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