1 | /////////////////////////////////////////////////////////////////////////////// |
2 | // external_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_EXTERNAL_ACCUMULATOR_HPP_EAN_01_12_2005 |
9 | #define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_EXTERNAL_ACCUMULATOR_HPP_EAN_01_12_2005 |
10 | |
11 | #include <boost/mpl/placeholders.hpp> |
12 | #include <boost/parameter/keyword.hpp> |
13 | #include <boost/accumulators/framework/extractor.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/accumulators/reference_accumulator.hpp> |
17 | |
18 | namespace boost { namespace accumulators { namespace impl |
19 | { |
20 | |
21 | ////////////////////////////////////////////////////////////////////////// |
22 | // external_impl |
23 | /// INTERNAL ONLY |
24 | /// |
25 | template<typename Accumulator, typename Tag> |
26 | struct external_impl |
27 | : accumulator_base |
28 | { |
29 | typedef typename Accumulator::result_type result_type; |
30 | typedef typename detail::feature_tag<Accumulator>::type feature_tag; |
31 | |
32 | external_impl(dont_care) {} |
33 | |
34 | template<typename Args> |
35 | result_type result(Args const &args) const |
36 | { |
37 | return this->extract_(args, args[parameter::keyword<Tag>::get() | 0]); |
38 | } |
39 | |
40 | private: |
41 | |
42 | template<typename Args> |
43 | static result_type (Args const &args, int) |
44 | { |
45 | // No named parameter passed to the extractor. Maybe the external |
46 | // feature is held by reference<>. |
47 | extractor<feature_tag> ; |
48 | return extract(accumulators::reference_tag<Tag>(args)); |
49 | } |
50 | |
51 | template<typename Args, typename AccumulatorSet> |
52 | static result_type (Args const &, AccumulatorSet const &acc) |
53 | { |
54 | // OK, a named parameter for this external feature was passed to the |
55 | // extractor, so use that. |
56 | extractor<feature_tag> ; |
57 | return extract(acc); |
58 | } |
59 | }; |
60 | |
61 | } // namespace impl |
62 | |
63 | namespace tag |
64 | { |
65 | ////////////////////////////////////////////////////////////////////////// |
66 | // external |
67 | template<typename Feature, typename Tag, typename AccumulatorSet> |
68 | struct external |
69 | : depends_on<reference<AccumulatorSet, Tag> > |
70 | { |
71 | typedef |
72 | accumulators::impl::external_impl< |
73 | detail::to_accumulator<Feature, mpl::_1, mpl::_2> |
74 | , Tag |
75 | > |
76 | impl; |
77 | }; |
78 | |
79 | template<typename Feature, typename Tag> |
80 | struct external<Feature, Tag, void> |
81 | : depends_on<> |
82 | { |
83 | typedef |
84 | accumulators::impl::external_impl< |
85 | detail::to_accumulator<Feature, mpl::_1, mpl::_2> |
86 | , Tag |
87 | > |
88 | impl; |
89 | }; |
90 | } |
91 | |
92 | // for the purposes of feature-based dependency resolution, |
93 | // external_accumulator<Feature, Tag> provides the same feature as Feature |
94 | template<typename Feature, typename Tag, typename AccumulatorSet> |
95 | struct feature_of<tag::external<Feature, Tag, AccumulatorSet> > |
96 | : feature_of<Feature> |
97 | { |
98 | }; |
99 | |
100 | // Note: Usually, the extractor is pulled into the accumulators namespace with |
101 | // a using directive, not the tag. But the external<> feature doesn't have an |
102 | // extractor, so we can put the external tag in the accumulators namespace |
103 | // without fear of a name conflict. |
104 | using tag::external; |
105 | |
106 | }} // namespace boost::accumulators |
107 | |
108 | #endif |
109 | |