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21<div class="titlepage"><div>
22<div><h2 class="title">
23<a name="boost_functional_factory"></a>Chapter&#160;1.&#160;Boost.Functional/Factory 1.0</h2></div>
24<div><div class="author"><h3 class="author">
25<span class="firstname">Tobias</span> <span class="surname">Schwinger</span>
26</h3></div></div>
27<div><p class="copyright">Copyright &#169; 2007, 2008 Tobias Schwinger</p></div>
28<div><div class="legalnotice">
29<a name="boost_functional_factory.legal"></a><p>
30 Distributed under the Boost Software License, Version 1.0. (See accompanying
31 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>)
32 </p>
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34</div></div>
35<div class="toc">
36<p><b>Table of Contents</b></p>
37<dl class="toc">
38<dt><span class="section"><a href="index.html#boost_functional_factory.brief_description">Brief Description</a></span></dt>
39<dt><span class="section"><a href="index.html#boost_functional_factory.background">Background</a></span></dt>
40<dt><span class="section"><a href="index.html#boost_functional_factory.reference">Reference</a></span></dt>
41<dt><span class="section"><a href="index.html#boost_functional_factory.acknowledgements">Acknowledgements</a></span></dt>
42<dt><span class="section"><a href="index.html#boost_functional_factory.references">References</a></span></dt>
43</dl>
44</div>
45<div class="section">
46<div class="titlepage"><div><div><h2 class="title" style="clear: both">
47<a name="boost_functional_factory.brief_description"></a><a class="link" href="index.html#boost_functional_factory.brief_description" title="Brief Description">Brief Description</a>
48</h2></div></div></div>
49<p>
50 The template <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code> lets you encapsulate a <code class="computeroutput"><span class="keyword">new</span></code> expression as a function object, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code>
51 encapsulates a constructor invocation without <code class="computeroutput"><span class="keyword">new</span></code>.
52 </p>
53<pre class="programlisting"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code><span class="special">&lt;</span><span class="identifier">T</span><span class="special">*&gt;()(</span><span class="identifier">arg1</span><span class="special">,</span><span class="identifier">arg2</span><span class="special">,</span><span class="identifier">arg3</span><span class="special">)</span>
54<span class="comment">// same as new T(arg1,arg2,arg3)</span>
55
56<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code><span class="special">&lt;</span><span class="identifier">T</span><span class="special">&gt;()(</span><span class="identifier">arg1</span><span class="special">,</span><span class="identifier">arg2</span><span class="special">,</span><span class="identifier">arg3</span><span class="special">)</span>
57<span class="comment">// same as T(arg1,arg2,arg3)</span>
58</pre>
59<p>
60 For technical reasons the arguments to the function objects have to be LValues.
61 A factory that also accepts RValues can be composed using the <a href="http://www.boost.org/libs/functional/forward/doc/index.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">forward_adapter</span></code></a>
62 or <a href="http://www.boost.org/libs/bind/bind.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span></code></a>.
63 </p>
64</div>
65<div class="section">
66<div class="titlepage"><div><div><h2 class="title" style="clear: both">
67<a name="boost_functional_factory.background"></a><a class="link" href="index.html#boost_functional_factory.background" title="Background">Background</a>
68</h2></div></div></div>
69<p>
70 In traditional Object Oriented Programming a Factory is an object implementing
71 an interface of one or more methods that construct objects conforming to known
72 interfaces.
73 </p>
74<pre class="programlisting"><span class="comment">// assuming a_concrete_class and another_concrete_class are derived</span>
75<span class="comment">// from an_abstract_class</span>
76
77<span class="keyword">class</span> <span class="identifier">a_factory</span>
78<span class="special">{</span>
79 <span class="keyword">public</span><span class="special">:</span>
80 <span class="keyword">virtual</span> <span class="identifier">an_abstract_class</span><span class="special">*</span> <span class="identifier">create</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
81 <span class="keyword">virtual</span> <span class="special">~</span><span class="identifier">a_factory</span><span class="special">()</span> <span class="special">{</span> <span class="special">}</span>
82<span class="special">};</span>
83
84<span class="keyword">class</span> <span class="identifier">a_concrete_factory</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">a_factory</span>
85<span class="special">{</span>
86 <span class="keyword">public</span><span class="special">:</span>
87 <span class="keyword">virtual</span> <span class="identifier">an_abstract_class</span><span class="special">*</span> <span class="identifier">create</span><span class="special">()</span> <span class="keyword">const</span>
88 <span class="special">{</span>
89 <span class="keyword">return</span> <span class="keyword">new</span> <span class="identifier">a_concrete_class</span><span class="special">();</span>
90 <span class="special">}</span>
91<span class="special">};</span>
92
93<span class="keyword">class</span> <span class="identifier">another_concrete_factory</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">a_factory</span>
94<span class="special">{</span>
95 <span class="keyword">public</span><span class="special">:</span>
96 <span class="keyword">virtual</span> <span class="identifier">an_abstract_class</span><span class="special">*</span> <span class="identifier">create</span><span class="special">()</span> <span class="keyword">const</span>
97 <span class="special">{</span>
98 <span class="keyword">return</span> <span class="keyword">new</span> <span class="identifier">another_concrete_class</span><span class="special">();</span>
99 <span class="special">}</span>
100<span class="special">};</span>
101
102<span class="comment">// [...]</span>
103
104<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
105<span class="special">{</span>
106 <a href="http://www.boost.org/libs/ptr_container/doc/ptr_map.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ptr_map</span></code></a><span class="special">&lt;</span><a href="http://www.sgi.com/tech/stl/string.html" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code></a><span class="special">,</span><span class="identifier">a_factory</span><span class="special">&gt;</span> <span class="identifier">factories</span><span class="special">;</span>
107
108 <span class="comment">// [...]</span>
109
110 <span class="identifier">factories</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="string">"a_name"</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">auto_ptr</span><span class="special">&lt;</span><span class="identifier">a_factory</span><span class="special">&gt;(</span>
111 <span class="keyword">new</span> <span class="identifier">a_concrete_factory</span><span class="special">));</span>
112 <span class="identifier">factories</span><span class="special">.</span><span class="identifier">insert</span><span class="special">(</span><span class="string">"another_name"</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">auto_ptr</span><span class="special">&lt;</span><span class="identifier">a_factory</span><span class="special">&gt;(</span>
113 <span class="keyword">new</span> <span class="identifier">another_concrete_factory</span><span class="special">));</span>
114
115 <span class="comment">// [...]</span>
116
117 <span class="identifier">std</span><span class="special">::</span><span class="identifier">auto_ptr</span><span class="special">&lt;</span><span class="identifier">an_abstract_class</span><span class="special">&gt;</span> <span class="identifier">x</span><span class="special">(</span><span class="identifier">factories</span><span class="special">.</span><span class="identifier">at</span><span class="special">(</span><span class="identifier">some_name</span><span class="special">).</span><span class="identifier">create</span><span class="special">());</span>
118
119 <span class="comment">// [...]</span>
120<span class="special">}</span>
121</pre>
122<p>
123 This approach has several drawbacks. The most obvious one is that there is
124 lots of boilerplate code. In other words there is too much code to express
125 a rather simple intention. We could use templates to get rid of some of it
126 but the approach remains inflexible:
127 </p>
128<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
129<li class="listitem">
130 We may want a factory that takes some arguments that are forwarded to the
131 constructor,
132 </li>
133<li class="listitem">
134 we will probably want to use smart pointers,
135 </li>
136<li class="listitem">
137 we may want several member functions to create different kinds of objects,
138 </li>
139<li class="listitem">
140 we might not necessarily need a polymorphic base class for the objects,
141 </li>
142<li class="listitem">
143 as we will see, we do not need a factory base class at all,
144 </li>
145<li class="listitem">
146 we might want to just call the constructor - without <code class="computeroutput"><span class="keyword">new</span></code>
147 to create an object on the stack, and
148 </li>
149<li class="listitem">
150 finally we might want to use customized memory management.
151 </li>
152</ul></div>
153<p>
154 Experience has shown that using function objects and generic Boost components
155 for their composition, Design Patterns that describe callback mechanisms (typically
156 requiring a high percentage of boilerplate code with pure Object Oriented methodology)
157 become implementable with just few code lines and without extra classes.
158 </p>
159<p>
160 Factories are callback mechanisms for constructors, so we provide two class
161 templates, <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code> and <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code>,
162 that encapsulate object construction via direct application of the constructor
163 and the <code class="computeroutput"><span class="keyword">new</span></code> operator, respectively.
164 </p>
165<p>
166 We let the function objects forward their arguments to the construction expressions
167 they encapsulate. Over this <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code>
168 optionally allows the use of smart pointers and <a href="http://www.sgi.com/tech/stl/concepts/allocator.html" target="_top">Allocators</a>.
169 </p>
170<p>
171 Compile-time polymorphism can be used where appropriate,
172 </p>
173<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">&gt;</span>
174<span class="keyword">void</span> <span class="identifier">do_something</span><span class="special">()</span>
175<span class="special">{</span>
176 <span class="comment">// [...]</span>
177 <span class="identifier">T</span> <span class="identifier">x</span> <span class="special">=</span> <span class="identifier">T</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">);</span>
178
179 <span class="comment">// for conceptually similar objects x we neither need virtual</span>
180 <span class="comment">// functions nor a common base class in this context.</span>
181 <span class="comment">// [...]</span>
182<span class="special">}</span>
183</pre>
184<p>
185 Now, to allow inhomogeneous signatures for the constructors of the types passed
186 in for <code class="computeroutput"><span class="identifier">T</span></code> we can use <code class="computeroutput"><span class="identifier">value_factory</span></code> and <a href="http://www.boost.org/libs/bind/bind.html" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span></code></a>
187 to normalize between them.
188 </p>
189<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ValueFactory</span> <span class="special">&gt;</span>
190<span class="keyword">void</span> <span class="identifier">do_something</span><span class="special">(</span><span class="identifier">ValueFactory</span> <span class="identifier">make_obj</span> <span class="special">=</span> <span class="identifier">ValueFactory</span><span class="special">())</span>
191<span class="special">{</span>
192 <span class="comment">// [...]</span>
193 <span class="keyword">typename</span> <span class="identifier">ValueFactory</span><span class="special">::</span><span class="identifier">result_type</span> <span class="identifier">x</span> <span class="special">=</span> <span class="identifier">make_obj</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">);</span>
194
195 <span class="comment">// for conceptually similar objects x we neither need virtual</span>
196 <span class="comment">// functions nor a common base class in this context.</span>
197 <span class="comment">// [...]</span>
198<span class="special">}</span>
199
200<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
201<span class="special">{</span>
202 <span class="comment">// [...]</span>
203
204 <span class="identifier">do_something</span><span class="special">(</span><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code><span class="special">&lt;</span><span class="identifier">X</span><span class="special">&gt;());</span>
205 <span class="identifier">do_something</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">bind</span><span class="special">(</span><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">value_factory</span></code><span class="special">&lt;</span><span class="identifier">Y</span><span class="special">&gt;(),</span><span class="identifier">_1</span><span class="special">,</span><span class="number">5</span><span class="special">,</span><span class="identifier">_2</span><span class="special">));</span>
206 <span class="comment">// construct X(a,b) and Y(a,5,b), respectively.</span>
207
208 <span class="comment">// [...]</span>
209<span class="special">}</span>
210</pre>
211<p>
212 Maybe we want our objects to outlive the function's scope, in this case we
213 have to use dynamic allocation;
214 </p>
215<pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">Factory</span> <span class="special">&gt;</span>
216<span class="identifier">whatever</span> <span class="identifier">do_something</span><span class="special">(</span><span class="identifier">Factory</span> <span class="identifier">new_obj</span> <span class="special">=</span> <span class="identifier">Factory</span><span class="special">())</span>
217<span class="special">{</span>
218 <span class="keyword">typename</span> <span class="identifier">Factory</span><span class="special">::</span><span class="identifier">result_type</span> <span class="identifier">ptr</span> <span class="special">=</span> <span class="identifier">new_obj</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">);</span>
219
220 <span class="comment">// again, no common base class or virtual functions needed,</span>
221 <span class="comment">// we could enforce a polymorphic base by writing e.g.</span>
222 <span class="comment">// boost::shared_ptr&lt;base&gt;</span>
223 <span class="comment">// instead of</span>
224 <span class="comment">// typename Factory::result_type</span>
225 <span class="comment">// above.</span>
226 <span class="comment">// Note that we are also free to have the type erasure happen </span>
227 <span class="comment">// somewhere else (e.g. in the constructor of this function's</span>
228 <span class="comment">// result type).</span>
229
230 <span class="comment">// [...]</span>
231<span class="special">}</span>
232
233<span class="comment">// [... call do_something like above but with __factory__ instead</span>
234<span class="comment">// of __value_factory__]</span>
235</pre>
236<p>
237 Although we might have created polymorphic objects in the previous example,
238 we have used compile time polymorphism for the factory. If we want to erase
239 the type of the factory and thus allow polymorphism at run time, we can use
240 <a href="http://www.boost.org/doc/html/function.html" target="_top">Boost.Function</a>
241 to do so. The first example can be rewritten as follows.
242 </p>
243<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special">&lt;</span> <span class="identifier">an_abstract_class</span><span class="special">*()</span> <span class="special">&gt;</span> <span class="identifier">a_factory</span><span class="special">;</span>
244
245<span class="comment">// [...]</span>
246
247<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
248<span class="special">{</span>
249 <a href="http://www.sgi.com/tech/stl/map.html" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code></a><span class="special">&lt;</span><a href="http://www.sgi.com/tech/stl/string.html" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code></a><span class="special">,</span><span class="identifier">a_factory</span><span class="special">&gt;</span> <span class="identifier">factories</span><span class="special">;</span>
250
251 <span class="comment">// [...]</span>
252
253 <span class="identifier">factories</span><span class="special">[</span><span class="string">"a_name"</span><span class="special">]</span> <span class="special">=</span> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code><span class="special">&lt;</span><span class="identifier">a_concrete_class</span><span class="special">*&gt;();</span>
254 <span class="identifier">factories</span><span class="special">[</span><span class="string">"another_name"</span><span class="special">]</span> <span class="special">=</span>
255 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">factory</span></code><span class="special">&lt;</span><span class="identifier">another_concrete_class</span><span class="special">*&gt;();</span>
256
257 <span class="comment">// [...]</span>
258<span class="special">}</span>
259</pre>
260<p>
261 Of course we can just as easy create factories that take arguments and/or return
262 <a href="http://www.boost.org/libs/smart_ptr/index.html" target="_top">Smart Pointers</a>.
263 </p>
264</div>
265<div class="section">
266<div class="titlepage"><div><div><h2 class="title" style="clear: both">
267<a name="boost_functional_factory.reference"></a><a class="link" href="index.html#boost_functional_factory.reference" title="Reference">Reference</a>
268</h2></div></div></div>
269<div class="toc"><dl class="toc">
270<dt><span class="section"><a href="index.html#boost_functional_factory.reference.value_factory">value_factory</a></span></dt>
271<dt><span class="section"><a href="index.html#boost_functional_factory.reference.factory">factory</a></span></dt>
272</dl></div>
273<div class="section">
274<div class="titlepage"><div><div><h3 class="title">
275<a name="boost_functional_factory.reference.value_factory"></a><a class="link" href="index.html#boost_functional_factory.reference.value_factory" title="value_factory">value_factory</a>
276</h3></div></div></div>
277<h5>
278<a name="boost_functional_factory.reference.value_factory.h0"></a>
279 <span class="phrase"><a name="boost_functional_factory.reference.value_factory.description"></a></span><a class="link" href="index.html#boost_functional_factory.reference.value_factory.description">Description</a>
280 </h5>
281<p>
282 Function object template that invokes the constructor of the type <code class="computeroutput"><span class="identifier">T</span></code>.
283 </p>
284<h5>
285<a name="boost_functional_factory.reference.value_factory.h1"></a>
286 <span class="phrase"><a name="boost_functional_factory.reference.value_factory.header"></a></span><a class="link" href="index.html#boost_functional_factory.reference.value_factory.header">Header</a>
287 </h5>
288<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">value_factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
289</pre>
290<h5>
291<a name="boost_functional_factory.reference.value_factory.h2"></a>
292 <span class="phrase"><a name="boost_functional_factory.reference.value_factory.synopsis"></a></span><a class="link" href="index.html#boost_functional_factory.reference.value_factory.synopsis">Synopsis</a>
293 </h5>
294<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
295<span class="special">{</span>
296 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">&gt;</span>
297 <span class="keyword">class</span> <span class="identifier">value_factory</span><span class="special">;</span>
298<span class="special">}</span>
299</pre>
300<div class="variablelist">
301<p class="title"><b>Notation</b></p>
302<dl class="variablelist">
303<dt><span class="term"><code class="computeroutput"><span class="identifier">T</span></code></span></dt>
304<dd><p>
305 an arbitrary type with at least one public constructor
306 </p></dd>
307<dt><span class="term"><code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code></span></dt>
308<dd><p>
309 argument LValues to a constructor of <code class="computeroutput"><span class="identifier">T</span></code>
310 </p></dd>
311<dt><span class="term"><code class="computeroutput"><span class="identifier">F</span></code></span></dt>
312<dd><p>
313 the type <code class="computeroutput"><span class="identifier">value_factory</span><span class="special">&lt;</span><span class="identifier">F</span><span class="special">&gt;</span></code>
314 </p></dd>
315<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code></span></dt>
316<dd><p>
317 an instance object of <code class="computeroutput"><span class="identifier">F</span></code>
318 </p></dd>
319</dl>
320</div>
321<h5>
322<a name="boost_functional_factory.reference.value_factory.h3"></a>
323 <span class="phrase"><a name="boost_functional_factory.reference.value_factory.expression_semantics"></a></span><a class="link" href="index.html#boost_functional_factory.reference.value_factory.expression_semantics">Expression
324 Semantics</a>
325 </h5>
326<div class="informaltable"><table class="table">
327<colgroup>
328<col>
329<col>
330</colgroup>
331<thead><tr>
332<th>
333 <p>
334 Expression
335 </p>
336 </th>
337<th>
338 <p>
339 Semantics
340 </p>
341 </th>
342</tr></thead>
343<tbody>
344<tr>
345<td>
346 <p>
347 <code class="computeroutput"><span class="identifier">F</span><span class="special">()</span></code>
348 </p>
349 </td>
350<td>
351 <p>
352 creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
353 </p>
354 </td>
355</tr>
356<tr>
357<td>
358 <p>
359 <code class="computeroutput"><span class="identifier">F</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span></code>
360 </p>
361 </td>
362<td>
363 <p>
364 creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
365 </p>
366 </td>
367</tr>
368<tr>
369<td>
370 <p>
371 <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>
372 </p>
373 </td>
374<td>
375 <p>
376 returns <code class="computeroutput"><span class="identifier">T</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>.
377 </p>
378 </td>
379</tr>
380<tr>
381<td>
382 <p>
383 <code class="computeroutput"><span class="identifier">F</span><span class="special">::</span><span class="identifier">result_type</span></code>
384 </p>
385 </td>
386<td>
387 <p>
388 is the type <code class="computeroutput"><span class="identifier">T</span></code>.
389 </p>
390 </td>
391</tr>
392</tbody>
393</table></div>
394<h5>
395<a name="boost_functional_factory.reference.value_factory.h4"></a>
396 <span class="phrase"><a name="boost_functional_factory.reference.value_factory.limits"></a></span><a class="link" href="index.html#boost_functional_factory.reference.value_factory.limits">Limits</a>
397 </h5>
398<p>
399 The macro BOOST_FUNCTIONAL_VALUE_FACTORY_MAX_ARITY can be defined to set
400 the maximum arity. It defaults to 10.
401 </p>
402</div>
403<div class="section">
404<div class="titlepage"><div><div><h3 class="title">
405<a name="boost_functional_factory.reference.factory"></a><a class="link" href="index.html#boost_functional_factory.reference.factory" title="factory">factory</a>
406</h3></div></div></div>
407<h5>
408<a name="boost_functional_factory.reference.factory.h0"></a>
409 <span class="phrase"><a name="boost_functional_factory.reference.factory.description"></a></span><a class="link" href="index.html#boost_functional_factory.reference.factory.description">Description</a>
410 </h5>
411<p>
412 Function object template that dynamically constructs a pointee object for
413 the type of pointer given as template argument. Smart pointers may be used
414 for the template argument, given that <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">pointee</span><span class="special">&lt;</span><span class="identifier">Pointer</span><span class="special">&gt;::</span><span class="identifier">type</span></code>
415 yields the pointee type.
416 </p>
417<p>
418 If an <a href="http://www.sgi.com/tech/stl/concepts/allocator.html" target="_top">Allocator</a>
419 is given, it is used for memory allocation and the placement form of the
420 <code class="computeroutput"><span class="keyword">new</span></code> operator is used to construct
421 the object. A function object that calls the destructor and deallocates the
422 memory with a copy of the Allocator is used for the second constructor argument
423 of <code class="computeroutput"><span class="identifier">Pointer</span></code> (thus it must
424 be a <a href="http://www.boost.org/libs/smart_ptr/index.html" target="_top">Smart Pointer</a>
425 that provides a suitable constructor, such as <a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span></code></a>).
426 </p>
427<p>
428 If a third template argument is <code class="computeroutput"><span class="identifier">factory_passes_alloc_to_smart_pointer</span></code>,
429 the allocator itself is used for the third constructor argument of <code class="computeroutput"><span class="identifier">Pointer</span></code> (<a href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm" target="_top"><code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">shared_ptr</span></code></a> then uses the allocator
430 to manage the memory of its separately allocated reference counter).
431 </p>
432<h5>
433<a name="boost_functional_factory.reference.factory.h1"></a>
434 <span class="phrase"><a name="boost_functional_factory.reference.factory.header"></a></span><a class="link" href="index.html#boost_functional_factory.reference.factory.header">Header</a>
435 </h5>
436<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">functional</span><span class="special">/</span><span class="identifier">factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
437</pre>
438<h5>
439<a name="boost_functional_factory.reference.factory.h2"></a>
440 <span class="phrase"><a name="boost_functional_factory.reference.factory.synopsis"></a></span><a class="link" href="index.html#boost_functional_factory.reference.factory.synopsis">Synopsis</a>
441 </h5>
442<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span>
443<span class="special">{</span>
444 <span class="keyword">enum</span> <span class="identifier">factory_alloc_propagation</span>
445 <span class="special">{</span>
446 <span class="identifier">factory_alloc_for_pointee_and_deleter</span><span class="special">,</span>
447 <span class="identifier">factory_passes_alloc_to_smart_pointer</span>
448 <span class="special">};</span>
449
450 <span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">typename</span> <span class="identifier">Pointer</span><span class="special">,</span>
451 <span class="keyword">class</span> <span class="identifier">Allocator</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span><span class="special">,</span>
452 <span class="identifier">factory_alloc_propagation</span> <span class="identifier">AllocProp</span> <span class="special">=</span>
453 <span class="identifier">factory_alloc_for_pointee_and_deleter</span> <span class="special">&gt;</span>
454 <span class="keyword">class</span> <span class="identifier">factory</span><span class="special">;</span>
455<span class="special">}</span>
456</pre>
457<div class="variablelist">
458<p class="title"><b>Notation</b></p>
459<dl class="variablelist">
460<dt><span class="term"><code class="computeroutput"><span class="identifier">T</span></code></span></dt>
461<dd><p>
462 an arbitrary type with at least one public constructor
463 </p></dd>
464<dt><span class="term"><code class="computeroutput"><span class="identifier">P</span></code></span></dt>
465<dd><p>
466 pointer or smart pointer to <code class="computeroutput"><span class="identifier">T</span></code>
467 </p></dd>
468<dt><span class="term"><code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code></span></dt>
469<dd><p>
470 argument LValues to a constructor of <code class="computeroutput"><span class="identifier">T</span></code>
471 </p></dd>
472<dt><span class="term"><code class="computeroutput"><span class="identifier">F</span></code></span></dt>
473<dd><p>
474 the type <code class="computeroutput"><span class="identifier">factory</span><span class="special">&lt;</span><span class="identifier">P</span><span class="special">&gt;</span></code>
475 </p></dd>
476<dt><span class="term"><code class="computeroutput"><span class="identifier">f</span></code></span></dt>
477<dd><p>
478 an instance object of <code class="computeroutput"><span class="identifier">F</span></code>
479 </p></dd>
480</dl>
481</div>
482<h5>
483<a name="boost_functional_factory.reference.factory.h3"></a>
484 <span class="phrase"><a name="boost_functional_factory.reference.factory.expression_semantics"></a></span><a class="link" href="index.html#boost_functional_factory.reference.factory.expression_semantics">Expression
485 Semantics</a>
486 </h5>
487<div class="informaltable"><table class="table">
488<colgroup>
489<col>
490<col>
491</colgroup>
492<thead><tr>
493<th>
494 <p>
495 Expression
496 </p>
497 </th>
498<th>
499 <p>
500 Semantics
501 </p>
502 </th>
503</tr></thead>
504<tbody>
505<tr>
506<td>
507 <p>
508 <code class="computeroutput"><span class="identifier">F</span><span class="special">()</span></code>
509 </p>
510 </td>
511<td>
512 <p>
513 creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
514 </p>
515 </td>
516</tr>
517<tr>
518<td>
519 <p>
520 <code class="computeroutput"><span class="identifier">F</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span></code>
521 </p>
522 </td>
523<td>
524 <p>
525 creates an object of type <code class="computeroutput"><span class="identifier">F</span></code>.
526 </p>
527 </td>
528</tr>
529<tr>
530<td>
531 <p>
532 <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span><span class="special">)</span></code>
533 </p>
534 </td>
535<td>
536 <p>
537 dynamically creates an object of type <code class="computeroutput"><span class="identifier">T</span></code>
538 using <code class="computeroutput"><span class="identifier">a0</span></code>...<code class="computeroutput"><span class="identifier">aN</span></code> as arguments for the constructor
539 invocation.
540 </p>
541 </td>
542</tr>
543<tr>
544<td>
545 <p>
546 <code class="computeroutput"><span class="identifier">F</span><span class="special">::</span><span class="identifier">result_type</span></code>
547 </p>
548 </td>
549<td>
550 <p>
551 is the type <code class="computeroutput"><span class="identifier">P</span></code> with
552 top-level cv-qualifiers removed.
553 </p>
554 </td>
555</tr>
556</tbody>
557</table></div>
558<h5>
559<a name="boost_functional_factory.reference.factory.h4"></a>
560 <span class="phrase"><a name="boost_functional_factory.reference.factory.limits"></a></span><a class="link" href="index.html#boost_functional_factory.reference.factory.limits">Limits</a>
561 </h5>
562<p>
563 The macro BOOST_FUNCTIONAL_FACTORY_MAX_ARITY can be defined to set the maximum
564 arity. It defaults to 10.
565 </p>
566</div>
567</div>
568<div class="section">
569<div class="titlepage"><div><div><h2 class="title" style="clear: both">
570<a name="boost_functional_factory.acknowledgements"></a><a class="link" href="index.html#boost_functional_factory.acknowledgements" title="Acknowledgements">Acknowledgements</a>
571</h2></div></div></div>
572<p>
573 Eric Niebler requested a function to invoke a type's constructor (with the
574 arguments supplied as a Tuple) as a Fusion feature. These Factory utilities
575 are a factored-out generalization of this idea.
576 </p>
577<p>
578 Dave Abrahams suggested Smart Pointer support for exception safety, providing
579 useful hints for the implementation.
580 </p>
581<p>
582 Joel de Guzman's documentation style was copied from Fusion.
583 </p>
584<p>
585 Further, I want to thank Peter Dimov for sharing his insights on language details
586 and their evolution.
587 </p>
588</div>
589<div class="section">
590<div class="titlepage"><div><div><h2 class="title" style="clear: both">
591<a name="boost_functional_factory.references"></a><a class="link" href="index.html#boost_functional_factory.references" title="References">References</a>
592</h2></div></div></div>
593<div class="orderedlist"><ol class="orderedlist" type="1">
594<li class="listitem">
595 <a href="http://en.wikipedia.org/wiki/Design_Patterns" target="_top">Design Patterns</a>,
596 Gamma et al. - Addison Wesley Publishing, 1995
597 </li>
598<li class="listitem">
599 <a href="http://www.sgi.com/tech/stl/" target="_top">Standard Template Library Programmer's
600 Guide</a>, Hewlett-Packard Company, 1994
601 </li>
602<li class="listitem">
603 <a href="http://www.boost.org/libs/bind/bind.html" target="_top">Boost.Bind</a>,
604 Peter Dimov, 2001-2005
605 </li>
606<li class="listitem">
607 <a href="http://www.boost.org/doc/html/function.html" target="_top">Boost.Function</a>,
608 Douglas Gregor, 2001-2004
609 </li>
610</ol></div>
611</div>
612</div>
613<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
614<td align="left"><p><small>Last revised: November 01, 2008 at 21:44:52 GMT</small></p></td>
615<td align="right"><div class="copyright-footer"></div></td>
616</tr></table>
617<hr>
618<div class="spirit-nav"></div>
619</body>
620</html>