris@16:           : detail::pass_through_impl<Grammar, Domain, Expr, State, Data>
Chris@16:         {};
Chris@16:     };
Chris@16: 
Chris@16:     /// INTERNAL ONLY
Chris@16:     ///
Chris@16:     template<typename Grammar, typename Domain>
Chris@16:     struct is_callable<pass_through<Grammar, Domain> >
Chris@16:       : mpl::true_
Chris@16:     {};
Chris@16: 
Chris@16: }} // namespace boost::proto
Chris@16: 
Chris@101: #if defined(_MSC_VER)
Chris@16: # pragma warning(pop)
Chris@16: #endif
Chris@16: 
Chris@16: #endif