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
32namespace 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
146