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 |
329 | |