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| 6 | <title>Boost.MultiIndex Documentation - Tutorial - Techniques</title> | |
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| 14 | <body> | |
| 15 | <h1><img src="../../../../boost.png" alt="boost.png (6897 bytes)" align= | |
| 16 | "middle" width="277" height="86">Boost.MultiIndex Tutorial: Techniques</h1> | |
| 17 | ||
| 18 | <div class="prev_link"><a href="debug.html"><img src="../prev.gif" alt="debugging support" border="0"><br> | |
| 19 | Debugging support | |
| 20 | </a></div> | |
| 21 | <div class="up_link"><a href="index.html"><img src="../up.gif" alt="Boost.MultiIndex tutorial" border="0"><br> | |
| 22 | Boost.MultiIndex tutorial | |
| 23 | </a></div> | |
| 24 | <div class="next_link"><a href="../reference/index.html"><img src="../next.gif" alt="Boost.MultiIndex reference" border="0"><br> | |
| 25 | Boost.MultiIndex reference | |
| 26 | </a></div><br clear="all" style="clear: all;"> | |
| 27 | ||
| 28 | <hr> | |
| 29 | ||
| 30 | <h2>Contents</h2> | |
| 31 | ||
| 32 | <ul> | |
| 33 | <li><a href="#emulate_std_containers">Emulating standard containers with | |
| 34 | <code>multi_index_container</code></a> | |
| 35 | <ul> | |
| 36 | <li><a href="#emulate_assoc_containers">Emulation of associative | |
| 37 | containers</a></li> | |
| 38 | <li><a href="#emulate_std_list">Emulation of <code>std::list</code></a></li> | |
| 39 | </ul> | |
| 40 | </li> | |
| 41 | <li><a href="#metaprogrammming">Metaprogramming and <code>multi_index_container</code></a> | |
| 42 | <ul> | |
| 43 | <li><a href="#mpl_analysis">MPL analysis</a></li> | |
| 44 | <li><a href="#mpl_synthesis">MPL synthesis</a></li> | |
| 45 | </ul> | |
| 46 | </li> | |
| 47 | </ul> | |
| 48 | ||
| 49 | <h2><a name="emulate_std_containers">Emulating standard containers with | |
| 50 | <code>multi_index_container</code></a></h2> | |
| 51 | ||
| 52 | <h3><a name="emulate_assoc_containers">Emulation of associative | |
| 53 | containers</a></h3> | |
| 54 | ||
| 55 | <p> | |
| 56 | Academic movitations aside, there is a practical interest in emulating standard | |
| 57 | associative containers by means of <code>multi_index_container</code>, namely to take | |
| 58 | advantage of extended functionalities provided by <code>multi_index_container</code> for | |
| 59 | lookup, range querying and updating. | |
| 60 | </p> | |
| 61 | ||
| 62 | <p> | |
| 63 | In order to emulate a <code>std::set</code> one can follow the substitution | |
| 64 | rule: | |
| 65 | </p> | |
| 66 | ||
| 67 | <blockquote><pre> | |
| 68 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>set</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>Compare</span><span class=special>,</span><span class=identifier>Allocator</span><span class=special>></span> <span class=special>-></span> | |
| 69 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 70 | <span class=identifier>Key</span><span class=special>,</span> | |
| 71 | <span class=identifier>indexed_by</span><span class=special><</span><span class=identifier>ordered_unique</span><span class=special><</span><span class=identifier>identity</span><span class=special><</span><span class=identifier>Key</span><span class=special>>,</span><span class=identifier>Compare</span><span class=special>></span> <span class=special>>,</span> | |
| 72 | <span class=identifier>Allocator</span> | |
| 73 | <span class=special>></span> | |
| 74 | </pre></blockquote> | |
| 75 | ||
| 76 | <p> | |
| 77 | In the default case where <code>Compare=std::less<Key></code> and | |
| 78 | <code>Allocator=std::allocator<Key></code>, the substitution rule is | |
| 79 | simplified as | |
| 80 | </p> | |
| 81 | ||
| 82 | <blockquote><pre> | |
| 83 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>set</span><span class=special><</span><span class=identifier>Key</span><span class=special>></span> <span class=special>-></span> <span class=identifier>multi_index_container</span><span class=special><</span><span class=identifier>Key</span><span class=special>></span> | |
| 84 | </pre></blockquote> | |
| 85 | ||
| 86 | <p> | |
| 87 | The substitution of <code>multi_index_container</code> for <code>std::set</code> keeps | |
| 88 | the whole set of functionality provided by <code>std::set</code>, so in | |
| 89 | principle it is a drop-in replacement needing no further adjustments. | |
| 90 | </p> | |
| 91 | ||
| 92 | <p> | |
| 93 | <code>std::multiset</code> can be emulated in a similar manner, according to the | |
| 94 | following rule: | |
| 95 | </p> | |
| 96 | ||
| 97 | <blockquote><pre> | |
| 98 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>multiset</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>Compare</span><span class=special>,</span><span class=identifier>Allocator</span><span class=special>></span> <span class=special>-></span> | |
| 99 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 100 | <span class=identifier>Key</span><span class=special>,</span> | |
| 101 | <span class=identifier>indexed_by</span><span class=special><</span><span class=identifier>ordered_non_unique</span><span class=special><</span><span class=identifier>identity</span><span class=special><</span><span class=identifier>Key</span><span class=special>>,</span><span class=identifier>Compare</span><span class=special>></span> <span class=special>>,</span> | |
| 102 | <span class=identifier>Allocator</span> | |
| 103 | <span class=special>></span> | |
| 104 | </pre></blockquote> | |
| 105 | ||
| 106 | <p> | |
| 107 | When default values are taken into consideration, the rule takes the form | |
| 108 | </p> | |
| 109 | ||
| 110 | <blockquote><pre> | |
| 111 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>multiset</span><span class=special><</span><span class=identifier>Key</span><span class=special>></span> <span class=special>-></span> | |
| 112 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 113 | <span class=identifier>Key</span><span class=special>,</span> | |
| 114 | <span class=identifier>indexed_by</span><span class=special><</span><span class=identifier>ordered_non_unique</span><span class=special><</span><span class=identifier>identity</span><span class=special><</span><span class=identifier>Key</span><span class=special>></span> <span class=special>></span> <span class=special>></span> | |
| 115 | <span class=special>></span> | |
| 116 | </pre></blockquote> | |
| 117 | ||
| 118 | <p> | |
| 119 | The emulation of <code>std::multiset</code>s with <code>multi_index_container</code> | |
| 120 | results in a slight difference with respect to the interface offered: the member | |
| 121 | function <code>insert(const value_type&)</code> does not return an | |
| 122 | <code>iterator</code> as in <code>std::multiset</code>s, but rather a | |
| 123 | <code>std::pair<iterator,bool></code> in the spirit of <code>std::set</code>s. | |
| 124 | In this particular case, however, the <code>bool</code> member of the returned | |
| 125 | pair is always <code>true</code>. | |
| 126 | </p> | |
| 127 | ||
| 128 | <p> | |
| 129 | The case of <code>std::map</code>s and <code>std::multimap</code>s does not lend | |
| 130 | itself to such a direct emulation by means of <code>multi_index_container</code>. The main | |
| 131 | problem lies in the fact that elements of a <code>multi_index_container</code> are treated | |
| 132 | as constant, while the <code>std::map</code> and <code>std::multimap</code> handle | |
| 133 | objects of type <code>std::pair<const Key,T></code>, thus allowing for free | |
| 134 | modification of the value part. To overcome this difficulty we need to create an ad | |
| 135 | hoc pair class: | |
| 136 | </p> | |
| 137 | ||
| 138 | <blockquote><pre> | |
| 139 | <span class=keyword>template</span> <span class=special><</span><span class=keyword>typename</span> <span class=identifier>T1</span><span class=special>,</span><span class=keyword>typename</span> <span class=identifier>T2</span><span class=special>></span> | |
| 140 | <span class=keyword>struct</span> <span class=identifier>mutable_pair</span> | |
| 141 | <span class=special>{</span> | |
| 142 | <span class=keyword>typedef</span> <span class=identifier>T1</span> <span class=identifier>first_type</span><span class=special>;</span> | |
| 143 | <span class=keyword>typedef</span> <span class=identifier>T2</span> <span class=identifier>second_type</span><span class=special>;</span> | |
| 144 | ||
| 145 | <span class=identifier>mutable_pair</span><span class=special>():</span><span class=identifier>first</span><span class=special>(</span><span class=identifier>T1</span><span class=special>()),</span><span class=identifier>second</span><span class=special>(</span><span class=identifier>T2</span><span class=special>()){}</span> | |
| 146 | <span class=identifier>mutable_pair</span><span class=special>(</span><span class=keyword>const</span> <span class=identifier>T1</span><span class=special>&</span> <span class=identifier>f</span><span class=special>,</span><span class=keyword>const</span> <span class=identifier>T2</span><span class=special>&</span> <span class=identifier>s</span><span class=special>):</span><span class=identifier>first</span><span class=special>(</span><span class=identifier>f</span><span class=special>),</span><span class=identifier>second</span><span class=special>(</span><span class=identifier>s</span><span class=special>){}</span> | |
| 147 | <span class=identifier>mutable_pair</span><span class=special>(</span><span class=keyword>const</span> <span class=identifier>std</span><span class=special>::</span><span class=identifier>pair</span><span class=special><</span><span class=identifier>T1</span><span class=special>,</span><span class=identifier>T2</span><span class=special>>&</span> <span class=identifier>p</span><span class=special>):</span><span class=identifier>first</span><span class=special>(</span><span class=identifier>p</span><span class=special>.</span><span class=identifier>first</span><span class=special>),</span><span class=identifier>second</span><span class=special>(</span><span class=identifier>p</span><span class=special>.</span><span class=identifier>second</span><span class=special>){}</span> | |
| 148 | ||
| 149 | <span class=identifier>T1</span> <span class=identifier>first</span><span class=special>;</span> | |
| 150 | <span class=keyword>mutable</span> <span class=identifier>T2</span> <span class=identifier>second</span><span class=special>;</span> | |
| 151 | <span class=special>};</span> | |
| 152 | </pre></blockquote> | |
| 153 | ||
| 154 | <p> | |
| 155 | and so the substitution rules are: | |
| 156 | </p> | |
| 157 | ||
| 158 | <blockquote><pre> | |
| 159 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>map</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>T</span><span class=special>,</span><span class=identifier>Compare</span><span class=special>,</span><span class=identifier>Allocator</span><span class=special>></span> <span class=special>-></span> | |
| 160 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 161 | <span class=identifier>Element</span><span class=special>,</span> | |
| 162 | <span class=identifier>indexed_by</span><span class=special><</span> | |
| 163 | <span class=identifier>ordered_unique</span><span class=special><</span><span class=identifier>member</span><span class=special><</span><span class=identifier>Element</span><span class=special>,</span><span class=identifier>Key</span><span class=special>,&</span><span class=identifier>Element</span><span class=special>::</span><span class=identifier>first</span><span class=special>>,</span><span class=identifier>Compare</span><span class=special>></span> | |
| 164 | <span class=special>>,</span> | |
| 165 | <span class=keyword>typename</span> <span class=identifier>Allocator</span><span class=special>::</span><span class=keyword>template</span> <span class=identifier>rebind</span><span class=special><</span><span class=identifier>Element</span><span class=special>>::</span><span class=identifier>other</span> | |
| 166 | <span class=special>></span> | |
| 167 | ||
| 168 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>multimap</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>T</span><span class=special>,</span><span class=identifier>Compare</span><span class=special>,</span><span class=identifier>Allocator</span><span class=special>></span> <span class=special>-></span> | |
| 169 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 170 | <span class=identifier>Element</span><span class=special>,</span> | |
| 171 | <span class=identifier>indexed_by</span><span class=special><</span> | |
| 172 | <span class=identifier>ordered_non_unique</span><span class=special><</span><span class=identifier>member</span><span class=special><</span><span class=identifier>Element</span><span class=special>,</span><span class=identifier>Key</span><span class=special>,&</span><span class=identifier>Element</span><span class=special>::</span><span class=identifier>first</span><span class=special>>,</span><span class=identifier>Compare</span><span class=special>></span> | |
| 173 | <span class=special>>,</span> | |
| 174 | <span class=keyword>typename</span> <span class=identifier>Allocator</span><span class=special>::</span><span class=keyword>template</span> <span class=identifier>rebind</span><span class=special><</span><span class=identifier>Element</span><span class=special>>::</span><span class=identifier>other</span> | |
| 175 | <span class=special>></span> | |
| 176 | ||
| 177 | (<span class=identifier>with</span> <span class=identifier>Element</span><span class=special>=</span><span class=identifier>mutable_pair</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>T</span><span class=special>></span>) | |
| 178 | </pre></blockquote> | |
| 179 | ||
| 180 | <p> | |
| 181 | If default values are considered, the rules take the form: | |
| 182 | </p> | |
| 183 | ||
| 184 | <blockquote><pre> | |
| 185 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>map</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>T</span><span class=special>></span> <span class=special>-></span> | |
| 186 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 187 | <span class=identifier>Element</span><span class=special>, | |
| 188 | </span><span class=identifier>indexed_by</span><span class=special><</span><span class=identifier>ordered_unique</span><span class=special><</span><span class=identifier>member</span><span class=special><</span><span class=identifier>Element</span><span class=special>,</span><span class=identifier>Key</span><span class=special>,&</span><span class=identifier>Element</span><span class=special>::</span><span class=identifier>first</span><span class=special>></span> <span class=special>></span> <span class=special>></span> | |
| 189 | <span class=special>></span> | |
| 190 | ||
| 191 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>multimap</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>T</span><span class=special>></span> <span class=special>-></span> | |
| 192 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 193 | <span class=identifier>Element</span><span class=special>, | |
| 194 | </span><span class=identifier>indexed_by</span><span class=special><</span><span class=identifier>ordered_non_unique</span><span class=special><</span><span class=identifier>member</span><span class=special><</span><span class=identifier>Element</span><span class=special>,</span><span class=identifier>Key</span><span class=special>,&</span><span class=identifier>Element</span><span class=special>::</span><span class=identifier>first</span><span class=special>></span> <span class=special>></span> <span class=special>></span> | |
| 195 | <span class=special>></span> | |
| 196 | ||
| 197 | (<span class=identifier>with</span> <span class=identifier>Element</span><span class=special>=</span><span class=identifier>mutable_pair</span><span class=special><</span><span class=identifier>Key</span><span class=special>,</span><span class=identifier>T</span><span class=special>></span>) | |
| 198 | </pre></blockquote> | |
| 199 | ||
| 200 | <p> | |
| 201 | Unlike as with standard sets, the interface of these <code>multi_index_container</code>-emulated | |
| 202 | maps does not exactly conform to that of <code>std::map</code>s and | |
| 203 | <code>std::multimap</code>s. The most obvious difference is the lack of | |
| 204 | <code>operator []</code>, either in read or write mode; this, however, can be | |
| 205 | emulated with appropriate use of <code>find</code> and <code>insert</code>. | |
| 206 | </p> | |
| 207 | ||
| 208 | <p> | |
| 209 | These emulations of standard associative containers with <code>multi_index_container</code> | |
| 210 | are comparable to the original constructs in terms of space and time efficiency. | |
| 211 | See the <a href="../performance.html">performance section</a> for further details. | |
| 212 | </p> | |
| 213 | ||
| 214 | <h3><a name="emulate_std_list">Emulation of <code>std::list</code></a></h3> | |
| 215 | ||
| 216 | <p> | |
| 217 | Unlike the case of associative containers, emulating <code>std::list</code> | |
| 218 | in Boost.MultiIndex does not add any significant functionality, so the following | |
| 219 | is presented merely for completeness sake. | |
| 220 | </p> | |
| 221 | ||
| 222 | <p> | |
| 223 | Much as with standard maps, the main difficulty to overcome when emulating | |
| 224 | <code>std::list</code> derives from the constant nature of elements of a | |
| 225 | <code>multi_index_container</code>. Again, some sort of adaption class is needed, like | |
| 226 | for instance the following: | |
| 227 | </p> | |
| 228 | ||
| 229 | <blockquote><pre> | |
| 230 | <span class=keyword>template</span> <span class=special><</span><span class=keyword>typename</span> <span class=identifier>T</span><span class=special>></span> | |
| 231 | <span class=keyword>struct</span> <span class=identifier>mutable_value</span> | |
| 232 | <span class=special>{</span> | |
| 233 | <span class=identifier>mutable_value</span><span class=special>(</span><span class=keyword>const</span> <span class=identifier>T</span><span class=special>&</span> <span class=identifier>t</span><span class=special>):</span><span class=identifier>t</span><span class=special>(</span><span class=identifier>t</span><span class=special>){}</span> | |
| 234 | <span class=keyword>operator</span> <span class=identifier>T</span><span class=special>&()</span><span class=keyword>const</span><span class=special>{</span><span class=keyword>return</span> <span class=identifier>t</span><span class=special>;}</span> | |
| 235 | ||
| 236 | <span class=keyword>private</span><span class=special>:</span> | |
| 237 | <span class=keyword>mutable</span> <span class=identifier>T</span> <span class=identifier>t</span><span class=special>;</span> | |
| 238 | <span class=special>};</span> | |
| 239 | </pre></blockquote> | |
| 240 | ||
| 241 | <p> | |
| 242 | which allows us to use the substitution rule: | |
| 243 | </p> | |
| 244 | ||
| 245 | <blockquote><pre> | |
| 246 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>list</span><span class=special><</span><span class=identifier>T</span><span class=special>,</span><span class=identifier>Allocator</span><span class=special>></span> <span class=special>-></span> | |
| 247 | <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 248 | <span class=identifier>Element</span><span class=special>,</span> | |
| 249 | <span class=identifier>indexed_by</span><span class=special><</span><span class=identifier>sequenced</span><span class=special><></span> <span class=special>>,</span> | |
| 250 | <span class=keyword>typename</span> <span class=identifier>Allocator</span><span class=special>::</span><span class=keyword>template</span> <span class=identifier>rebind</span><span class=special><</span><span class=identifier>Element</span><span class=special>>::</span><span class=identifier>other</span> | |
| 251 | <span class=special>></span> | |
| 252 | ||
| 253 | (<span class=identifier>with</span> <span class=identifier>Element</span><span class=special>=</span><span class=identifier>mutable_value</span><span class=special><</span><span class=identifier>T</span><span class=special>></span>) | |
| 254 | </pre></blockquote> | |
| 255 | ||
| 256 | <p> | |
| 257 | or, if the default value <code>Allocator=std::allocator<T></code> is used: | |
| 258 | </p> | |
| 259 | ||
| 260 | <blockquote><pre> | |
| 261 | <span class=identifier>std</span><span class=special>::</span><span class=identifier>list</span><span class=special><</span><span class=identifier>T</span><span class=special>></span> <span class=special>-></span> | |
| 262 | <span class=identifier>multi_index_container</span><span class=special><</span><span class=identifier>mutable_value</span><span class=special><</span><span class=identifier>T</span><span class=special>>,</span><span class=identifier>indexed_by</span><span class=special><</span><span class=identifier>sequenced</span><span class=special><></span> <span class=special>></span> <span class=special>></span> | |
| 263 | </pre></blockquote> | |
| 264 | ||
| 265 | <h2><a name="metaprogrammming">Metaprogramming and <code>multi_index_container</code></a></h2> | |
| 266 | ||
| 267 | <p> | |
| 268 | Boost.MultiIndex provides a number of facilities intended to allow the analysis and | |
| 269 | synthesis of <code>multi_index_container</code> instantiations by | |
| 270 | <a href="../../../../libs/mpl/doc/index.html">MPL</a> metaprograms. | |
| 271 | </p> | |
| 272 | ||
| 273 | <h3><a name="mpl_analysis">MPL analysis</a></h3> | |
| 274 | ||
| 275 | <p> | |
| 276 | Given a <code>multi_index_container</code> instantiation, the following nested types are | |
| 277 | provided for compile-time inspection of the various types occurring in the | |
| 278 | definition of the <code>multi_index_container</code>: | |
| 279 | <ul> | |
| 280 | <li><code>index_specifier_type_list</code>,</li> | |
| 281 | <li><code>index_type_list</code>,</li> | |
| 282 | <li><code>iterator_type_list</code>,</li> | |
| 283 | <li><code>const_iterator_type_list</code>.</li> | |
| 284 | </ul> | |
| 285 | Each of these types is an MPL sequence with as many elements as indices | |
| 286 | comprise the <code>multi_index_container</code>: for instance, the <code>n</code>-th | |
| 287 | element of <code>iterator_type_list</code> is the same as | |
| 288 | <code>nth_index<n>::type::iterator</code>. | |
| 289 | </p> | |
| 290 | ||
| 291 | <p> | |
| 292 | A subtle but important distinction exists between | |
| 293 | <code>index_specifier_type_list</code> and <code>index_type_list</code>: | |
| 294 | the former typelist holds the index <i>specifiers</i> | |
| 295 | with which the <code>multi_index_container</code> instantiation was defined, | |
| 296 | while the latter gives access to the actual implementation classes | |
| 297 | corresponding to each specifier. An example will help to clarify | |
| 298 | this distinction. Given the instantiation: | |
| 299 | </p> | |
| 300 | ||
| 301 | <blockquote><pre> | |
| 302 | <span class=keyword>typedef</span> <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 303 | <span class=keyword>int</span><span class=special>,</span> | |
| 304 | <span class=identifier>indexed_by</span><span class=special><</span> | |
| 305 | <span class=identifier>ordered_unique</span><span class=special><</span><span class=identifier>identity</span><span class=special><</span><span class=keyword>int</span><span class=special>></span> <span class=special>>,</span> | |
| 306 | <span class=identifier>sequenced</span><span class=special><></span> | |
| 307 | <span class=special>></span> | |
| 308 | <span class=special>></span> <span class=identifier>indexed_t</span><span class=special>;</span> | |
| 309 | </pre></blockquote> | |
| 310 | ||
| 311 | <p> | |
| 312 | <code>indexed_t::index_specifier_type_list</code> is a type list with | |
| 313 | elements | |
| 314 | </p> | |
| 315 | ||
| 316 | <blockquote><pre> | |
| 317 | <span class=identifier>ordered_unique</span><span class=special><</span><span class=identifier>identity</span><span class=special><</span><span class=keyword>int</span><span class=special>></span> <span class=special>></span> | |
| 318 | <span class=identifier>sequenced</span><span class=special><></span> | |
| 319 | </pre></blockquote> | |
| 320 | ||
| 321 | <p> | |
| 322 | while <code>indexed_t::index_type_list</code> holds the types | |
| 323 | </p> | |
| 324 | ||
| 325 | <blockquote><pre> | |
| 326 | <span class=identifier>multi_index_container</span><span class=special>::</span><span class=identifier>nth_type</span><span class=special><</span><span class=number>0</span><span class=special>>::</span><span class=identifier>type</span> | |
| 327 | <span class=identifier>multi_index_container</span><span class=special>::</span><span class=identifier>nth_type</span><span class=special><</span><span class=number>1</span><span class=special>>::</span><span class=identifier>type</span> | |
| 328 | </pre></blockquote> | |
| 329 | ||
| 330 | <p> | |
| 331 | so the typelists are radically different. Check the | |
| 332 | <a href="../reference/multi_index_container.html#types">reference</a> | |
| 333 | for the exact MPL sequence concepts modeled by these type lists. | |
| 334 | </p> | |
| 335 | ||
| 336 | <h3><a name="mpl_synthesis">MPL synthesis</a></h3> | |
| 337 | ||
| 338 | <p> | |
| 339 | Although typically indices are specified by means of the | |
| 340 | <code>indexed_by</code> construct, actually any MPL sequence of | |
| 341 | index specifiers can be provided instead: | |
| 342 | </p> | |
| 343 | ||
| 344 | <blockquote><pre> | |
| 345 | <span class=keyword>typedef</span> <span class=identifier>mpl</span><span class=special>::</span><span class=identifier>vector</span><span class=special><</span><span class=identifier>ordered_unique</span><span class=special><</span><span class=identifier>identity</span><span class=special><</span><span class=keyword>int</span><span class=special>></span> <span class=special>>,</span><span class=identifier>sequenced</span><span class=special><></span> <span class=special>></span> <span class=identifier>index_list_t</span><span class=special>;</span> | |
| 346 | ||
| 347 | <span class=keyword>typedef</span> <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 348 | <span class=keyword>int</span><span class=special>,</span> | |
| 349 | <span class=identifier>index_list_t</span> | |
| 350 | <span class=special>></span> <span class=identifier>indexed_t</span><span class=special>;</span> | |
| 351 | </pre></blockquote> | |
| 352 | ||
| 353 | <p> | |
| 354 | This possibility enables the synthesis of instantiations of | |
| 355 | <code>multi_index_container</code> through MPL metaprograms, as the following | |
| 356 | example shows: | |
| 357 | </p> | |
| 358 | ||
| 359 | <blockquote><pre> | |
| 360 | <span class=comment>// original multi_index_container instantiation</span> | |
| 361 | <span class=keyword>typedef</span> <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 362 | <span class=keyword>int</span><span class=special>,</span> | |
| 363 | <span class=identifier>indexed_by</span><span class=special><</span> | |
| 364 | <span class=identifier>ordered_unique</span><span class=special><</span><span class=identifier>identity</span><span class=special><</span><span class=keyword>int</span><span class=special>></span> <span class=special>></span> | |
| 365 | <span class=special>></span> | |
| 366 | <span class=special>></span> <span class=identifier>indexed_t1</span><span class=special>;</span> | |
| 367 | ||
| 368 | <span class=comment>// we take its index list and add an index</span> | |
| 369 | <span class=keyword>typedef</span> <span class=identifier>boost</span><span class=special>::</span><span class=identifier>mpl</span><span class=special>::</span><span class=identifier>push_front</span><span class=special><</span> | |
| 370 | <span class=identifier>indexed_t1</span><span class=special>::</span><span class=identifier>index_specifier_type_list</span><span class=special>,</span> | |
| 371 | <span class=identifier>sequenced</span><span class=special><></span> | |
| 372 | <span class=special>>::</span><span class=identifier>type</span> <span class=identifier>index_list_t</span><span class=special>;</span> | |
| 373 | ||
| 374 | <span class=comment>// augmented multi_index_container</span> | |
| 375 | <span class=keyword>typedef</span> <span class=identifier>multi_index_container</span><span class=special><</span> | |
| 376 | <span class=keyword>int</span><span class=special>,</span> | |
| 377 | <span class=identifier>index_list_t</span> | |
| 378 | <span class=special>></span> <span class=identifier>indexed_t2</span><span class=special>;</span> | |
| 379 | </pre></blockquote> | |
| 380 | ||
| 381 | <hr> | |
| 382 | ||
| 383 | <div class="prev_link"><a href="debug.html"><img src="../prev.gif" alt="debugging support" border="0"><br> | |
| 384 | Debugging support | |
| 385 | </a></div> | |
| 386 | <div class="up_link"><a href="index.html"><img src="../up.gif" alt="Boost.MultiIndex tutorial" border="0"><br> | |
| 387 | Boost.MultiIndex tutorial | |
| 388 | </a></div> | |
| 389 | <div class="next_link"><a href="../reference/index.html"><img src="../next.gif" alt="Boost.MultiIndex reference" border="0"><br> | |
| 390 | Boost.MultiIndex reference | |
| 391 | </a></div><br clear="all" style="clear: all;"> | |
| 392 | ||
| 393 | <br> | |
| 394 | ||
| 395 | <p>Revised November 7th 2008</p> | |
| 396 | ||
| 397 | <p>© Copyright 2003-2008 Joaquín M López Muñoz. | |
| 398 | Distributed under the Boost Software | |
| 399 | License, Version 1.0. (See accompanying file <a href="../../../../LICENSE_1_0.txt"> | |
| 400 | LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt"> | |
| 401 | http://www.boost.org/LICENSE_1_0.txt</a>) | |
| 402 | </p> | |
| 403 | ||
| 404 | </body> | |
| 405 | </html> |