1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Main features</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../container.html" title="Chapter 9. Boost.Container">
<link rel="prev" href="../container.html" title="Chapter 9. Boost.Container">
<link rel="next" href="exception_handling.html" title="Boost.Container and C++ exceptions">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
<td align="center"><a href="../../../index.html">Home</a></td>
<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="../container.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../container.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exception_handling.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="container.main_features"></a><a class="link" href="main_features.html" title="Main features">Main features</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="main_features.html#container.main_features.move_emplace">Efficient insertion</a></span></dt>
<dt><span class="section"><a href="main_features.html#container.main_features.containers_of_incomplete_types">Containers
of Incomplete Types</a></span></dt>
<dt><span class="section"><a href="main_features.html#container.main_features.scary_iterators">SCARY iterators</a></span></dt>
<dt><span class="section"><a href="main_features.html#container.main_features.other_features">Other features</a></span></dt>
</dl></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.main_features.move_emplace"></a><a class="link" href="main_features.html#container.main_features.move_emplace" title="Efficient insertion">Efficient insertion</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="main_features.html#container.main_features.move_emplace.move_containers">Move-aware
containers</a></span></dt>
<dt><span class="section"><a href="main_features.html#container.main_features.move_emplace.emplace">Emplace:
Placement insertion</a></span></dt>
</dl></div>
<p>
Move semantics and placement insertion are two features brought by C++11
containers that can have a very positive impact in your C++ applications.
Boost.Container implements both techniques both for C++11 and C++03 compilers.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="container.main_features.move_emplace.move_containers"></a><a class="link" href="main_features.html#container.main_features.move_emplace.move_containers" title="Move-aware containers">Move-aware
containers</a>
</h4></div></div></div>
<p>
All containers offered by <span class="bold"><strong>Boost.Container</strong></span>
can store movable-only types and actual requirements for <code class="computeroutput"><span class="identifier">value_type</span></code> depend on each container operations.
Following C++11 requirements even for C++03 compilers, many operations
now require movable or default constructible types instead of just copy
constructible types.
</p>
<p>
Containers themselves are also movable, with no-throw guarantee if allocator
or predicate (if present) copy operations are no-throw. This allows high
performance operations when transferring data between vectors. Let's see
an example:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">move</span><span class="special">/</span><span class="identifier">utility_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span>
<span class="comment">//Non-copyable class</span>
<span class="keyword">class</span> <span class="identifier">non_copyable</span>
<span class="special">{</span>
<span class="identifier">BOOST_MOVABLE_BUT_NOT_COPYABLE</span><span class="special">(</span><span class="identifier">non_copyable</span><span class="special">)</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">non_copyable</span><span class="special">(){}</span>
<span class="identifier">non_copyable</span><span class="special">(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">non_copyable</span><span class="special">))</span> <span class="special">{}</span>
<span class="identifier">non_copyable</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="identifier">BOOST_RV_REF</span><span class="special">(</span><span class="identifier">non_copyable</span><span class="special">))</span> <span class="special">{</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;</span> <span class="special">}</span>
<span class="special">};</span>
<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
<span class="special">{</span>
<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">container</span><span class="special">;</span>
<span class="comment">//Store non-copyable objects in a vector</span>
<span class="identifier">vector</span><span class="special"><</span><span class="identifier">non_copyable</span><span class="special">></span> <span class="identifier">v</span><span class="special">;</span>
<span class="identifier">non_copyable</span> <span class="identifier">nc</span><span class="special">;</span>
<span class="identifier">v</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">nc</span><span class="special">));</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
<span class="comment">//Reserve no longer needs copy-constructible</span>
<span class="identifier">v</span><span class="special">.</span><span class="identifier">reserve</span><span class="special">(</span><span class="number">100</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">capacity</span><span class="special">()</span> <span class="special">>=</span> <span class="number">100</span><span class="special">);</span>
<span class="comment">//This resize overload only needs movable and default constructible</span>
<span class="identifier">v</span><span class="special">.</span><span class="identifier">resize</span><span class="special">(</span><span class="number">200</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">200</span><span class="special">);</span>
<span class="comment">//Containers are also movable</span>
<span class="identifier">vector</span><span class="special"><</span><span class="identifier">non_copyable</span><span class="special">></span> <span class="identifier">v_other</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v</span><span class="special">));</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v_other</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">200</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">.</span><span class="identifier">empty</span><span class="special">());</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="container.main_features.move_emplace.emplace"></a><a class="link" href="main_features.html#container.main_features.move_emplace.emplace" title="Emplace: Placement insertion">Emplace:
Placement insertion</a>
</h4></div></div></div>
<p>
All containers offered by <span class="bold"><strong>Boost.Container</strong></span>
implement placement insertion, which means that objects can be built directly
into the container from user arguments without creating any temporary object.
For compilers without variadic templates support placement insertion is
emulated up to a finite (10) number of arguments.
</p>
<p>
Expensive to move types are perfect candidates emplace functions and in
case of node containers (<code class="computeroutput"><a class="link" href="../boost/container/list.html" title="Class template list">list</a></code>,
<code class="computeroutput"><a class="link" href="../boost/container/set.html" title="Class template set">set</a></code>, ...) emplace allows
storing non-movable and non-copyable types in containers! Let's see an
example:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span>
<span class="comment">//Non-copyable and non-movable class</span>
<span class="keyword">class</span> <span class="identifier">non_copy_movable</span>
<span class="special">{</span>
<span class="identifier">non_copy_movable</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">non_copy_movable</span> <span class="special">&);</span>
<span class="identifier">non_copy_movable</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="identifier">non_copy_movable</span> <span class="special">&);</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">non_copy_movable</span><span class="special">(</span><span class="keyword">int</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="special">{}</span>
<span class="special">};</span>
<span class="keyword">int</span> <span class="identifier">main</span> <span class="special">()</span>
<span class="special">{</span>
<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">container</span><span class="special">;</span>
<span class="comment">//Store non-copyable and non-movable objects in a list</span>
<span class="identifier">list</span><span class="special"><</span><span class="identifier">non_copy_movable</span><span class="special">></span> <span class="identifier">l</span><span class="special">;</span>
<span class="identifier">non_copy_movable</span> <span class="identifier">ncm</span><span class="special">;</span>
<span class="comment">//A new element will be built calling non_copy_movable(int) contructor</span>
<span class="identifier">l</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="number">0</span><span class="special">);</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
<span class="comment">//A new element will be value initialized</span>
<span class="identifier">l</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">begin</span><span class="special">());</span>
<span class="identifier">assert</span><span class="special">(</span><span class="identifier">l</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">2</span><span class="special">);</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.main_features.containers_of_incomplete_types"></a><a class="link" href="main_features.html#container.main_features.containers_of_incomplete_types" title="Containers of Incomplete Types">Containers
of Incomplete Types</a>
</h3></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="main_features.html#container.main_features.containers_of_incomplete_types.recursive_containers">Recursive
containers</a></span></dt>
<dt><span class="section"><a href="main_features.html#container.main_features.containers_of_incomplete_types.type_erasure">Type
Erasure</a></span></dt>
</dl></div>
<p>
Incomplete types allow <a href="http://en.wikipedia.org/wiki/Type_erasure" target="_top"><span class="bold"><strong>type erasure </strong></span></a> and <a href="http://en.wikipedia.org/wiki/Recursive_data_type" target="_top"><span class="bold"><strong>recursive data types</strong></span></a>, and C and C++ programmers
have been using it for years to build complex data structures, like tree
structures where a node may have an arbitrary number of children.
</p>
<p>
What about standard containers? Containers of incomplete types have been
under discussion for a long time, as explained in Matt Austern's great article
(<a href="http://drdobbs.com/184403814" target="_top"><span class="bold"><strong>The Standard
Librarian: Containers of Incomplete Types</strong></span></a>):
</p>
<p>
<span class="quote">“<span class="quote"><span class="emphasis"><em>Unlike most of my columns, this one is about something you
can't do with the C++ Standard library: put incomplete types in one of the
standard containers. This column explains why you might want to do this,
why the standardization committee banned it even though they knew it was
useful, and what you might be able to do to get around the restriction.</em></span></span>”</span>
</p>
<p>
<span class="quote">“<span class="quote"><span class="emphasis"><em>In 1997, shortly before the C++ Standard was completed,
the standardization committee received a query: Is it possible to create
standard containers with incomplete types? It took a while for the committee
to understand the question. What would such a thing even mean, and why on
earth would you ever want to do it? The committee eventually worked it out
and came up with an answer to the question. (Just so you don't have to skip
ahead to the end, the answer is "no.") But the question is much
more interesting than the answer: it points to a useful, and insufficiently
discussed, programming technique. The standard library doesn't directly support
that technique, but the two can be made to coexist.</em></span></span>”</span>
</p>
<p>
<span class="quote">“<span class="quote"><span class="emphasis"><em>In a future revision of C++, it might make sense to relax
the restriction on instantiating standard library templates with incomplete
types. Clearly, the general prohibition should stay in place - instantiating
templates with incomplete types is a delicate business, and there are too
many classes in the standard library where it would make no sense. But perhaps
it should be relaxed on a case-by-case basis, and <code class="computeroutput"><span class="identifier">vector</span></code>
looks like a good candidate for such special-case treatment: it's the one
standard container class where there are good reasons to instantiate it with
an incomplete type and where Standard Library implementors want to make it
work. As of today, in fact, implementors would have to go out of their way
to prohibit it!</em></span></span>”</span>
</p>
<p>
C++11 standard is also cautious about incomplete types and STL: <span class="quote">“<span class="quote"><span class="emphasis"><em>17.6.4.8
Other functions (...) 2. the effects are undefined in the following cases:
(...) In particular - if an incomplete type (3.9) is used as a template argument
when instantiating a template component, unless specifically allowed for
that component</em></span></span>”</span>.
</p>
<p>
Fortunately all <span class="bold"><strong>Boost.Container</strong></span> containers
except <code class="computeroutput"><a class="link" href="../boost/container/static_vector.html" title="Class template static_vector">static_vector</a></code>
and <code class="computeroutput"><a class="link" href="../boost/container/small_vector.html" title="Class template small_vector">small_vector</a></code>
and <code class="computeroutput"><a class="link" href="../boost/container/basic_string.html" title="Class template basic_string">basic_string</a></code>
are designed to support incomplete types. <code class="computeroutput"><a class="link" href="../boost/container/static_vector.html" title="Class template static_vector">static_vector</a></code>
and <code class="computeroutput"><a class="link" href="../boost/container/small_vector.html" title="Class template small_vector">small_vector</a></code>
are special because they statically allocates memory for <code class="computeroutput"><span class="identifier">value_type</span></code>
and this requires complete types. <code class="computeroutput"><a class="link" href="../boost/container/basic_string.html" title="Class template basic_string">basic_string</a></code>
implements Small String Optimization which also requires complete types.
</p>
<p>
<span class="bold"><strong>Boost.Container</strong></span> containers supporting incomplete
types also support instantiating iterators to those incomplete elements.
</p>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="container.main_features.containers_of_incomplete_types.recursive_containers"></a><a class="link" href="main_features.html#container.main_features.containers_of_incomplete_types.recursive_containers" title="Recursive containers">Recursive
containers</a>
</h4></div></div></div>
<p>
Most <span class="bold"><strong>Boost.Container</strong></span> containers can be
used to define recursive containers:
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">stable_vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">deque</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">list</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">map</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">string</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">container</span><span class="special">;</span>
<span class="keyword">struct</span> <span class="identifier">data</span>
<span class="special">{</span>
<span class="keyword">int</span> <span class="identifier">i_</span><span class="special">;</span>
<span class="comment">//A vector holding still undefined class 'data'</span>
<span class="identifier">vector</span><span class="special"><</span><span class="identifier">data</span><span class="special">></span> <span class="identifier">v_</span><span class="special">;</span>
<span class="identifier">vector</span><span class="special"><</span><span class="identifier">data</span><span class="special">>::</span><span class="identifier">iterator</span> <span class="identifier">vi_</span><span class="special">;</span>
<span class="comment">//A stable_vector holding still undefined class 'data'</span>
<span class="identifier">stable_vector</span><span class="special"><</span><span class="identifier">data</span><span class="special">></span> <span class="identifier">sv_</span><span class="special">;</span>
<span class="identifier">stable_vector</span><span class="special"><</span><span class="identifier">data</span><span class="special">>::</span><span class="identifier">iterator</span> <span class="identifier">svi_</span><span class="special">;</span>
<span class="comment">//A stable_vector holding still undefined class 'data'</span>
<span class="identifier">deque</span><span class="special"><</span><span class="identifier">data</span><span class="special">></span> <span class="identifier">d_</span><span class="special">;</span>
<span class="identifier">deque</span><span class="special"><</span><span class="identifier">data</span><span class="special">>::</span><span class="identifier">iterator</span> <span class="identifier">di_</span><span class="special">;</span>
<span class="comment">//A list holding still undefined 'data'</span>
<span class="identifier">list</span><span class="special"><</span><span class="identifier">data</span><span class="special">></span> <span class="identifier">l_</span><span class="special">;</span>
<span class="identifier">list</span><span class="special"><</span><span class="identifier">data</span><span class="special">>::</span><span class="identifier">iterator</span> <span class="identifier">li_</span><span class="special">;</span>
<span class="comment">//A map holding still undefined 'data'</span>
<span class="identifier">map</span><span class="special"><</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">data</span><span class="special">></span> <span class="identifier">m_</span><span class="special">;</span>
<span class="identifier">map</span><span class="special"><</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">data</span><span class="special">>::</span><span class="identifier">iterator</span> <span class="identifier">mi_</span><span class="special">;</span>
<span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special"><(</span><span class="keyword">const</span> <span class="identifier">data</span> <span class="special">&</span><span class="identifier">l</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">data</span> <span class="special">&</span><span class="identifier">r</span><span class="special">)</span>
<span class="special">{</span> <span class="keyword">return</span> <span class="identifier">l</span><span class="special">.</span><span class="identifier">i_</span> <span class="special"><</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">i_</span><span class="special">;</span> <span class="special">}</span>
<span class="special">};</span>
<span class="keyword">struct</span> <span class="identifier">tree_node</span>
<span class="special">{</span>
<span class="identifier">string</span> <span class="identifier">name</span><span class="special">;</span>
<span class="identifier">string</span> <span class="identifier">value</span><span class="special">;</span>
<span class="comment">//children nodes of this node</span>
<span class="identifier">list</span><span class="special"><</span><span class="identifier">tree_node</span><span class="special">></span> <span class="identifier">children_</span><span class="special">;</span>
<span class="identifier">list</span><span class="special"><</span><span class="identifier">tree_node</span><span class="special">>::</span><span class="identifier">iterator</span> <span class="identifier">selected_child_</span><span class="special">;</span>
<span class="special">};</span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="comment">//a container holding a recursive data type</span>
<span class="identifier">stable_vector</span><span class="special"><</span><span class="identifier">data</span><span class="special">></span> <span class="identifier">sv</span><span class="special">;</span>
<span class="identifier">sv</span><span class="special">.</span><span class="identifier">resize</span><span class="special">(</span><span class="number">100</span><span class="special">);</span>
<span class="comment">//Let's build a tree based in</span>
<span class="comment">//a recursive data type</span>
<span class="identifier">tree_node</span> <span class="identifier">root</span><span class="special">;</span>
<span class="identifier">root</span><span class="special">.</span><span class="identifier">name</span> <span class="special">=</span> <span class="string">"root"</span><span class="special">;</span>
<span class="identifier">root</span><span class="special">.</span><span class="identifier">value</span> <span class="special">=</span> <span class="string">"root_value"</span><span class="special">;</span>
<span class="identifier">root</span><span class="special">.</span><span class="identifier">children_</span><span class="special">.</span><span class="identifier">resize</span><span class="special">(</span><span class="number">7</span><span class="special">);</span>
<span class="identifier">root</span><span class="special">.</span><span class="identifier">selected_child_</span> <span class="special">=</span> <span class="identifier">root</span><span class="special">.</span><span class="identifier">children_</span><span class="special">.</span><span class="identifier">begin</span><span class="special">();</span>
<span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h4 class="title">
<a name="container.main_features.containers_of_incomplete_types.type_erasure"></a><a class="link" href="main_features.html#container.main_features.containers_of_incomplete_types.type_erasure" title="Type Erasure">Type
Erasure</a>
</h4></div></div></div>
<p>
Containers of incomplete types are useful to break header file dependencies
and improve compilation types. With Boost.Container, you can write a header
file defining a class with containers of incomplete types as data members,
if you carefully put all the implementation details that require knowing
the size of the <code class="computeroutput"><span class="identifier">value_type</span></code>
in your implementation file:
</p>
<p>
In this header file we define a class (<code class="computeroutput"><span class="identifier">MyClassHolder</span><span class="special">)</span></code> that holds a <code class="computeroutput"><span class="identifier">vector</span></code>
of an incomplete type (<code class="computeroutput"><span class="identifier">MyClass</span></code>)
that it's only forward declared.
</p>
<p>
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">container</span><span class="special">/</span><span class="identifier">vector</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
<span class="comment">//MyClassHolder.h</span>
<span class="comment">//We don't need to include "MyClass.h"</span>
<span class="comment">//to store vector<MyClass></span>
<span class="keyword">class</span> <span class="identifier">MyClass</span><span class="special">;</span>
<span class="keyword">class</span> <span class="identifier">MyClassHolder</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="keyword">void</span> <span class="identifier">AddNewObject</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">o</span><span class="special">);</span>
<span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span> <span class="identifier">GetLastObject</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="special">::</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">container</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">></span> <span class="identifier">vector_</span><span class="special">;</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
Then we can define <code class="computeroutput"><span class="identifier">MyClass</span></code>
in its own header file.
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">//MyClass.h</span>
<span class="keyword">class</span> <span class="identifier">MyClass</span>
<span class="special">{</span>
<span class="keyword">private</span><span class="special">:</span>
<span class="keyword">int</span> <span class="identifier">value_</span><span class="special">;</span>
<span class="keyword">public</span><span class="special">:</span>
<span class="identifier">MyClass</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">val</span> <span class="special">=</span> <span class="number">0</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">value_</span><span class="special">(</span><span class="identifier">val</span><span class="special">){}</span>
<span class="keyword">friend</span> <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">==(</span><span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">l</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">r</span><span class="special">)</span>
<span class="special">{</span> <span class="keyword">return</span> <span class="identifier">l</span><span class="special">.</span><span class="identifier">value_</span> <span class="special">==</span> <span class="identifier">r</span><span class="special">.</span><span class="identifier">value_</span><span class="special">;</span> <span class="special">}</span>
<span class="comment">//...</span>
<span class="special">};</span>
</pre>
<p>
</p>
<p>
And include it only in the implementation file of <code class="computeroutput"><span class="identifier">MyClassHolder</span></code>
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">//MyClassHolder.cpp</span>
<span class="preprocessor">#include</span> <span class="string">"MyClassHolder.h"</span>
<span class="comment">//In the implementation MyClass must be a complete</span>
<span class="comment">//type so we include the appropriate header</span>
<span class="preprocessor">#include</span> <span class="string">"MyClass.h"</span>
<span class="keyword">void</span> <span class="identifier">MyClassHolder</span><span class="special">::</span><span class="identifier">AddNewObject</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span><span class="identifier">o</span><span class="special">)</span>
<span class="special">{</span> <span class="identifier">vector_</span><span class="special">.</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">o</span><span class="special">);</span> <span class="special">}</span>
<span class="keyword">const</span> <span class="identifier">MyClass</span> <span class="special">&</span> <span class="identifier">MyClassHolder</span><span class="special">::</span><span class="identifier">GetLastObject</span><span class="special">()</span> <span class="keyword">const</span>
<span class="special">{</span> <span class="keyword">return</span> <span class="identifier">vector_</span><span class="special">.</span><span class="identifier">back</span><span class="special">();</span> <span class="special">}</span>
</pre>
<p>
</p>
<p>
Finally, we can just compile, link, and run!
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">//Main.cpp</span>
<span class="preprocessor">#include</span> <span class="string">"MyClassHolder.h"</span>
<span class="preprocessor">#include</span> <span class="string">"MyClass.h"</span>
<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span>
<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
<span class="special">{</span>
<span class="identifier">MyClass</span> <span class="identifier">mc</span><span class="special">(</span><span class="number">7</span><span class="special">);</span>
<span class="identifier">MyClassHolder</span> <span class="identifier">myclassholder</span><span class="special">;</span>
<span class="identifier">myclassholder</span><span class="special">.</span><span class="identifier">AddNewObject</span><span class="special">(</span><span class="identifier">mc</span><span class="special">);</span>
<span class="keyword">return</span> <span class="identifier">myclassholder</span><span class="special">.</span><span class="identifier">GetLastObject</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">mc</span> <span class="special">?</span> <span class="number">0</span> <span class="special">:</span> <span class="number">1</span><span class="special">;</span>
<span class="special">}</span>
</pre>
<p>
</p>
</div>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.main_features.scary_iterators"></a><a class="link" href="main_features.html#container.main_features.scary_iterators" title="SCARY iterators">SCARY iterators</a>
</h3></div></div></div>
<p>
The paper N2913, titled <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2913.pdf%2c" target="_top">SCARY
Iterator Assignment and Initialization</a>, proposed a requirement that
a standard container's iterator types have no dependency on any type argument
apart from the container's <code class="computeroutput"><span class="identifier">value_type</span></code>,
<code class="computeroutput"><span class="identifier">difference_type</span></code>, <code class="computeroutput"><span class="identifier">pointer</span> <span class="identifier">type</span></code>,
and <code class="computeroutput"><span class="identifier">const_pointer</span></code> type. In
particular, according to the proposal, the types of a standard container's
iterators should not depend on the container's <code class="computeroutput"><span class="identifier">key_compare</span></code>,
<code class="computeroutput"><span class="identifier">hasher</span></code>, <code class="computeroutput"><span class="identifier">key_equal</span></code>,
or <code class="computeroutput"><span class="identifier">allocator</span></code> types.
</p>
<p>
That paper demonstrated that SCARY operations were crucial to the performant
implementation of common design patterns using STL components. It showed
that implementations that support SCARY operations reduce object code bloat
by eliminating redundant specializations of iterator and algorithm templates.
</p>
<p>
<span class="bold"><strong>Boost.Container</strong></span> containers implement SCARY
iterators so the iterator type of a container is only dependent on the <code class="computeroutput"><span class="identifier">allocator_traits</span><span class="special"><</span><span class="identifier">allocator_type</span><span class="special">>::</span><span class="identifier">pointer</span></code> type (the pointer type of the
<code class="computeroutput"><span class="identifier">value_type</span></code> to be inserted
in the container). Reference types and all other typedefs are deduced from
the pointer type using the C++11 <code class="computeroutput"><span class="identifier">pointer_traits</span></code>
utility. This leads to lower code bloat in algorithms and classes templated
on iterators.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="container.main_features.other_features"></a><a class="link" href="main_features.html#container.main_features.other_features" title="Other features">Other features</a>
</h3></div></div></div>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Default constructors don't allocate memory which improves performance
and usually implies a no-throw guarantee (if predicate's or allocator's
default constructor doesn't throw).
</li>
<li class="listitem">
Small string optimization for <code class="computeroutput"><a class="link" href="../boost/container/basic_string.html" title="Class template basic_string">basic_string</a></code>,
with an internal buffer of 11/23 bytes (32/64 bit systems) <span class="bold"><strong>without</strong></span> increasing the usual <code class="computeroutput"><span class="keyword">sizeof</span></code>
of the string (3 words).
</li>
<li class="listitem">
<code class="computeroutput"><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span><span class="special">/</span><span class="identifier">map</span></code>
containers are size optimized embedding the color bit of the red-black
tree nodes in the parent pointer.
</li>
<li class="listitem">
<code class="computeroutput"><span class="special">[</span><span class="identifier">multi</span><span class="special">]</span><span class="identifier">set</span><span class="special">/</span><span class="identifier">map</span></code>
containers use no recursive functions so stack problems are avoided.
</li>
</ul></div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2009-2017 Ion
Gaztanaga<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
</p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="../container.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../container.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exception_handling.html"><img src="../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
|
