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24 | </div> | |
25 | <div class="section boost_bimap_the_tutorial_discovering_the_bimap_framework"> | |
26 | <div class="titlepage"><div><div><h3 class="title"> | |
27 | <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework"></a><a class="link" href="discovering_the_bimap_framework.html" title="Discovering the bimap framework">Discovering | |
28 | the bimap framework</a> | |
29 | </h3></div></div></div> | |
30 | <div class="toc"><dl> | |
31 | <dt><span class="section"><a href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.interpreting_bidirectional_maps">Interpreting | |
32 | bidirectional maps</a></span></dt> | |
33 | <dt><span class="section"><a href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.standard_mapping_framework">Standard | |
34 | mapping framework</a></span></dt> | |
35 | <dt><span class="section"><a href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.bimap_mapping_framework">Bimap | |
36 | mapping framework</a></span></dt> | |
37 | </dl></div> | |
38 | <div class="section boost_bimap_the_tutorial_discovering_the_bimap_framework_interpreting_bidirectional_maps"> | |
39 | <div class="titlepage"><div><div><h4 class="title"> | |
40 | <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework.interpreting_bidirectional_maps"></a><a class="link" href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.interpreting_bidirectional_maps" title="Interpreting bidirectional maps">Interpreting | |
41 | bidirectional maps</a> | |
42 | </h4></div></div></div> | |
43 | <p> | |
44 | One way to interpret bidirectional maps is as a function between two collections | |
45 | of data, lets call them the left and the right collection. An element in | |
46 | this bimap is a relation between an element from the left collection and | |
47 | an element from the right collection. The types of both collections defines | |
48 | the bimap behaviour. We can view the stored data from the left side, as | |
49 | a mapping between keys from the left collection and data from the right | |
50 | one, or from the right side, as a mapping between keys from the right collection | |
51 | and data from the left collection. | |
52 | </p> | |
53 | </div> | |
54 | <div class="section boost_bimap_the_tutorial_discovering_the_bimap_framework_standard_mapping_framework"> | |
55 | <div class="titlepage"><div><div><h4 class="title"> | |
56 | <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework.standard_mapping_framework"></a><a class="link" href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.standard_mapping_framework" title="Standard mapping framework">Standard | |
57 | mapping framework</a> | |
58 | </h4></div></div></div> | |
59 | <p> | |
60 | Relationships between data in the STL are represented by maps. A standard | |
61 | map is a directed relation of keys from a left collection and data from | |
62 | a right unconstrained collection. The following diagram shows the relationship | |
63 | represented and the user's viewpoint. | |
64 | </p> | |
65 | <p> | |
66 | <span class="inlinemediaobject"><img src="../../images/bimap/standard.mapping.framework.png" alt="standard.mapping.framework"></span> | |
67 | </p> | |
68 | <p> | |
69 | The left collection type depends on the selected map type. For example | |
70 | if the the map type is <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">multimap</span></code> | |
71 | the collection type of X is a <code class="computeroutput"><span class="identifier">multiset_of</span></code>. | |
72 | The following table shows the equivalent types for the std associative | |
73 | containers. | |
74 | </p> | |
75 | <div class="table"> | |
76 | <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework.standard_mapping_framework.t0"></a><p class="title"><b>Table 1.1. std associative containers</b></p> | |
77 | <div class="table-contents"><table class="table" summary="std associative containers"> | |
78 | <colgroup> | |
79 | <col> | |
80 | <col> | |
81 | <col> | |
82 | </colgroup> | |
83 | <thead><tr> | |
84 | <th> | |
85 | <p> | |
86 | container | |
87 | </p> | |
88 | </th> | |
89 | <th> | |
90 | <p> | |
91 | left collection type | |
92 | </p> | |
93 | </th> | |
94 | <th> | |
95 | <p> | |
96 | right collection type | |
97 | </p> | |
98 | </th> | |
99 | </tr></thead> | |
100 | <tbody> | |
101 | <tr> | |
102 | <td> | |
103 | <p> | |
104 | <code class="computeroutput"><span class="identifier">map</span></code> | |
105 | </p> | |
106 | </td> | |
107 | <td> | |
108 | <p> | |
109 | <code class="computeroutput"><span class="identifier">set_of</span></code> | |
110 | </p> | |
111 | </td> | |
112 | <td> | |
113 | <p> | |
114 | no constraints | |
115 | </p> | |
116 | </td> | |
117 | </tr> | |
118 | <tr> | |
119 | <td> | |
120 | <p> | |
121 | <code class="computeroutput"><span class="identifier">multimap</span></code> | |
122 | </p> | |
123 | </td> | |
124 | <td> | |
125 | <p> | |
126 | <code class="computeroutput"><span class="identifier">multiset_of</span></code> | |
127 | </p> | |
128 | </td> | |
129 | <td> | |
130 | <p> | |
131 | no constraints | |
132 | </p> | |
133 | </td> | |
134 | </tr> | |
135 | <tr> | |
136 | <td> | |
137 | <p> | |
138 | <code class="computeroutput"><span class="identifier">unordered_map</span></code> | |
139 | </p> | |
140 | </td> | |
141 | <td> | |
142 | <p> | |
143 | <code class="computeroutput"><span class="identifier">unordered_set_of</span></code> | |
144 | </p> | |
145 | </td> | |
146 | <td> | |
147 | <p> | |
148 | no constraints | |
149 | </p> | |
150 | </td> | |
151 | </tr> | |
152 | <tr> | |
153 | <td> | |
154 | <p> | |
155 | <code class="computeroutput"><span class="identifier">unordered_multimap</span></code> | |
156 | </p> | |
157 | </td> | |
158 | <td> | |
159 | <p> | |
160 | <code class="computeroutput"><span class="identifier">unordered_multiset_of</span></code> | |
161 | </p> | |
162 | </td> | |
163 | <td> | |
164 | <p> | |
165 | no constraints | |
166 | </p> | |
167 | </td> | |
168 | </tr> | |
169 | </tbody> | |
170 | </table></div> | |
171 | </div> | |
172 | <br class="table-break"> | |
173 | </div> | |
174 | <div class="section boost_bimap_the_tutorial_discovering_the_bimap_framework_bimap_mapping_framework"> | |
175 | <div class="titlepage"><div><div><h4 class="title"> | |
176 | <a name="boost_bimap.the_tutorial.discovering_the_bimap_framework.bimap_mapping_framework"></a><a class="link" href="discovering_the_bimap_framework.html#boost_bimap.the_tutorial.discovering_the_bimap_framework.bimap_mapping_framework" title="Bimap mapping framework">Bimap | |
177 | mapping framework</a> | |
178 | </h4></div></div></div> | |
179 | <p> | |
180 | Boost.Bimap design is based on the STL, and extends the framework in a | |
181 | natural way. The following diagram represents the new situation. | |
182 | </p> | |
183 | <p> | |
184 | <span class="inlinemediaobject"><img src="../../images/bimap/extended.mapping.framework.png" alt="extended.mapping.framework"></span> | |
185 | </p> | |
186 | <p> | |
187 | Notice that now the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">maps</span></code> | |
188 | are a particular case of a Boost.Bimap container, where you can view only | |
189 | one side of the relationship and can control the constraints of only one | |
190 | of the collections. Boost.Bimap allows the user to view the relationship | |
191 | from three viewpoints. You can view it from one side, obtaining a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code> compatible container, or you can | |
192 | work directly with the whole relation. | |
193 | </p> | |
194 | <p> | |
195 | The next diagram shows the layout of the relation and pairs of a bimap. | |
196 | It is the one from the <span class="emphasis"><em>one minute tutorial</em></span> | |
197 | </p> | |
198 | <p> | |
199 | <span class="inlinemediaobject"><img src="../../images/bimap/relation.and.pair.png" alt="relation.and.pair"></span> | |
200 | </p> | |
201 | <p> | |
202 | Bimap pairs are signature-compatible with standard pairs but are different | |
203 | from them. As you will see in other sections they can be tagged with user | |
204 | defined names and additional information can be attached to them. You can | |
205 | convert from <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pairs</span></code> to bimap pairs directly but the | |
206 | reverse conversion is not provided. This mean that you can insert elements | |
207 | in a bimap using algorithms like <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">copy</span></code> | |
208 | from containers <code class="computeroutput"><span class="identifier">like</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code>, | |
209 | or use <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span></code> to add new elements. However | |
210 | it is best to use <code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">left</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span> <span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_value_type</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="identifier">s</span><span class="special">)</span> <span class="special">)</span></code> instead | |
211 | of <code class="computeroutput"><span class="identifier">bm</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="identifier">s</span><span class="special">)</span> <span class="special">)</span></code> to avoid | |
212 | an extra call to the copy constructor of each type. | |
213 | </p> | |
214 | <p> | |
215 | The following code snippet shows the relation between a bimap and standard | |
216 | maps. | |
217 | </p> | |
218 | <div class="note"><table border="0" summary="Note"> | |
219 | <tr> | |
220 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
221 | <th align="left">Note</th> | |
222 | </tr> | |
223 | <tr><td align="left" valign="top"> | |
224 | <p> | |
225 | You have to use references to views, and not directly views object. | |
226 | Views cannot be constructed as separate objects from the container they | |
227 | belong to, so the following: | |
228 | </p> | |
229 | <pre class="programlisting"><span class="comment">// Wrong: we forgot the & after bm_type::left_type</span> | |
230 | <span class="identifier">bm_type</span><span class="special">::</span><span class="identifier">left_map</span> <span class="identifier">lm</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifier">left</span><span class="special">;</span> | |
231 | </pre> | |
232 | <p> | |
233 | does not compile, since it is trying to construct the view object <code class="computeroutput"><span class="identifier">lm</span></code>. This is a common source of errors | |
234 | in user code. | |
235 | </p> | |
236 | </td></tr> | |
237 | </table></div> | |
238 | <p> | |
239 | <a href="../../../../example/standard_map_comparison.cpp" target="_top">Go to source code</a> | |
240 | </p> | |
241 | <p> | |
242 | </p> | |
243 | <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">Map</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CompatibleKey</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CompatibleData</span> <span class="special">></span> | |
244 | <span class="keyword">void</span> <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">Map</span> <span class="special">&</span> <span class="identifier">m</span><span class="special">,</span> | |
245 | <span class="keyword">const</span> <span class="identifier">CompatibleKey</span> <span class="special">&</span> <span class="identifier">key</span><span class="special">,</span> | |
246 | <span class="keyword">const</span> <span class="identifier">CompatibleData</span> <span class="special">&</span> <span class="identifier">data</span> <span class="special">)</span> | |
247 | <span class="special">{</span> | |
248 | <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">Map</span><span class="special">::</span><span class="identifier">value_type</span> <span class="identifier">value_type</span><span class="special">;</span> | |
249 | <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">Map</span><span class="special">::</span><span class="identifier">const_iterator</span> <span class="identifier">const_iterator</span><span class="special">;</span> | |
250 | ||
251 | <span class="identifier">m</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span> <span class="identifier">value_type</span><span class="special">(</span><span class="identifier">key</span><span class="special">,</span><span class="identifier">data</span><span class="special">)</span> <span class="special">);</span> | |
252 | <span class="identifier">const_iterator</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">find</span><span class="special">(</span><span class="identifier">key</span><span class="special">);</span> | |
253 | <span class="keyword">if</span><span class="special">(</span> <span class="identifier">iter</span> <span class="special">!=</span> <span class="identifier">m</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">)</span> | |
254 | <span class="special">{</span> | |
255 | <span class="identifier">assert</span><span class="special">(</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">first</span> <span class="special">==</span> <span class="identifier">key</span> <span class="special">);</span> | |
256 | <span class="identifier">assert</span><span class="special">(</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">second</span> <span class="special">==</span> <span class="identifier">data</span> <span class="special">);</span> | |
257 | ||
258 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">first</span> <span class="special"><<</span> <span class="string">" --> "</span> <span class="special"><<</span> <span class="identifier">iter</span><span class="special">-></span><span class="identifier">second</span><span class="special">;</span> | |
259 | <span class="special">}</span> | |
260 | <span class="identifier">m</span><span class="special">.</span><span class="identifier">erase</span><span class="special">(</span><span class="identifier">key</span><span class="special">);</span> | |
261 | <span class="special">}</span> | |
262 | ||
263 | <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> | |
264 | <span class="special">{</span> | |
265 | <span class="keyword">typedef</span> <span class="identifier">bimap</span><span class="special"><</span> <span class="identifier">set_of</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>,</span> <span class="identifier">set_of</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="special">></span> <span class="identifier">bimap_type</span><span class="special">;</span> | |
266 | <span class="identifier">bimap_type</span> <span class="identifier">bm</span><span class="special">;</span> | |
267 | ||
268 | <span class="comment">// Standard map</span> | |
269 | <span class="special">{</span> | |
270 | <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">,</span> <span class="keyword">int</span> <span class="special">></span> <span class="identifier">map_type</span><span class="special">;</span> | |
271 | <span class="identifier">map_type</span> <span class="identifier">m</span><span class="special">;</span> | |
272 | ||
273 | <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">m</span><span class="special">,</span> <span class="string">"one"</span><span class="special">,</span> <span class="number">1</span> <span class="special">);</span> | |
274 | <span class="special">}</span> | |
275 | ||
276 | <span class="comment">// Left map view</span> | |
277 | <span class="special">{</span> | |
278 | <span class="keyword">typedef</span> <span class="identifier">bimap_type</span><span class="special">::</span><span class="identifier">left_map</span> <span class="identifier">map_type</span><span class="special">;</span> | |
279 | <span class="identifier">map_type</span> <span class="special">&</span> <span class="identifier">m</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifier">left</span><span class="special">;</span> | |
280 | ||
281 | <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">m</span><span class="special">,</span> <span class="string">"one"</span><span class="special">,</span> <span class="number">1</span> <span class="special">);</span> | |
282 | <span class="special">}</span> | |
283 | ||
284 | <span class="comment">// Reverse standard map</span> | |
285 | <span class="special">{</span> | |
286 | <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">></span> <span class="identifier">reverse_map_type</span><span class="special">;</span> | |
287 | <span class="identifier">reverse_map_type</span> <span class="identifier">rm</span><span class="special">;</span> | |
288 | ||
289 | <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">rm</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="string">"one"</span> <span class="special">);</span> | |
290 | <span class="special">}</span> | |
291 | ||
292 | <span class="comment">// Right map view</span> | |
293 | <span class="special">{</span> | |
294 | <span class="keyword">typedef</span> <span class="identifier">bimap_type</span><span class="special">::</span><span class="identifier">right_map</span> <span class="identifier">reverse_map_type</span><span class="special">;</span> | |
295 | <span class="identifier">reverse_map_type</span> <span class="special">&</span> <span class="identifier">rm</span> <span class="special">=</span> <span class="identifier">bm</span><span class="special">.</span><span class="identifier">right</span><span class="special">;</span> | |
296 | ||
297 | <span class="identifier">use_it</span><span class="special">(</span> <span class="identifier">rm</span><span class="special">,</span> <span class="number">1</span><span class="special">,</span> <span class="string">"one"</span> <span class="special">);</span> | |
298 | <span class="special">}</span> | |
299 | ||
300 | <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> | |
301 | <span class="special">}</span> | |
302 | </pre> | |
303 | <p> | |
304 | </p> | |
305 | </div> | |
306 | </div> | |
307 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
308 | <td align="left"></td> | |
309 | <td align="right"><div class="copyright-footer">Copyright © 2006-2012 Matias Capeletto<p> | |
310 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
311 | file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) | |
312 | </p> | |
313 | </div></td> | |
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