| /////////////////////////////////////////////////////////////////////////////// |
| /// \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 |