1 | /////////////////////////////////////////////////////////////////////////////// |
2 | // reference_accumulator.hpp |
3 | // |
4 | // Copyright 2005 Eric Niebler. Distributed under the Boost |
5 | // Software License, Version 1.0. (See accompanying file |
6 | // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
7 | |
8 | #ifndef BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006 |
9 | #define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_REFERENCE_ACCUMULATOR_HPP_EAN_03_23_2006 |
10 | |
11 | #include <boost/ref.hpp> |
12 | #include <boost/mpl/always.hpp> |
13 | #include <boost/parameter/keyword.hpp> |
14 | #include <boost/accumulators/framework/depends_on.hpp> // for feature_tag |
15 | #include <boost/accumulators/framework/accumulator_base.hpp> |
16 | #include <boost/accumulators/framework/extractor.hpp> |
17 | |
18 | namespace boost { namespace accumulators |
19 | { |
20 | |
21 | namespace impl |
22 | { |
23 | ////////////////////////////////////////////////////////////////////////// |
24 | // reference_accumulator_impl |
25 | // |
26 | template<typename Referent, typename Tag> |
27 | struct reference_accumulator_impl |
28 | : accumulator_base |
29 | { |
30 | typedef Referent &result_type; |
31 | |
32 | template<typename Args> |
33 | reference_accumulator_impl(Args const &args) |
34 | : ref(args[parameter::keyword<Tag>::instance]) |
35 | { |
36 | } |
37 | |
38 | result_type result(dont_care) const |
39 | { |
40 | return this->ref; |
41 | } |
42 | |
43 | private: |
44 | reference_wrapper<Referent> ref; |
45 | }; |
46 | } // namespace impl |
47 | |
48 | namespace tag |
49 | { |
50 | ////////////////////////////////////////////////////////////////////////// |
51 | // reference_tag |
52 | template<typename Tag> |
53 | struct reference_tag |
54 | { |
55 | }; |
56 | |
57 | ////////////////////////////////////////////////////////////////////////// |
58 | // reference |
59 | template<typename Referent, typename Tag> |
60 | struct reference |
61 | : depends_on<> |
62 | { |
63 | /// INTERNAL ONLY |
64 | /// |
65 | typedef mpl::always<accumulators::impl::reference_accumulator_impl<Referent, Tag> > impl; |
66 | }; |
67 | } |
68 | |
69 | namespace extract |
70 | { |
71 | BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, , (typename)(typename)) |
72 | BOOST_ACCUMULATORS_DEFINE_EXTRACTOR(tag, , (typename)) |
73 | } |
74 | |
75 | using extract::reference; |
76 | using extract::reference_tag; |
77 | |
78 | // Map all reference<V,T> features to reference_tag<T> so |
79 | // that references can be extracted using reference_tag<T> |
80 | // without specifying the referent type. |
81 | template<typename ValueType, typename Tag> |
82 | struct feature_of<tag::reference<ValueType, Tag> > |
83 | : feature_of<tag::reference_tag<Tag> > |
84 | { |
85 | }; |
86 | |
87 | }} // namespace boost::accumulators |
88 | |
89 | #endif |
90 | |