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1 | /////////////////////////////////////////////////////////////////////////////// |
2 | // droppable_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_DROPPABLE_ACCUMULATOR_HPP_EAN_13_12_2005 | |
9 | #define BOOST_ACCUMULATORS_FRAMEWORK_ACCUMULATORS_DROPPABLE_ACCUMULATOR_HPP_EAN_13_12_2005 | |
10 | ||
11 | #include <new> | |
12 | #include <boost/assert.hpp> | |
13 | #include <boost/mpl/apply.hpp> | |
14 | #include <boost/aligned_storage.hpp> | |
15 | #include <boost/accumulators/framework/depends_on.hpp> // for feature_of | |
16 | #include <boost/accumulators/framework/parameters/accumulator.hpp> // for accumulator | |
17 | ||
18 | namespace boost { namespace accumulators | |
19 | { | |
20 | ||
21 | template<typename Accumulator> | |
22 | struct droppable_accumulator; | |
23 | ||
24 | namespace detail | |
25 | { | |
26 | /////////////////////////////////////////////////////////////////////////////// | |
27 | // add_ref_visitor | |
28 | // a fusion function object for add_ref'ing accumulators | |
29 | template<typename Args> | |
30 | struct add_ref_visitor | |
31 | { | |
32 | explicit add_ref_visitor(Args const &args) | |
33 | : args_(args) | |
34 | { | |
35 | } | |
36 | ||
37 | template<typename Accumulator> | |
38 | void operator ()(Accumulator &acc) const | |
39 | { | |
40 | typedef typename Accumulator::feature_tag::dependencies dependencies; | |
41 | ||
42 | acc.add_ref(this->args_); | |
43 | ||
44 | // Also add_ref accumulators that this feature depends on | |
45 | this->args_[accumulator].template | |
46 | visit_if<detail::contains_feature_of_<dependencies> >( | |
47 | *this | |
48 | ); | |
49 | } | |
50 | ||
51 | private: | |
52 | add_ref_visitor &operator =(add_ref_visitor const &); | |
53 | Args const &args_; | |
54 | }; | |
55 | ||
56 | template<typename Args> | |
57 | add_ref_visitor<Args> make_add_ref_visitor(Args const &args) | |
58 | { | |
59 | return add_ref_visitor<Args>(args); | |
60 | } | |
61 | ||
62 | /////////////////////////////////////////////////////////////////////////////// | |
63 | // drop_visitor | |
64 | // a fusion function object for dropping accumulators | |
65 | template<typename Args> | |
66 | struct drop_visitor | |
67 | { | |
68 | explicit drop_visitor(Args const &args) | |
69 | : args_(args) | |
70 | { | |
71 | } | |
72 | ||
73 | template<typename Accumulator> | |
74 | void operator ()(Accumulator &acc) const | |
75 | { | |
76 | if(typename Accumulator::is_droppable()) | |
77 | { | |
78 | typedef typename Accumulator::feature_tag::dependencies dependencies; | |
79 | ||
80 | acc.drop(this->args_); | |
81 | // Also drop accumulators that this feature depends on | |
82 | this->args_[accumulator].template | |
83 | visit_if<detail::contains_feature_of_<dependencies> >( | |
84 | *this | |
85 | ); | |
86 | } | |
87 | } | |
88 | ||
89 | private: | |
90 | drop_visitor &operator =(drop_visitor const &); | |
91 | Args const &args_; | |
92 | }; | |
93 | ||
94 | template<typename Args> | |
95 | drop_visitor<Args> make_drop_visitor(Args const &args) | |
96 | { | |
97 | return drop_visitor<Args>(args); | |
98 | } | |
99 | } | |
100 | ||
101 | ////////////////////////////////////////////////////////////////////////// | |
102 | // droppable_accumulator_base | |
103 | template<typename Accumulator> | |
104 | struct droppable_accumulator_base | |
105 | : Accumulator | |
106 | { | |
107 | typedef droppable_accumulator_base base; | |
108 | typedef mpl::true_ is_droppable; | |
109 | typedef typename Accumulator::result_type result_type; | |
110 | ||
111 | template<typename Args> | |
112 | droppable_accumulator_base(Args const &args) | |
113 | : Accumulator(args) | |
114 | , ref_count_(0) | |
115 | { | |
116 | } | |
117 | ||
118 | droppable_accumulator_base(droppable_accumulator_base const &that) | |
119 | : Accumulator(*static_cast<Accumulator const *>(&that)) | |
120 | , ref_count_(that.ref_count_) | |
121 | { | |
122 | } | |
123 | ||
124 | template<typename Args> | |
125 | void operator ()(Args const &args) | |
126 | { | |
127 | if(!this->is_dropped()) | |
128 | { | |
129 | this->Accumulator::operator ()(args); | |
130 | } | |
131 | } | |
132 | ||
133 | template<typename Args> | |
134 | void add_ref(Args const &) | |
135 | { | |
136 | ++this->ref_count_; | |
137 | } | |
138 | ||
139 | template<typename Args> | |
140 | void drop(Args const &args) | |
141 | { | |
142 | BOOST_ASSERT(0 < this->ref_count_); | |
143 | if(1 == this->ref_count_) | |
144 | { | |
145 | static_cast<droppable_accumulator<Accumulator> *>(this)->on_drop(args); | |
146 | } | |
147 | --this->ref_count_; | |
148 | } | |
149 | ||
150 | bool is_dropped() const | |
151 | { | |
152 | return 0 == this->ref_count_; | |
153 | } | |
154 | ||
155 | private: | |
156 | int ref_count_; | |
157 | }; | |
158 | ||
159 | ////////////////////////////////////////////////////////////////////////// | |
160 | // droppable_accumulator | |
161 | // this can be specialized for any type that needs special handling | |
162 | template<typename Accumulator> | |
163 | struct droppable_accumulator | |
164 | : droppable_accumulator_base<Accumulator> | |
165 | { | |
166 | template<typename Args> | |
167 | droppable_accumulator(Args const &args) | |
168 | : droppable_accumulator::base(args) | |
169 | { | |
170 | } | |
171 | ||
172 | droppable_accumulator(droppable_accumulator const &that) | |
173 | : droppable_accumulator::base(*static_cast<typename droppable_accumulator::base const *>(&that)) | |
174 | { | |
175 | } | |
176 | }; | |
177 | ||
178 | ////////////////////////////////////////////////////////////////////////// | |
179 | // with_cached_result | |
180 | template<typename Accumulator> | |
181 | struct with_cached_result | |
182 | : Accumulator | |
183 | { | |
184 | typedef typename Accumulator::result_type result_type; | |
185 | ||
186 | template<typename Args> | |
187 | with_cached_result(Args const &args) | |
188 | : Accumulator(args) | |
189 | , cache() | |
190 | { | |
191 | } | |
192 | ||
193 | with_cached_result(with_cached_result const &that) | |
194 | : Accumulator(*static_cast<Accumulator const *>(&that)) | |
195 | , cache() | |
196 | { | |
197 | if(that.has_result()) | |
198 | { | |
199 | this->set(that.get()); | |
200 | } | |
201 | } | |
202 | ||
203 | ~with_cached_result() | |
204 | { | |
205 | // Since this is a base class of droppable_accumulator_base, | |
206 | // this destructor is called before any of droppable_accumulator_base's | |
207 | // members get cleaned up, including is_dropped, so the following | |
208 | // call to has_result() is valid. | |
209 | if(this->has_result()) | |
210 | { | |
211 | this->get().~result_type(); | |
212 | } | |
213 | } | |
214 | ||
215 | template<typename Args> | |
216 | void on_drop(Args const &args) | |
217 | { | |
218 | // cache the result at the point this calculation was dropped | |
219 | BOOST_ASSERT(!this->has_result()); | |
220 | this->set(this->Accumulator::result(args)); | |
221 | } | |
222 | ||
223 | template<typename Args> | |
224 | result_type result(Args const &args) const | |
225 | { | |
226 | return this->has_result() ? this->get() : this->Accumulator::result(args); | |
227 | } | |
228 | ||
229 | private: | |
230 | with_cached_result &operator =(with_cached_result const &); | |
231 | ||
232 | void set(result_type const &r) | |
233 | { | |
234 | ::new(this->cache.address()) result_type(r); | |
235 | } | |
236 | ||
237 | result_type const &get() const | |
238 | { | |
239 | return *static_cast<result_type const *>(this->cache.address()); | |
240 | } | |
241 | ||
242 | bool has_result() const | |
243 | { | |
244 | typedef with_cached_result<Accumulator> this_type; | |
245 | typedef droppable_accumulator_base<this_type> derived_type; | |
246 | return static_cast<derived_type const *>(this)->is_dropped(); | |
247 | } | |
248 | ||
249 | aligned_storage<sizeof(result_type)> cache; | |
250 | }; | |
251 | ||
252 | namespace tag | |
253 | { | |
254 | template<typename Feature> | |
255 | struct as_droppable | |
256 | { | |
257 | typedef droppable<Feature> type; | |
258 | }; | |
259 | ||
260 | template<typename Feature> | |
261 | struct as_droppable<droppable<Feature> > | |
262 | { | |
263 | typedef droppable<Feature> type; | |
264 | }; | |
265 | ||
266 | ////////////////////////////////////////////////////////////////////////// | |
267 | // droppable | |
268 | template<typename Feature> | |
269 | struct droppable | |
270 | : as_feature<Feature>::type | |
271 | { | |
272 | typedef typename as_feature<Feature>::type feature_type; | |
273 | typedef typename feature_type::dependencies tmp_dependencies_; | |
274 | ||
275 | typedef | |
276 | typename mpl::transform< | |
277 | typename feature_type::dependencies | |
278 | , as_droppable<mpl::_1> | |
279 | >::type | |
280 | dependencies; | |
281 | ||
282 | struct impl | |
283 | { | |
284 | template<typename Sample, typename Weight> | |
285 | struct apply | |
286 | { | |
287 | typedef | |
288 | droppable_accumulator< | |
289 | typename mpl::apply2<typename feature_type::impl, Sample, Weight>::type | |
290 | > | |
291 | type; | |
292 | }; | |
293 | }; | |
294 | }; | |
295 | } | |
296 | ||
297 | // make droppable<tag::feature(modifier)> work | |
298 | template<typename Feature> | |
299 | struct as_feature<tag::droppable<Feature> > | |
300 | { | |
301 | typedef tag::droppable<typename as_feature<Feature>::type> type; | |
302 | }; | |
303 | ||
304 | // make droppable<tag::mean> work with non-void weights (should become | |
305 | // droppable<tag::weighted_mean> | |
306 | template<typename Feature> | |
307 | struct as_weighted_feature<tag::droppable<Feature> > | |
308 | { | |
309 | typedef tag::droppable<typename as_weighted_feature<Feature>::type> type; | |
310 | }; | |
311 | ||
312 | // for the purposes of feature-based dependency resolution, | |
313 | // droppable<Foo> provides the same feature as Foo | |
314 | template<typename Feature> | |
315 | struct feature_of<tag::droppable<Feature> > | |
316 | : feature_of<Feature> | |
317 | { | |
318 | }; | |
319 | ||
320 | // Note: Usually, the extractor is pulled into the accumulators namespace with | |
321 | // a using directive, not the tag. But the droppable<> feature doesn't have an | |
322 | // extractor, so we can put the droppable tag in the accumulators namespace | |
323 | // without fear of a name conflict. | |
324 | using tag::droppable; | |
325 | ||
326 | }} // namespace boost::accumulators | |
327 | ||
328 | #endif |