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