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24 | </div> | |
25 | <div class="section"> | |
26 | <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | |
27 | <a name="boost_localfunction.examples"></a><a class="link" href="examples.html" title="Examples">Examples</a> | |
28 | </h2></div></div></div> | |
29 | <div class="toc"><dl class="toc"> | |
30 | <dt><span class="section"><a href="examples.html#boost_localfunction.examples.gcc_lambdas__without_c__11_">GCC | |
31 | Lambdas (without C++11)</a></span></dt> | |
32 | <dt><span class="section"><a href="examples.html#boost_localfunction.examples.constant_blocks">Constant | |
33 | Blocks</a></span></dt> | |
34 | <dt><span class="section"><a href="examples.html#boost_localfunction.examples.scope_exits">Scope Exits</a></span></dt> | |
35 | <dt><span class="section"><a href="examples.html#boost_localfunction.examples.boost_phoenix_functions">Boost.Phoenix | |
36 | Functions</a></span></dt> | |
37 | <dt><span class="section"><a href="examples.html#boost_localfunction.examples.closures">Closures</a></span></dt> | |
38 | <dt><span class="section"><a href="examples.html#boost_localfunction.examples.gcc_nested_functions">GCC | |
39 | Nested Functions</a></span></dt> | |
40 | <dt><span class="section"><a href="examples.html#boost_localfunction.examples.n_papers">N-Papers</a></span></dt> | |
41 | </dl></div> | |
42 | <p> | |
43 | This section lists some examples that use this library. | |
44 | </p> | |
45 | <div class="section"> | |
46 | <div class="titlepage"><div><div><h3 class="title"> | |
47 | <a name="boost_localfunction.examples.gcc_lambdas__without_c__11_"></a><a class="link" href="examples.html#boost_localfunction.examples.gcc_lambdas__without_c__11_" title="GCC Lambdas (without C++11)">GCC | |
48 | Lambdas (without C++11)</a> | |
49 | </h3></div></div></div> | |
50 | <p> | |
51 | Combing local functions with the non-standard <a href="http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html" target="_top">statement | |
52 | expression</a> extension of the GCC compiler, it is possible to implement | |
53 | lambda functions for GCC compilers even without <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
54 | support. | |
55 | </p> | |
56 | <div class="warning"><table border="0" summary="Warning"> | |
57 | <tr> | |
58 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> | |
59 | <th align="left">Warning</th> | |
60 | </tr> | |
61 | <tr><td align="left" valign="top"><p> | |
62 | This code only works on compilers that support GCC statement expression | |
63 | extension or that support <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
64 | lambda functions</a>. | |
65 | </p></td></tr> | |
66 | </table></div> | |
67 | <p> | |
68 | For example (see also <a href="../../../example/gcc_lambda.cpp" target="_top"><code class="literal">gcc_lambda.cpp</code></a> | |
69 | and <a href="../../../example/gcc_cxx11_lambda.cpp" target="_top"><code class="literal">gcc_cxx11_lambda.cpp</code></a>): | |
70 | </p> | |
71 | <div class="informaltable"><table class="table"> | |
72 | <colgroup> | |
73 | <col> | |
74 | <col> | |
75 | </colgroup> | |
76 | <thead><tr> | |
77 | <th> | |
78 | <p> | |
79 | With Local Functions (GCC only) | |
80 | </p> | |
81 | </th> | |
82 | <th> | |
83 | <p> | |
84 | C++11 Lambdas | |
85 | </p> | |
86 | </th> | |
87 | </tr></thead> | |
88 | <tbody><tr> | |
89 | <td> | |
90 | <p> | |
91 | </p> | |
92 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">val</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> | |
93 | <span class="keyword">int</span> <span class="identifier">nums</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span> | |
94 | <span class="keyword">int</span><span class="special">*</span> <span class="identifier">end</span> <span class="special">=</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">3</span><span class="special">;</span> | |
95 | ||
96 | <span class="keyword">int</span><span class="special">*</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">find_if</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">end</span><span class="special">,</span> | |
97 | <span class="identifier">GCC_LAMBDA</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">val</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">,</span> <span class="keyword">return</span> <span class="keyword">bool</span><span class="special">)</span> <span class="special">{</span> | |
98 | <span class="keyword">return</span> <span class="identifier">num</span> <span class="special">==</span> <span class="identifier">val</span><span class="special">;</span> | |
99 | <span class="special">}</span> <span class="identifier">GCC_LAMBDA_END</span> | |
100 | <span class="special">);</span> | |
101 | </pre> | |
102 | <p> | |
103 | </p> | |
104 | </td> | |
105 | <td> | |
106 | <p> | |
107 | </p> | |
108 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">val</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> | |
109 | <span class="keyword">int</span> <span class="identifier">nums</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span><span class="number">1</span><span class="special">,</span> <span class="number">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span> | |
110 | <span class="keyword">int</span><span class="special">*</span> <span class="identifier">end</span> <span class="special">=</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">3</span><span class="special">;</span> | |
111 | ||
112 | <span class="keyword">int</span><span class="special">*</span> <span class="identifier">iter</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">find_if</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">end</span><span class="special">,</span> | |
113 | <span class="special">[</span><span class="identifier">val</span><span class="special">](</span><span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">-></span> <span class="keyword">bool</span> <span class="special">{</span> | |
114 | <span class="keyword">return</span> <span class="identifier">num</span> <span class="special">==</span> <span class="identifier">val</span><span class="special">;</span> | |
115 | <span class="special">}</span> | |
116 | <span class="special">);</span> | |
117 | </pre> | |
118 | <p> | |
119 | </p> | |
120 | </td> | |
121 | </tr></tbody> | |
122 | </table></div> | |
123 | <p> | |
124 | The GCC lambda function macros are implemented using local functions (see | |
125 | also <a href="../../../example/gcc_lambda.hpp" target="_top"><code class="literal">gcc_lambda.hpp</code></a>): | |
126 | </p> | |
127 | <p> | |
128 | </p> | |
129 | <pre class="programlisting"><span class="preprocessor"># define</span> <span class="identifier">GCC_LAMBDA_</span><span class="special">(</span><span class="identifier">binds</span><span class="special">,</span> <span class="identifier">params</span><span class="special">,</span> <span class="identifier">results</span><span class="special">)</span> <span class="special">\</span> | |
130 | <span class="special">({</span> <span class="comment">/* open statement expression (GCC extension only) */</span> <span class="special">\</span> | |
131 | <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> <span class="special">\</span> | |
132 | <span class="identifier">BOOST_PP_LIST_ENUM</span><span class="special">(</span><span class="identifier">BOOST_PP_LIST_APPEND</span><span class="special">(</span><span class="identifier">binds</span><span class="special">,</span> <span class="special">\</span> | |
133 | <span class="identifier">BOOST_PP_LIST_APPEND</span><span class="special">(</span><span class="identifier">params</span><span class="special">,</span> <span class="special">\</span> | |
134 | <span class="identifier">BOOST_PP_IIF</span><span class="special">(</span><span class="identifier">BOOST_PP_LIST_IS_NIL</span><span class="special">(</span><span class="identifier">results</span><span class="special">),</span> <span class="special">\</span> | |
135 | <span class="special">(</span><span class="keyword">return</span> <span class="keyword">void</span><span class="special">,</span> <span class="identifier">BOOST_PP_NIL</span><span class="special">)</span> <span class="comment">/* default for lambdas */</span> <span class="special">\</span> | |
136 | <span class="special">,</span> <span class="special">\</span> | |
137 | <span class="identifier">results</span> <span class="special">\</span> | |
138 | <span class="special">)\</span> | |
139 | <span class="special">)</span> <span class="special">\</span> | |
140 | <span class="special">))</span> <span class="special">\</span> | |
141 | <span class="special">)</span> | |
142 | </pre> | |
143 | <p> | |
144 | </p> | |
145 | <p> | |
146 | </p> | |
147 | <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">GCC_LAMBDA_END_</span><span class="special">(</span><span class="identifier">id</span><span class="special">)</span> <span class="special">\</span> | |
148 | <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">gcc_lambda_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">))</span> <span class="special">\</span> | |
149 | <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">gcc_lambda_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">);</span> <span class="special">\</span> | |
150 | <span class="special">})</span> <span class="comment">/* close statement expression (GCC extension only) */</span> | |
151 | </pre> | |
152 | <p> | |
153 | </p> | |
154 | <p> | |
155 | This is possible because GCC statement expressions allow to use declaration | |
156 | statements within expressions and therefore to declare a local function within | |
157 | an expression. The macros automatically detect if the compiler supports | |
158 | <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
159 | lambda functions</a> in which case the implementation uses native lambdas | |
160 | instead of local functions in GCC statement expressions. However, <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
161 | lambda functions</a> do not support constant binding so it is best to | |
162 | only use <code class="computeroutput"><span class="keyword">const</span> <span class="identifier">bind</span> | |
163 | <span class="identifier">variable</span></code> (same as <code class="computeroutput"><span class="special">=</span><span class="identifier">variable</span></code> | |
164 | for <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
165 | lambda functions</a>) and <code class="computeroutput"><span class="identifier">bind</span><span class="special">&</span> <span class="identifier">variable</span></code> | |
166 | (same as <code class="computeroutput"><span class="special">&</span><span class="identifier">variable</span></code> | |
167 | for <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
168 | lambda functions</a>') because these have the exact same semantic between | |
169 | the local function and the native lambda implementations. Furthermore, local | |
170 | functions allow to bind data members directly while <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
171 | lambda functions</a> require to access data members via binding the object | |
172 | <code class="computeroutput"><span class="keyword">this</span></code>. Unfortunately, the short-hand | |
173 | binds <code class="computeroutput"><span class="special">&</span></code> and <code class="computeroutput"><span class="special">=</span></code> of <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
174 | lambda functions</a> (which automatically bind all variables in scope | |
175 | either by reference or value) are not supported by these GCC lambda function | |
176 | macros because they are not supported by local functions. Finally, the result | |
177 | type <code class="computeroutput"><span class="keyword">return</span> </code><code class="literal"><span class="emphasis"><em>result-type</em></span></code> | |
178 | is optional and it is assumed <code class="computeroutput"><span class="keyword">void</span></code> | |
179 | when it is not specified (same as with <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
180 | lambda functions</a>). | |
181 | </p> | |
182 | </div> | |
183 | <div class="section"> | |
184 | <div class="titlepage"><div><div><h3 class="title"> | |
185 | <a name="boost_localfunction.examples.constant_blocks"></a><a class="link" href="examples.html#boost_localfunction.examples.constant_blocks" title="Constant Blocks">Constant | |
186 | Blocks</a> | |
187 | </h3></div></div></div> | |
188 | <p> | |
189 | It is possible to use local functions to check assertions between variables | |
190 | that are made constant within the asserted expressions. This is advantageous | |
191 | because assertions are not supposed to change the state of the program and | |
192 | ideally the compiler will not compile assertions that modify variables. | |
193 | </p> | |
194 | <p> | |
195 | For example, consider the following assertion where by mistake we programmed | |
196 | <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span></code> | |
197 | instead of <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code>: | |
198 | </p> | |
199 | <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">y</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> | |
200 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">);</span> <span class="comment">// Mistakenly `=` instead of `==`.</span> | |
201 | </pre> | |
202 | <p> | |
203 | Ideally this code will not compile instead this example not only compiles | |
204 | but the assertion even passes the run-time check and no error is generated | |
205 | at all. The <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2004/n1613.pdf" target="_top">[N1613]</a> | |
206 | paper introduces the concept of a <span class="emphasis"><em>const-block</em></span> which | |
207 | could be used to wrap the assertion above and catch the programming error | |
208 | at compile-time. Similarly, the following code will generate a compile-time | |
209 | error when <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span></code> | |
210 | is mistakenly used instead of <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> because both <code class="computeroutput"><span class="identifier">x</span></code> | |
211 | and <code class="computeroutput"><span class="identifier">y</span></code> are made constants | |
212 | (using local functions) within the block of code performing the assertion | |
213 | (see also <a href="../../../example/const_block_error.cpp" target="_top"><code class="literal">const_block_error.cpp</code></a>): | |
214 | </p> | |
215 | <div class="informaltable"><table class="table"> | |
216 | <colgroup> | |
217 | <col> | |
218 | <col> | |
219 | </colgroup> | |
220 | <thead><tr> | |
221 | <th> | |
222 | <p> | |
223 | With Local Functions | |
224 | </p> | |
225 | </th> | |
226 | <th> | |
227 | <p> | |
228 | N1613 Const-Blocks | |
229 | </p> | |
230 | </th> | |
231 | </tr></thead> | |
232 | <tbody><tr> | |
233 | <td> | |
234 | <p> | |
235 | </p> | |
236 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">y</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> | |
237 | <span class="identifier">CONST_BLOCK</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">y</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Constant block.</span> | |
238 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">);</span> <span class="comment">// Compiler error.</span> | |
239 | <span class="special">}</span> <span class="identifier">CONST_BLOCK_END</span> | |
240 | </pre> | |
241 | <p> | |
242 | </p> | |
243 | </td> | |
244 | <td> | |
245 | <p> | |
246 | </p> | |
247 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">y</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> | |
248 | <span class="keyword">const</span> <span class="special">{</span> <span class="comment">// Constant block.</span> | |
249 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">);</span> <span class="comment">// Compiler error.</span> | |
250 | <span class="special">}</span> | |
251 | </pre> | |
252 | <p> | |
253 | </p> | |
254 | </td> | |
255 | </tr></tbody> | |
256 | </table></div> | |
257 | <p> | |
258 | The constant block macros are implemented using local functions (see also | |
259 | <a href="../../../example/const_block.hpp" target="_top"><code class="literal">const_block.hpp</code></a>): | |
260 | </p> | |
261 | <p> | |
262 | </p> | |
263 | <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">CONST_BLOCK_</span><span class="special">(</span><span class="identifier">variables</span><span class="special">)</span> <span class="special">\</span> | |
264 | <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> <span class="special">\</span> | |
265 | <span class="identifier">BOOST_PP_IIF</span><span class="special">(</span><span class="identifier">BOOST_PP_LIST_IS_NIL</span><span class="special">(</span><span class="identifier">variables</span><span class="special">),</span> <span class="special">\</span> | |
266 | <span class="keyword">void</span> <span class="identifier">BOOST_PP_TUPLE_EAT</span><span class="special">(</span><span class="number">3</span><span class="special">)</span> <span class="special">\</span> | |
267 | <span class="special">,</span> <span class="special">\</span> | |
268 | <span class="identifier">BOOST_PP_LIST_FOR_EACH_I</span> <span class="special">\</span> | |
269 | <span class="special">)(</span><span class="identifier">CONST_BLOCK_BIND_</span><span class="special">,</span> <span class="special">~,</span> <span class="identifier">variables</span><span class="special">)</span> <span class="special">\</span> | |
270 | <span class="special">)</span> | |
271 | </pre> | |
272 | <p> | |
273 | </p> | |
274 | <p> | |
275 | </p> | |
276 | <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">CONST_BLOCK_END_</span><span class="special">(</span><span class="identifier">id</span><span class="special">)</span> <span class="special">\</span> | |
277 | <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">const_block_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">))</span> <span class="special">\</span> | |
278 | <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">const_block_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">)();</span> <span class="comment">/* call local function immediately */</span> | |
279 | </pre> | |
280 | <p> | |
281 | </p> | |
282 | <p> | |
283 | The constant block macros are implemented using a local function which binds | |
284 | by constant reference <code class="computeroutput"><span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&</span></code> | |
285 | all the specified variables (so the variables are constant within the code | |
286 | block but they do not need to be <code class="computeroutput"><span class="identifier">CopyConstructible</span></code> | |
287 | and no extra copy is performed). The local function executes the <code class="computeroutput"><span class="identifier">assert</span></code> instruction in its body and it is | |
288 | called immediately after it is defined. More in general, constant blocks | |
289 | can be used to evaluate any instruction (not just assertions) within a block | |
290 | were all specified variables are constant. | |
291 | </p> | |
292 | <p> | |
293 | Unfortunately, constant blocks cannot be implemented with <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
294 | lambda functions</a> because these do not support constant binding. Variables | |
295 | bound by value using <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
296 | lambda functions</a> (<code class="computeroutput"><span class="identifier">variable</span></code>, | |
297 | <code class="computeroutput"><span class="special">=</span><span class="identifier">variable</span></code>, | |
298 | and <code class="computeroutput"><span class="special">=</span></code>) are constant but they | |
299 | are required to be <code class="computeroutput"><span class="identifier">CopyConstructible</span></code> | |
300 | and they introduce potentially expensive copy operations. <a href="#ftn.boost_localfunction.examples.constant_blocks.f0" class="footnote" name="boost_localfunction.examples.constant_blocks.f0"><sup class="footnote">[29]</sup></a> Of course it is always possible to introduce extra constant variables | |
301 | and bind these variables to the <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
302 | lambda functions</a> but the constant block code will then have to manage | |
303 | the declaration and initialization of these extra variables plus it will | |
304 | have to use the extra variable names instead of the original variable names: | |
305 | </p> | |
306 | <p> | |
307 | </p> | |
308 | <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">y</span> <span class="special">=</span> <span class="number">2</span><span class="special">;</span> | |
309 | <span class="keyword">const</span> <span class="keyword">decltype</span><span class="special">(</span><span class="identifier">x</span><span class="special">)&</span> <span class="identifier">const_x</span> <span class="special">=</span> <span class="identifier">x</span><span class="special">;</span> <span class="comment">// Constant so cannot be modified</span> | |
310 | <span class="keyword">const</span> <span class="keyword">decltype</span><span class="special">(</span><span class="identifier">y</span><span class="special">)&</span> <span class="identifier">const_y</span> <span class="special">=</span> <span class="identifier">y</span><span class="special">;</span> <span class="comment">// and reference so no copy.</span> | |
311 | <span class="special">[&</span><span class="identifier">const_x</span><span class="special">,</span> <span class="special">&</span><span class="identifier">const_y</span><span class="special">]()</span> <span class="special">{</span> <span class="comment">// Lambda functions (C++11 only).</span> | |
312 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">const_x</span> <span class="special">=</span> <span class="identifier">const_y</span><span class="special">);</span> <span class="comment">// Unfortunately, `const_` names.</span> | |
313 | <span class="special">}();</span> | |
314 | </pre> | |
315 | <p> | |
316 | </p> | |
317 | <p> | |
318 | In many cases the use of an extra constant variable <code class="computeroutput"><span class="identifier">const_x</span></code> | |
319 | can be acceptable but in other cases it might be preferable to maintain the | |
320 | same variable name <code class="computeroutput"><span class="identifier">x</span></code> within | |
321 | the function body. | |
322 | </p> | |
323 | </div> | |
324 | <div class="section"> | |
325 | <div class="titlepage"><div><div><h3 class="title"> | |
326 | <a name="boost_localfunction.examples.scope_exits"></a><a class="link" href="examples.html#boost_localfunction.examples.scope_exits" title="Scope Exits">Scope Exits</a> | |
327 | </h3></div></div></div> | |
328 | <p> | |
329 | Scope exits allow to execute arbitrary code at the exit of the enclosing | |
330 | scope and they are provided by the <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a> | |
331 | library. | |
332 | </p> | |
333 | <p> | |
334 | For curiosity, here we show how to re-implement scope exits using local functions. | |
335 | One small advantage of scope exits that use local functions is that they | |
336 | support constant binding. <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a> | |
337 | does not directly support constant binding (however, it is always possible | |
338 | to introduce an extra <code class="computeroutput"><span class="keyword">const</span></code> | |
339 | local variable, assign it to the value to bind, and then bind the <code class="computeroutput"><span class="keyword">const</span></code> variable so to effectively have constant | |
340 | binding with <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a> | |
341 | as well). | |
342 | </p> | |
343 | <div class="note"><table border="0" summary="Note"> | |
344 | <tr> | |
345 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> | |
346 | <th align="left">Note</th> | |
347 | </tr> | |
348 | <tr><td align="left" valign="top"><p> | |
349 | In general, the authors recommend to use <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a> | |
350 | instead of the code listed by this example whenever possible (because | |
351 | <a href="http://www.boost.org/libs/scope_exit" target="_top">Boost.ScopeExit</a> | |
352 | is a library deliberately designed to support the scope exit construct). | |
353 | </p></td></tr> | |
354 | </table></div> | |
355 | <p> | |
356 | The following example binds <code class="computeroutput"><span class="identifier">p</span></code> | |
357 | by constant reference so this variable cannot be modified within the scope | |
358 | exit body but it is not copied and it will present the value it has at the | |
359 | exit of the enclosing scope and not at the scope exit declaration (see also | |
360 | <a href="../../../example/scope_exit.cpp" target="_top"><code class="literal">scope_exit.cpp</code></a>): | |
361 | </p> | |
362 | <div class="informaltable"><table class="table"> | |
363 | <colgroup> | |
364 | <col> | |
365 | <col> | |
366 | </colgroup> | |
367 | <thead><tr> | |
368 | <th> | |
369 | <p> | |
370 | With Local Functions | |
371 | </p> | |
372 | </th> | |
373 | <th> | |
374 | <p> | |
375 | Boost.ScopeExit | |
376 | </p> | |
377 | </th> | |
378 | </tr></thead> | |
379 | <tbody><tr> | |
380 | <td> | |
381 | <p> | |
382 | </p> | |
383 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">person</span><span class="special">&</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">back</span><span class="special">();</span> | |
384 | <span class="identifier">person</span><span class="special">::</span><span class="identifier">evolution_t</span> <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution_</span><span class="special">;</span> | |
385 | ||
386 | <span class="identifier">SCOPE_EXIT</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">checkpoint</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">p</span><span class="special">,</span> <span class="identifier">bind</span> <span class="identifier">this_</span><span class="special">)</span> <span class="special">{</span> | |
387 | <span class="keyword">if</span> <span class="special">(</span><span class="identifier">checkpoint</span> <span class="special">==</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution_</span><span class="special">)</span> <span class="identifier">this_</span><span class="special">-></span><span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span> | |
388 | <span class="special">}</span> <span class="identifier">SCOPE_EXIT_END</span> | |
389 | </pre> | |
390 | <p> | |
391 | </p> | |
392 | </td> | |
393 | <td> | |
394 | <p> | |
395 | </p> | |
396 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">person</span><span class="special">&</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">persons_</span><span class="special">.</span><span class="identifier">back</span><span class="special">();</span> | |
397 | <span class="identifier">person</span><span class="special">::</span><span class="identifier">evolution_t</span> <span class="identifier">checkpoint</span> <span class="special">=</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution_</span><span class="special">;</span> | |
398 | ||
399 | <span class="identifier">BOOST_SCOPE_EXIT</span><span class="special">(</span><span class="identifier">checkpoint</span><span class="special">,</span> <span class="special">&</span><span class="identifier">p</span><span class="special">,</span> <span class="identifier">this_</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Or extra variable `const_p`.</span> | |
400 | <span class="keyword">if</span> <span class="special">(</span><span class="identifier">checkpoint</span> <span class="special">==</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">evolution_</span><span class="special">)</span> <span class="identifier">this_</span><span class="special">-></span><span class="identifier">persons_</span><span class="special">.</span><span class="identifier">pop_back</span><span class="special">();</span> | |
401 | <span class="special">}</span> <span class="identifier">BOOST_SCOPE_EXIT_END</span> | |
402 | </pre> | |
403 | <p> | |
404 | </p> | |
405 | </td> | |
406 | </tr></tbody> | |
407 | </table></div> | |
408 | <p> | |
409 | The scope exit macros are implemented by passing a local function when constructing | |
410 | an object of the following class (see also <a href="../../../example/scope_exit.hpp" target="_top"><code class="literal">scope_exit.hpp</code></a>): | |
411 | </p> | |
412 | <p> | |
413 | </p> | |
414 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">scope_exit</span> <span class="special">{</span> | |
415 | <span class="identifier">scope_exit</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">void</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)></span> <span class="identifier">f</span><span class="special">):</span> <span class="identifier">f_</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> <span class="special">{}</span> | |
416 | <span class="special">~</span><span class="identifier">scope_exit</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">f_</span><span class="special">();</span> <span class="special">}</span> | |
417 | <span class="keyword">private</span><span class="special">:</span> | |
418 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">void</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)></span> <span class="identifier">f_</span><span class="special">;</span> | |
419 | <span class="special">};</span> | |
420 | </pre> | |
421 | <p> | |
422 | </p> | |
423 | <p> | |
424 | </p> | |
425 | <pre class="programlisting"><span class="preprocessor"># define</span> <span class="identifier">SCOPE_EXIT</span><span class="special">(...)</span> <span class="special">\</span> | |
426 | <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="identifier">__VA_ARGS__</span><span class="special">)</span> | |
427 | </pre> | |
428 | <p> | |
429 | </p> | |
430 | <p> | |
431 | </p> | |
432 | <pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">SCOPE_EXIT_END_</span><span class="special">(</span><span class="identifier">id</span><span class="special">)</span> <span class="special">\</span> | |
433 | <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">scope_exit_func_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">))</span> <span class="special">\</span> | |
434 | <span class="identifier">scope_exit</span> <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">scope_exit_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">)(</span> <span class="special">\</span> | |
435 | <span class="identifier">BOOST_PP_CAT</span><span class="special">(</span><span class="identifier">scope_exit_func_</span><span class="special">,</span> <span class="identifier">id</span><span class="special">));</span> | |
436 | </pre> | |
437 | <p> | |
438 | </p> | |
439 | <p> | |
440 | A local variable within the enclosing scope is used to hold the object so | |
441 | the destructor will be invoked at the exit of the enclosing scope and it | |
442 | will in turn call the local function executing the scope exit instructions. | |
443 | The scope exit local function has no parameter and <code class="computeroutput"><span class="keyword">void</span></code> | |
444 | result type but it supports binding and constant binding. | |
445 | </p> | |
446 | </div> | |
447 | <div class="section"> | |
448 | <div class="titlepage"><div><div><h3 class="title"> | |
449 | <a name="boost_localfunction.examples.boost_phoenix_functions"></a><a class="link" href="examples.html#boost_localfunction.examples.boost_phoenix_functions" title="Boost.Phoenix Functions">Boost.Phoenix | |
450 | Functions</a> | |
451 | </h3></div></div></div> | |
452 | <p> | |
453 | Local functions can be used to create <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> | |
454 | functions. For example (see also <a href="../../../example/phoenix_factorial_local.cpp" target="_top"><code class="literal">phoenix_factorial_local.cpp</code></a> | |
455 | and <a href="../../../example/phoenix_factorial.cpp" target="_top"><code class="literal">phoenix_factorial.cpp</code></a>): | |
456 | </p> | |
457 | <div class="informaltable"><table class="table"> | |
458 | <colgroup> | |
459 | <col> | |
460 | <col> | |
461 | </colgroup> | |
462 | <thead><tr> | |
463 | <th> | |
464 | <p> | |
465 | Local Functions | |
466 | </p> | |
467 | </th> | |
468 | <th> | |
469 | <p> | |
470 | Global Functor | |
471 | </p> | |
472 | </th> | |
473 | </tr></thead> | |
474 | <tbody><tr> | |
475 | <td> | |
476 | <p> | |
477 | </p> | |
478 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> | |
479 | <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">arg_names</span><span class="special">::</span><span class="identifier">arg1</span><span class="special">;</span> | |
480 | ||
481 | <span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">n</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Unfortunately, monomorphic.</span> | |
482 | <span class="keyword">return</span> <span class="special">(</span><span class="identifier">n</span> <span class="special"><=</span> <span class="number">0</span><span class="special">)</span> <span class="special">?</span> <span class="number">1</span> <span class="special">:</span> <span class="identifier">n</span> <span class="special">*</span> <span class="identifier">factorial_impl</span><span class="special">(</span><span class="identifier">n</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span> | |
483 | <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">recursive</span> <span class="identifier">factorial_impl</span><span class="special">)</span> | |
484 | ||
485 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(</span><span class="keyword">int</span><span class="special">)></span> <span class="special">></span> | |
486 | <span class="identifier">factorial</span><span class="special">(</span><span class="identifier">factorial_impl</span><span class="special">);</span> <span class="comment">// Phoenix function from local function.</span> | |
487 | ||
488 | <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">4</span><span class="special">;</span> | |
489 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">factorial</span><span class="special">(</span><span class="identifier">i</span><span class="special">)()</span> <span class="special">==</span> <span class="number">24</span><span class="special">);</span> <span class="comment">// Call.</span> | |
490 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">factorial</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">)(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">==</span> <span class="number">24</span><span class="special">);</span> <span class="comment">// Lazy call.</span> | |
491 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
492 | <span class="special">}</span> | |
493 | </pre> | |
494 | <p> | |
495 | </p> | |
496 | </td> | |
497 | <td> | |
498 | <p> | |
499 | </p> | |
500 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">struct</span> <span class="identifier">factorial_impl</span> <span class="special">{</span> <span class="comment">// Phoenix function from global functor.</span> | |
501 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">></span> | |
502 | <span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span> | |
503 | ||
504 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">This</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">></span> | |
505 | <span class="keyword">struct</span> <span class="identifier">result</span><span class="special"><</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span><span class="special">)></span> <span class="special">:</span> <span class="identifier">result</span><span class="special"><</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span> <span class="keyword">const</span><span class="special">&)></span> <span class="special">{};</span> | |
506 | ||
507 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">This</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">></span> | |
508 | <span class="keyword">struct</span> <span class="identifier">result</span><span class="special"><</span><span class="identifier">This</span> <span class="special">(</span><span class="identifier">Arg</span><span class="special">&)></span> <span class="special">{</span> <span class="keyword">typedef</span> <span class="identifier">Arg</span> <span class="identifier">type</span><span class="special">;</span> <span class="special">};</span> | |
509 | ||
510 | <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Arg</span><span class="special">></span> <span class="comment">// Polymorphic.</span> | |
511 | <span class="identifier">Arg</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Arg</span> <span class="identifier">n</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">{</span> | |
512 | <span class="keyword">return</span> <span class="special">(</span><span class="identifier">n</span> <span class="special"><=</span> <span class="number">0</span><span class="special">)</span> <span class="special">?</span> <span class="number">1</span> <span class="special">:</span> <span class="identifier">n</span> <span class="special">*</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)(</span><span class="identifier">n</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span> | |
513 | <span class="special">}</span> | |
514 | <span class="special">};</span> | |
515 | ||
516 | <span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> | |
517 | <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">arg_names</span><span class="special">::</span><span class="identifier">arg1</span><span class="special">;</span> | |
518 | ||
519 | <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">function</span><span class="special"><</span><span class="identifier">factorial_impl</span><span class="special">></span> <span class="identifier">factorial</span><span class="special">;</span> | |
520 | ||
521 | <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">4</span><span class="special">;</span> | |
522 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">factorial</span><span class="special">(</span><span class="identifier">i</span><span class="special">)()</span> <span class="special">==</span> <span class="number">24</span><span class="special">);</span> <span class="comment">// Call.</span> | |
523 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">factorial</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">)(</span><span class="identifier">i</span><span class="special">)</span> <span class="special">==</span> <span class="number">24</span><span class="special">);</span> <span class="comment">// Lazy call.</span> | |
524 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
525 | <span class="special">}</span> | |
526 | </pre> | |
527 | <p> | |
528 | </p> | |
529 | </td> | |
530 | </tr></tbody> | |
531 | </table></div> | |
532 | <p> | |
533 | This is presented here mainly as a curiosity because <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> | |
534 | functions created from local functions have the important limitation that | |
535 | they cannot be polymorphic. <a href="#ftn.boost_localfunction.examples.boost_phoenix_functions.f0" class="footnote" name="boost_localfunction.examples.boost_phoenix_functions.f0"><sup class="footnote">[30]</sup></a> Therefore, in many cases creating the <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> | |
536 | function from global functors (possibly with the help of <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> | |
537 | adaptor macros) might be a more useful. | |
538 | </p> | |
539 | </div> | |
540 | <div class="section"> | |
541 | <div class="titlepage"><div><div><h3 class="title"> | |
542 | <a name="boost_localfunction.examples.closures"></a><a class="link" href="examples.html#boost_localfunction.examples.closures" title="Closures">Closures</a> | |
543 | </h3></div></div></div> | |
544 | <p> | |
545 | The following are examples of <a href="http://en.wikipedia.org/wiki/Closure_(computer_science)" target="_top">closures</a> | |
546 | that illustrate how to return local functions to the calling scope (note | |
547 | how extra care is taken in order to ensure that all bound variables remain | |
548 | valid at the calling scope): | |
549 | </p> | |
550 | <div class="informaltable"><table class="table"> | |
551 | <colgroup><col></colgroup> | |
552 | <thead><tr><th> | |
553 | <p> | |
554 | Files | |
555 | </p> | |
556 | </th></tr></thead> | |
557 | <tbody> | |
558 | <tr><td> | |
559 | <p> | |
560 | <a href="../../../test/return_inc.cpp" target="_top"><code class="literal">return_inc.cpp</code></a> | |
561 | </p> | |
562 | </td></tr> | |
563 | <tr><td> | |
564 | <p> | |
565 | <a href="../../../test/return_this.cpp" target="_top"><code class="literal">return_this.cpp</code></a> | |
566 | </p> | |
567 | </td></tr> | |
568 | <tr><td> | |
569 | <p> | |
570 | <a href="../../../test/return_setget.cpp" target="_top"><code class="literal">return_setget.cpp</code></a> | |
571 | </p> | |
572 | </td></tr> | |
573 | <tr><td> | |
574 | <p> | |
575 | <a href="../../../test/return_derivative.cpp" target="_top"><code class="literal">return_derivative.cpp</code></a> | |
576 | </p> | |
577 | </td></tr> | |
578 | </tbody> | |
579 | </table></div> | |
580 | </div> | |
581 | <div class="section"> | |
582 | <div class="titlepage"><div><div><h3 class="title"> | |
583 | <a name="boost_localfunction.examples.gcc_nested_functions"></a><a class="link" href="examples.html#boost_localfunction.examples.gcc_nested_functions" title="GCC Nested Functions">GCC | |
584 | Nested Functions</a> | |
585 | </h3></div></div></div> | |
586 | <p> | |
587 | The GCC C compiler supports local functions as a non-standard extension under | |
588 | the name of <a href="http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html" target="_top">nested | |
589 | functions</a>. Note that nested functions are exclusively a C extension | |
590 | of the GCC compiler (they are not supported for C++ not even by the GCC compiler, | |
591 | and they are not part of any C or C++ standard, nor they are supported by | |
592 | other compilers like MSVC). | |
593 | </p> | |
594 | <p> | |
595 | The following examples are taken form the GCC nested function documentation | |
596 | and programmed using local functions: | |
597 | </p> | |
598 | <div class="informaltable"><table class="table"> | |
599 | <colgroup><col></colgroup> | |
600 | <thead><tr><th> | |
601 | <p> | |
602 | Files | |
603 | </p> | |
604 | </th></tr></thead> | |
605 | <tbody> | |
606 | <tr><td> | |
607 | <p> | |
608 | <a href="../../../example/gcc_square.cpp" target="_top"><code class="literal">gcc_square.cpp</code></a> | |
609 | </p> | |
610 | </td></tr> | |
611 | <tr><td> | |
612 | <p> | |
613 | <a href="../../../example/gcc_access.cpp" target="_top"><code class="literal">gcc_access.cpp</code></a> | |
614 | </p> | |
615 | </td></tr> | |
616 | <tr><td> | |
617 | <p> | |
618 | <a href="../../../example/gcc_store.cpp" target="_top"><code class="literal">gcc_store.cpp</code></a> | |
619 | </p> | |
620 | </td></tr> | |
621 | </tbody> | |
622 | </table></div> | |
623 | </div> | |
624 | <div class="section"> | |
625 | <div class="titlepage"><div><div><h3 class="title"> | |
626 | <a name="boost_localfunction.examples.n_papers"></a><a class="link" href="examples.html#boost_localfunction.examples.n_papers" title="N-Papers">N-Papers</a> | |
627 | </h3></div></div></div> | |
628 | <p> | |
629 | The following examples are taken from different C++ "N-papers" | |
630 | and programmed using local functions: | |
631 | </p> | |
632 | <div class="informaltable"><table class="table"> | |
633 | <colgroup> | |
634 | <col> | |
635 | <col> | |
636 | </colgroup> | |
637 | <thead><tr> | |
638 | <th> | |
639 | <p> | |
640 | Files | |
641 | </p> | |
642 | </th> | |
643 | <th> | |
644 | <p> | |
645 | Notes | |
646 | </p> | |
647 | </th> | |
648 | </tr></thead> | |
649 | <tbody> | |
650 | <tr> | |
651 | <td> | |
652 | <p> | |
653 | <a href="../../../example/n2550_find_if.cpp" target="_top"><code class="literal">n2550_find_if.cpp</code></a> | |
654 | </p> | |
655 | </td> | |
656 | <td> | |
657 | <p> | |
658 | This example is adapted from <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2550.pdf" target="_top">[N2550]</a> | |
659 | (<a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
660 | lambda functions</a>): It passes a local function to the STL | |
661 | algorithm <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">find_if</span></code>. | |
662 | </p> | |
663 | </td> | |
664 | </tr> | |
665 | <tr> | |
666 | <td> | |
667 | <p> | |
668 | <a href="../../../example/n2529_this.cpp" target="_top"><code class="literal">n2529_this.cpp</code></a> | |
669 | </p> | |
670 | </td> | |
671 | <td> | |
672 | <p> | |
673 | This example is adapted from <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2529.pdf" target="_top">[N2529]</a> | |
674 | (<a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
675 | lambda functions</a>): It binds the object in scope <code class="computeroutput"><span class="keyword">this</span></code> to a local function. | |
676 | </p> | |
677 | </td> | |
678 | </tr> | |
679 | </tbody> | |
680 | </table></div> | |
681 | </div> | |
682 | <div class="footnotes"> | |
683 | <br><hr style="width:100; text-align:left;margin-left: 0"> | |
684 | <div id="ftn.boost_localfunction.examples.constant_blocks.f0" class="footnote"><p><a href="#boost_localfunction.examples.constant_blocks.f0" class="para"><sup class="para">[29] </sup></a> | |
685 | Ideally, <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
686 | lambda functions</a> would allow to bind variables also using <code class="computeroutput"><span class="keyword">const</span><span class="special">&</span> <span class="identifier">variable</span></code> (constant reference) and <code class="computeroutput"><span class="keyword">const</span><span class="special">&</span></code> | |
687 | (all variables by constant reference). | |
688 | </p></div> | |
689 | <div id="ftn.boost_localfunction.examples.boost_phoenix_functions.f0" class="footnote"><p><a href="#boost_localfunction.examples.boost_phoenix_functions.f0" class="para"><sup class="para">[30] </sup></a> | |
690 | <span class="bold"><strong>Rationale.</strong></span> Local functions can only be | |
691 | monomorphic because they are implemented using local classes and local | |
692 | classes cannot be templates in C++ (not even in <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a>). | |
693 | </p></div> | |
694 | </div> | |
695 | </div> | |
696 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
697 | <td align="left"></td> | |
698 | <td align="right"><div class="copyright-footer">Copyright © 2009-2012 Lorenzo | |
699 | Caminiti<p> | |
700 | Distributed under the Boost Software License, Version 1.0 (see accompanying | |
701 | file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) | |
702 | </p> | |
703 | </div></td> | |
704 | </tr></table> | |
705 | <hr> | |
706 | <div class="spirit-nav"> | |
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