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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.alternatives"></a><a class="link" href="alternatives.html" title="Annex: Alternatives">Annex: Alternatives</a> | |
28 | </h2></div></div></div> | |
29 | <p> | |
30 | This section compares the features offered by this library with similar features | |
31 | offered by C++ and by other libraries. | |
32 | </p> | |
33 | <h4> | |
34 | <a name="boost_localfunction.alternatives.h0"></a> | |
35 | <span class="phrase"><a name="boost_localfunction.alternatives.features"></a></span><a class="link" href="alternatives.html#boost_localfunction.alternatives.features">Features</a> | |
36 | </h4> | |
37 | <p> | |
38 | The following table compares local function features. | |
39 | </p> | |
40 | <div class="informaltable"><table class="table"> | |
41 | <colgroup> | |
42 | <col> | |
43 | <col> | |
44 | <col> | |
45 | <col> | |
46 | <col> | |
47 | <col> | |
48 | </colgroup> | |
49 | <thead><tr> | |
50 | <th> | |
51 | <p> | |
52 | Local Function Feature | |
53 | </p> | |
54 | </th> | |
55 | <th> | |
56 | <p> | |
57 | Boost.LocalFunction | |
58 | </p> | |
59 | </th> | |
60 | <th> | |
61 | <p> | |
62 | C++11 Lambda Function (Not C++03) | |
63 | </p> | |
64 | </th> | |
65 | <th> | |
66 | <p> | |
67 | Local Functor | |
68 | </p> | |
69 | </th> | |
70 | <th> | |
71 | <p> | |
72 | Global Functor (Not Local) | |
73 | </p> | |
74 | </th> | |
75 | <th> | |
76 | <p> | |
77 | Boost.Phoenix | |
78 | </p> | |
79 | </th> | |
80 | </tr></thead> | |
81 | <tbody> | |
82 | <tr> | |
83 | <td> | |
84 | <p> | |
85 | <span class="emphasis"><em>Can be defined locally</em></span> | |
86 | </p> | |
87 | </td> | |
88 | <td> | |
89 | <p> | |
90 | Yes. | |
91 | </p> | |
92 | </td> | |
93 | <td> | |
94 | <p> | |
95 | Yes. | |
96 | </p> | |
97 | </td> | |
98 | <td> | |
99 | <p> | |
100 | Yes. | |
101 | </p> | |
102 | </td> | |
103 | <td> | |
104 | <p> | |
105 | No. Therefore this not really an alternative implementation of local | |
106 | functions but it is listed here just for comparison. | |
107 | </p> | |
108 | </td> | |
109 | <td> | |
110 | <p> | |
111 | Yes. | |
112 | </p> | |
113 | </td> | |
114 | </tr> | |
115 | <tr> | |
116 | <td> | |
117 | <p> | |
118 | <span class="emphasis"><em>Can be defined using C++ statement syntax</em></span> | |
119 | </p> | |
120 | </td> | |
121 | <td> | |
122 | <p> | |
123 | Yes. Plus eventual compiler errors and debugging retain their usual | |
124 | meaning and format. | |
125 | </p> | |
126 | </td> | |
127 | <td> | |
128 | <p> | |
129 | Yes. Plus eventual compiler errors and debugging retain their usual | |
130 | meaning and format. | |
131 | </p> | |
132 | </td> | |
133 | <td> | |
134 | <p> | |
135 | Yes. Plus eventual compiler errors and debugging retain their usual | |
136 | meaning and format. | |
137 | </p> | |
138 | </td> | |
139 | <td> | |
140 | <p> | |
141 | Yes. Plus eventual compiler errors and debugging retain their usual | |
142 | meaning and format. | |
143 | </p> | |
144 | </td> | |
145 | <td> | |
146 | <p> | |
147 | No (it uses C++ <a href="http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Expression-template" target="_top">expression | |
148 | template</a> syntax). | |
149 | </p> | |
150 | </td> | |
151 | </tr> | |
152 | <tr> | |
153 | <td> | |
154 | <p> | |
155 | <span class="emphasis"><em>Can be defined within expressions</em></span> | |
156 | </p> | |
157 | </td> | |
158 | <td> | |
159 | <p> | |
160 | No. It can be defined only within declarations. | |
161 | </p> | |
162 | </td> | |
163 | <td> | |
164 | <p> | |
165 | Yes (plus the local function can be unnamed). | |
166 | </p> | |
167 | </td> | |
168 | <td> | |
169 | <p> | |
170 | No. It can be defined only within declarations. | |
171 | </p> | |
172 | </td> | |
173 | <td> | |
174 | <p> | |
175 | No. It can be defined only within declarations. | |
176 | </p> | |
177 | </td> | |
178 | <td> | |
179 | <p> | |
180 | Yes (plus the local function can be unnamed). | |
181 | </p> | |
182 | </td> | |
183 | </tr> | |
184 | <tr> | |
185 | <td> | |
186 | <p> | |
187 | <span class="emphasis"><em>Can be passed as template parameter (e.g., to STL algorithms)</em></span> | |
188 | </p> | |
189 | </td> | |
190 | <td> | |
191 | <p> | |
192 | Yes. The <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> | |
193 | standard does not allow to pass local types as template parameters | |
194 | (see <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm" target="_top">[N2657]</a>) | |
195 | but this library implements a "trick" to get around this | |
196 | limitation (see the <a class="link" href="implementation.html" title="Annex: Implementation">Implementation</a> | |
197 | section). | |
198 | </p> | |
199 | </td> | |
200 | <td> | |
201 | <p> | |
202 | Yes. | |
203 | </p> | |
204 | </td> | |
205 | <td> | |
206 | <p> | |
207 | No on <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> | |
208 | compilers (but yes on <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
209 | compilers and some compilers like MSVC 8.0, see <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm" target="_top">[N2657]</a>). | |
210 | </p> | |
211 | </td> | |
212 | <td> | |
213 | <p> | |
214 | Yes. | |
215 | </p> | |
216 | </td> | |
217 | <td> | |
218 | <p> | |
219 | Yes. | |
220 | </p> | |
221 | </td> | |
222 | </tr> | |
223 | <tr> | |
224 | <td> | |
225 | <p> | |
226 | <span class="emphasis"><em>Access variables in scope</em></span> | |
227 | </p> | |
228 | </td> | |
229 | <td> | |
230 | <p> | |
231 | Yes. The variable names are repeated in the function declaration | |
232 | so they can be bound by value, by constant value, by reference, and | |
233 | by constant reference (the object <code class="computeroutput"><span class="keyword">this</span></code> | |
234 | can also be bound using <code class="computeroutput"><span class="identifier">this_</span></code>). | |
235 | </p> | |
236 | </td> | |
237 | <td> | |
238 | <p> | |
239 | Yes. The variable names are repeated in the function declaration | |
240 | (plus there is a short-hand syntax to bind all variables in scope | |
241 | at once) so they can be bound by constant value and by reference | |
242 | (the object <code class="computeroutput"><span class="keyword">this</span></code> can | |
243 | also be bound). However, variables cannot be bound by constant references | |
244 | (see below). | |
245 | </p> | |
246 | </td> | |
247 | <td> | |
248 | <p> | |
249 | No. Programmers must manually program functor data members and explicitly | |
250 | specify their types to access variables in scope. | |
251 | </p> | |
252 | </td> | |
253 | <td> | |
254 | <p> | |
255 | No. Programmers must manually program functor data members and explicitly | |
256 | specify their types to access variables in scope. | |
257 | </p> | |
258 | </td> | |
259 | <td> | |
260 | <p> | |
261 | Yes. Variables in scope are accessible as usual within expressions | |
262 | (plus <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">let</span></code> can be used to bind variables | |
263 | by constant reference). | |
264 | </p> | |
265 | </td> | |
266 | </tr> | |
267 | <tr> | |
268 | <td> | |
269 | <p> | |
270 | <span class="emphasis"><em><a href="http://en.wikipedia.org/wiki/Type_polymorphism#Parametric_polymorphism" target="_top">Polymorphic</a> | |
271 | in the function parameter type</em></span> | |
272 | </p> | |
273 | </td> | |
274 | <td> | |
275 | <p> | |
276 | No (local functions cannot be function templates). | |
277 | </p> | |
278 | </td> | |
279 | <td> | |
280 | <p> | |
281 | No (<a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
282 | lambdas cannot be function templates). | |
283 | </p> | |
284 | </td> | |
285 | <td> | |
286 | <p> | |
287 | No (local classes cannot have member function templates). | |
288 | </p> | |
289 | </td> | |
290 | <td> | |
291 | <p> | |
292 | Yes. | |
293 | </p> | |
294 | </td> | |
295 | <td> | |
296 | <p> | |
297 | Yes. | |
298 | </p> | |
299 | </td> | |
300 | </tr> | |
301 | </tbody> | |
302 | </table></div> | |
303 | <p> | |
304 | <span class="bold"><strong>C++11 Lambda Function</strong></span> | |
305 | </p> | |
306 | <p> | |
307 | <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
308 | lambda functions</a> have most of the features of this library plus some | |
309 | additional feature (see also the example in the <a class="link" href="../index.html#boost_localfunction.introduction" title="Introduction">Introduction</a> | |
310 | section): | |
311 | </p> | |
312 | <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> | |
313 | <li class="listitem"> | |
314 | <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
315 | lambda functions</a> can be defined within expressions while this library | |
316 | local functions can only be defined at declaration scope. | |
317 | </li> | |
318 | <li class="listitem"> | |
319 | <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
320 | lambda functions</a> are only supported by the <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
321 | standard so they are not supported by all C++ compilers. This library local | |
322 | functions can be programmed also on <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> | |
323 | compilers (and they have performances comparable to <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
324 | lambda functions</a> on <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
325 | compilers). | |
326 | </li> | |
327 | <li class="listitem"> | |
328 | <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
329 | lambda functions</a> do not allow to bind variables in scope by constant | |
330 | reference. Because a variable cannot be bound by constant reference, <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
331 | lambda functions</a> can bind a variable by constant only if the variable | |
332 | is <code class="computeroutput"><span class="identifier">CopyConstructible</span></code> and | |
333 | the binding requires a (potentially expensive) extra copy operation. Constant | |
334 | reference binding is instead supported by this library. | |
335 | </li> | |
336 | <li class="listitem"> | |
337 | <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
338 | lambda functions</a> do not allow to bind data members selectively | |
339 | without binding also the object <code class="computeroutput"><span class="keyword">this</span></code> | |
340 | while this library local functions can bind either selected data members | |
341 | or the entire object <code class="computeroutput"><span class="keyword">this</span></code> | |
342 | (using <code class="computeroutput"><span class="identifier">this_</span></code>). | |
343 | </li> | |
344 | <li class="listitem"> | |
345 | <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
346 | lambda functions</a> provide a short-hand syntax to bind all variables | |
347 | in scope at once (<code class="computeroutput"><span class="special">&</span></code> or | |
348 | <code class="computeroutput"><span class="special">=</span></code>) while this library local | |
349 | function always require to bind variables naming them one-by-one. | |
350 | </li> | |
351 | </ul></div> | |
352 | <p> | |
353 | For example, for non-copyable objects (see also <a href="../../../example/noncopyable_cxx11_lambda_error.cpp" target="_top"><code class="literal">noncopyable_cxx11_lambda_error.cpp</code></a> | |
354 | and <a href="../../../example/noncopyable_local_function.cpp" target="_top"><code class="literal">noncopyable_local_function.cpp</code></a>): | |
355 | </p> | |
356 | <div class="informaltable"><table class="table"> | |
357 | <colgroup> | |
358 | <col> | |
359 | <col> | |
360 | </colgroup> | |
361 | <thead><tr> | |
362 | <th> | |
363 | <p> | |
364 | C++11 Lambda Function | |
365 | </p> | |
366 | </th> | |
367 | <th> | |
368 | <p> | |
369 | Boost.LocalFunction | |
370 | </p> | |
371 | </th> | |
372 | </tr></thead> | |
373 | <tbody><tr> | |
374 | <td> | |
375 | <p> | |
376 | </p> | |
377 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">struct</span> <span class="identifier">n</span><span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">noncopyable</span> <span class="special">{</span> | |
378 | <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span> | |
379 | <span class="identifier">n</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">_i</span><span class="special">):</span> <span class="identifier">i</span><span class="special">(</span><span class="identifier">_i</span><span class="special">)</span> <span class="special">{}</span> | |
380 | <span class="special">};</span> | |
381 | ||
382 | ||
383 | <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> | |
384 | <span class="identifier">n</span> <span class="identifier">x</span><span class="special">(-</span><span class="number">1</span><span class="special">);</span> | |
385 | ||
386 | <span class="keyword">auto</span> <span class="identifier">f</span> <span class="special">=</span> <span class="special">[</span><span class="identifier">x</span><span class="special">](</span><span class="keyword">void</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Error: x is non-copyable, but if</span> | |
387 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">i</span> <span class="special">==</span> <span class="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// bind `&x` then `x` is not constant.</span> | |
388 | <span class="special">};</span> | |
389 | <span class="identifier">f</span><span class="special">();</span> | |
390 | ||
391 | <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> | |
392 | <span class="special">}</span> | |
393 | </pre> | |
394 | <p> | |
395 | </p> | |
396 | </td> | |
397 | <td> | |
398 | <p> | |
399 | </p> | |
400 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">struct</span> <span class="identifier">n</span><span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">noncopyable</span> <span class="special">{</span> | |
401 | <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span> | |
402 | <span class="identifier">n</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">_i</span><span class="special">):</span> <span class="identifier">i</span><span class="special">(</span><span class="identifier">_i</span><span class="special">)</span> <span class="special">{}</span> | |
403 | <span class="special">};</span> | |
404 | <span class="identifier">BOOST_TYPEOF_REGISTER_TYPE</span><span class="special">(</span><span class="identifier">n</span><span class="special">)</span> <span class="comment">// Register for `bind& x` below.</span> | |
405 | ||
406 | <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> | |
407 | <span class="identifier">n</span> <span class="identifier">x</span><span class="special">(-</span><span class="number">1</span><span class="special">);</span> | |
408 | ||
409 | <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// OK: No copy</span> | |
410 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">i</span> <span class="special">==</span> <span class="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// and constant.</span> | |
411 | <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> | |
412 | <span class="identifier">f</span><span class="special">();</span> | |
413 | ||
414 | <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> | |
415 | <span class="special">}</span> | |
416 | </pre> | |
417 | <p> | |
418 | </p> | |
419 | </td> | |
420 | </tr></tbody> | |
421 | </table></div> | |
422 | <p> | |
423 | Or, for objects with expensive copy operations (see also <a href="../../../example/expensive_copy_cxx11_lambda.cpp" target="_top"><code class="literal">expensive_copy_cxx11_lambda.cpp</code></a> | |
424 | and <a href="../../../example/expensive_copy_local_function.cpp" target="_top"><code class="literal">expensive_copy_local_function.cpp</code></a>): | |
425 | </p> | |
426 | <div class="informaltable"><table class="table"> | |
427 | <colgroup> | |
428 | <col> | |
429 | <col> | |
430 | </colgroup> | |
431 | <thead><tr> | |
432 | <th> | |
433 | <p> | |
434 | C++11 Lambda Function | |
435 | </p> | |
436 | </th> | |
437 | <th> | |
438 | <p> | |
439 | Boost.LocalFunction | |
440 | </p> | |
441 | </th> | |
442 | </tr></thead> | |
443 | <tbody><tr> | |
444 | <td> | |
445 | <p> | |
446 | </p> | |
447 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">struct</span> <span class="identifier">n</span> <span class="special">{</span> | |
448 | <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span> | |
449 | <span class="identifier">n</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">_i</span><span class="special">):</span> <span class="identifier">i</span><span class="special">(</span><span class="identifier">_i</span><span class="special">)</span> <span class="special">{}</span> | |
450 | <span class="identifier">n</span><span class="special">(</span><span class="identifier">n</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">):</span> <span class="identifier">i</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">i</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Some time consuming copy operation.</span> | |
451 | <span class="keyword">for</span> <span class="special">(</span><span class="keyword">unsigned</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">10000</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="char">'.'</span><span class="special">;</span> | |
452 | <span class="special">}</span> | |
453 | <span class="special">};</span> | |
454 | ||
455 | ||
456 | <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> | |
457 | <span class="identifier">n</span> <span class="identifier">x</span><span class="special">(-</span><span class="number">1</span><span class="special">);</span> | |
458 | ||
459 | <span class="keyword">auto</span> <span class="identifier">f</span> <span class="special">=</span> <span class="special">[</span><span class="identifier">x</span><span class="special">]()</span> <span class="special">{</span> <span class="comment">// Problem: Expensive copy, but if bind</span> | |
460 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">i</span> <span class="special">==</span> <span class="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// by `&x` then `x` is not constant.</span> | |
461 | <span class="special">};</span> | |
462 | <span class="identifier">f</span><span class="special">();</span> | |
463 | ||
464 | <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> | |
465 | <span class="special">}</span> | |
466 | </pre> | |
467 | <p> | |
468 | </p> | |
469 | </td> | |
470 | <td> | |
471 | <p> | |
472 | </p> | |
473 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">struct</span> <span class="identifier">n</span> <span class="special">{</span> | |
474 | <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span> | |
475 | <span class="identifier">n</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">_i</span><span class="special">):</span> <span class="identifier">i</span><span class="special">(</span><span class="identifier">_i</span><span class="special">)</span> <span class="special">{}</span> | |
476 | <span class="identifier">n</span><span class="special">(</span><span class="identifier">n</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">):</span> <span class="identifier">i</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">i</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// Some time consuming copy operation.</span> | |
477 | <span class="keyword">for</span> <span class="special">(</span><span class="keyword">unsigned</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">10000</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="char">'.'</span><span class="special">;</span> | |
478 | <span class="special">}</span> | |
479 | <span class="special">};</span> | |
480 | <span class="identifier">BOOST_TYPEOF_REGISTER_TYPE</span><span class="special">(</span><span class="identifier">n</span><span class="special">)</span> <span class="comment">// Register for `bind& x` below.</span> | |
481 | ||
482 | <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> | |
483 | <span class="identifier">n</span> <span class="identifier">x</span><span class="special">(-</span><span class="number">1</span><span class="special">);</span> | |
484 | ||
485 | <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">{</span> <span class="comment">// OK: No copy expensive</span> | |
486 | <span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">i</span> <span class="special">==</span> <span class="special">-</span><span class="number">1</span><span class="special">);</span> <span class="comment">// copy but constant.</span> | |
487 | <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">f</span><span class="special">)</span> | |
488 | <span class="identifier">f</span><span class="special">();</span> | |
489 | ||
490 | <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> | |
491 | <span class="special">}</span> | |
492 | </pre> | |
493 | <p> | |
494 | </p> | |
495 | </td> | |
496 | </tr></tbody> | |
497 | </table></div> | |
498 | <p> | |
499 | When constant binding functionality is needed for <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
500 | lambda functions</a>, the best alternative might be to bind an extra local | |
501 | variable declared constant and initialized to the original variable (for example, | |
502 | see <span class="emphasis"><em>constant blocks</em></span> implemented with <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
503 | lambda functions</a> in the <a class="link" href="examples.html" title="Examples">Examples</a> | |
504 | section). | |
505 | </p> | |
506 | <p> | |
507 | <span class="bold"><strong>Local Functor</strong></span> | |
508 | </p> | |
509 | <p> | |
510 | The following example compares local functions with C++ local functors (see | |
511 | also <a href="../../../example/add_local_functor.cpp" target="_top"><code class="literal">add_local_functor.cpp</code></a> | |
512 | and <a href="../../../test/add.cpp" target="_top"><code class="literal">add.cpp</code></a>): | |
513 | </p> | |
514 | <div class="informaltable"><table class="table"> | |
515 | <colgroup> | |
516 | <col> | |
517 | <col> | |
518 | </colgroup> | |
519 | <thead><tr> | |
520 | <th> | |
521 | <p> | |
522 | Local Functor | |
523 | </p> | |
524 | </th> | |
525 | <th> | |
526 | <p> | |
527 | Boost.LocalFunction | |
528 | </p> | |
529 | </th> | |
530 | </tr></thead> | |
531 | <tbody><tr> | |
532 | <td> | |
533 | <p> | |
534 | </p> | |
535 | <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> | |
536 | <span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> | |
537 | ||
538 | <span class="keyword">struct</span> <span class="identifier">local_add</span> <span class="special">{</span> <span class="comment">// Unfortunately, boilerplate code to program the class.</span> | |
539 | <span class="identifier">local_add</span><span class="special">(</span><span class="keyword">int</span><span class="special">&</span> <span class="identifier">_sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">_factor</span><span class="special">):</span> <span class="identifier">sum</span><span class="special">(</span><span class="identifier">_sum</span><span class="special">),</span> <span class="identifier">factor</span><span class="special">(</span><span class="identifier">_factor</span><span class="special">)</span> <span class="special">{}</span> | |
540 | ||
541 | <span class="keyword">inline</span> <span class="keyword">void</span> <span class="keyword">operator</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="comment">// Body uses C++ statement syntax.</span> | |
542 | <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> | |
543 | <span class="special">}</span> | |
544 | ||
545 | <span class="keyword">private</span><span class="special">:</span> <span class="comment">// Unfortunately, cannot bind so repeat variable types.</span> | |
546 | <span class="keyword">int</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">;</span> <span class="comment">// Access `sum` by reference.</span> | |
547 | <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">factor</span><span class="special">;</span> <span class="comment">// Make `factor` constant.</span> | |
548 | <span class="special">}</span> <span class="identifier">add</span><span class="special">(</span><span class="identifier">sum</span><span class="special">,</span> <span class="identifier">factor</span><span class="special">);</span> | |
549 | ||
550 | <span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> | |
551 | <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">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span> | |
552 | <span class="comment">// Unfortunately, cannot pass as template parameter to `std::for_each`.</span> | |
553 | <span class="keyword">for</span><span class="special">(</span><span class="identifier">size_t</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">2</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="identifier">add</span><span class="special">(</span><span class="identifier">nums</span><span class="special">[</span><span class="identifier">i</span><span class="special">]);</span> | |
554 | ||
555 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span> | |
556 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
557 | <span class="special">}</span> | |
558 | </pre> | |
559 | <p> | |
560 | </p> | |
561 | </td> | |
562 | <td> | |
563 | <p> | |
564 | </p> | |
565 | <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> <span class="comment">// Some local scope.</span> | |
566 | <span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> <span class="comment">// Variables in scope to bind.</span> | |
567 | ||
568 | <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">{</span> | |
569 | <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> | |
570 | <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> | |
571 | ||
572 | <span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Call the local function.</span> | |
573 | <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">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span> | |
574 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">add</span><span class="special">);</span> <span class="comment">// Pass it to an algorithm.</span> | |
575 | ||
576 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span> <span class="comment">// Assert final summation value.</span> | |
577 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
578 | <span class="special">}</span> | |
579 | </pre> | |
580 | <p> | |
581 | </p> | |
582 | </td> | |
583 | </tr></tbody> | |
584 | </table></div> | |
585 | <p> | |
586 | <span class="bold"><strong>Global Functor</strong></span> | |
587 | </p> | |
588 | <p> | |
589 | The following example compares local functions with C++ global functors (see | |
590 | also <a href="../../../example/add_global_functor.cpp" target="_top"><code class="literal">add_global_functor.cpp</code></a> | |
591 | and <a href="../../../test/add.cpp" target="_top"><code class="literal">add.cpp</code></a>): | |
592 | </p> | |
593 | <div class="informaltable"><table class="table"> | |
594 | <colgroup> | |
595 | <col> | |
596 | <col> | |
597 | </colgroup> | |
598 | <thead><tr> | |
599 | <th> | |
600 | <p> | |
601 | Global Functor | |
602 | </p> | |
603 | </th> | |
604 | <th> | |
605 | <p> | |
606 | Boost.LocalFunction | |
607 | </p> | |
608 | </th> | |
609 | </tr></thead> | |
610 | <tbody><tr> | |
611 | <td> | |
612 | <p> | |
613 | </p> | |
614 | <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="comment">// Unfortunately, cannot be defined locally (so not a real alternative).</span> | |
615 | <span class="keyword">struct</span> <span class="identifier">global_add</span> <span class="special">{</span> <span class="comment">// Unfortunately, boilerplate code to program the class.</span> | |
616 | <span class="identifier">global_add</span><span class="special">(</span><span class="keyword">int</span><span class="special">&</span> <span class="identifier">_sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">_factor</span><span class="special">):</span> <span class="identifier">sum</span><span class="special">(</span><span class="identifier">_sum</span><span class="special">),</span> <span class="identifier">factor</span><span class="special">(</span><span class="identifier">_factor</span><span class="special">)</span> <span class="special">{}</span> | |
617 | ||
618 | <span class="keyword">inline</span> <span class="keyword">void</span> <span class="keyword">operator</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="comment">// Body uses C++ statement syntax.</span> | |
619 | <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> | |
620 | <span class="special">}</span> | |
621 | ||
622 | <span class="keyword">private</span><span class="special">:</span> <span class="comment">// Unfortunately, cannot bind so repeat variable types.</span> | |
623 | <span class="keyword">int</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">;</span> <span class="comment">// Access `sum` by reference.</span> | |
624 | <span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">factor</span><span class="special">;</span> <span class="comment">// Make `factor` constant.</span> | |
625 | <span class="special">};</span> | |
626 | ||
627 | <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> | |
628 | <span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> | |
629 | ||
630 | <span class="identifier">global_add</span> <span class="identifier">add</span><span class="special">(</span><span class="identifier">sum</span><span class="special">,</span> <span class="identifier">factor</span><span class="special">);</span> | |
631 | ||
632 | <span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> | |
633 | <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">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span> | |
634 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">add</span><span class="special">);</span> <span class="comment">// Passed as template parameter.</span> | |
635 | ||
636 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span> | |
637 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
638 | <span class="special">}</span> | |
639 | </pre> | |
640 | <p> | |
641 | </p> | |
642 | </td> | |
643 | <td> | |
644 | <p> | |
645 | </p> | |
646 | <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> <span class="comment">// Some local scope.</span> | |
647 | <span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> <span class="comment">// Variables in scope to bind.</span> | |
648 | ||
649 | <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">{</span> | |
650 | <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> | |
651 | <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> | |
652 | ||
653 | <span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Call the local function.</span> | |
654 | <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">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span> | |
655 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">add</span><span class="special">);</span> <span class="comment">// Pass it to an algorithm.</span> | |
656 | ||
657 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span> <span class="comment">// Assert final summation value.</span> | |
658 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
659 | <span class="special">}</span> | |
660 | </pre> | |
661 | <p> | |
662 | </p> | |
663 | </td> | |
664 | </tr></tbody> | |
665 | </table></div> | |
666 | <p> | |
667 | However, note that global functors do not allow to define the function locally | |
668 | so they are not a real alternative implementation of local functions. | |
669 | </p> | |
670 | <p> | |
671 | <span class="bold"><strong>Boost.Phoenix</strong></span> | |
672 | </p> | |
673 | <p> | |
674 | The following example compares local functions with <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> | |
675 | (see also <a href="../../../example/add_phoenix.cpp" target="_top"><code class="literal">add_phoenix.cpp</code></a> | |
676 | and <a href="../../../test/add.cpp" target="_top"><code class="literal">add.cpp</code></a>): | |
677 | </p> | |
678 | <div class="informaltable"><table class="table"> | |
679 | <colgroup> | |
680 | <col> | |
681 | <col> | |
682 | </colgroup> | |
683 | <thead><tr> | |
684 | <th> | |
685 | <p> | |
686 | Boost.Phoenix | |
687 | </p> | |
688 | </th> | |
689 | <th> | |
690 | <p> | |
691 | Boost.LocalFunction | |
692 | </p> | |
693 | </th> | |
694 | </tr></thead> | |
695 | <tbody><tr> | |
696 | <td> | |
697 | <p> | |
698 | </p> | |
699 | <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> | |
700 | <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">let</span><span class="special">;</span> | |
701 | <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">local_names</span><span class="special">::</span><span class="identifier">_f</span><span class="special">;</span> | |
702 | <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">cref</span><span class="special">;</span> | |
703 | <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">ref</span><span class="special">;</span> | |
704 | <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">_1</span><span class="special">;</span> | |
705 | ||
706 | <span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> | |
707 | <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> | |
708 | ||
709 | <span class="comment">// Passed to template, `factor` by constant, and defined in expression.</span> | |
710 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">3</span><span class="special">,</span> <span class="identifier">let</span><span class="special">(</span><span class="identifier">_f</span> <span class="special">=</span> <span class="identifier">cref</span><span class="special">(</span><span class="identifier">factor</span><span class="special">))[</span> | |
711 | <span class="comment">// Unfortunately, body cannot use C++ statement syntax.</span> | |
712 | <span class="identifier">ref</span><span class="special">(</span><span class="identifier">sum</span><span class="special">)</span> <span class="special">+=</span> <span class="identifier">_f</span> <span class="special">*</span> <span class="identifier">_1</span><span class="special">,</span> <span class="identifier">_1</span> <span class="comment">// Access `sum` by reference.</span> | |
713 | <span class="special">]);</span> | |
714 | ||
715 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span> | |
716 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
717 | <span class="special">}</span> | |
718 | </pre> | |
719 | <p> | |
720 | </p> | |
721 | </td> | |
722 | <td> | |
723 | <p> | |
724 | </p> | |
725 | <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> <span class="comment">// Some local scope.</span> | |
726 | <span class="keyword">int</span> <span class="identifier">sum</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span> <span class="number">10</span><span class="special">;</span> <span class="comment">// Variables in scope to bind.</span> | |
727 | ||
728 | <span class="keyword">void</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">bind</span> <span class="identifier">factor</span><span class="special">,</span> <span class="identifier">bind</span><span class="special">&</span> <span class="identifier">sum</span><span class="special">,</span> <span class="keyword">int</span> <span class="identifier">num</span><span class="special">)</span> <span class="special">{</span> | |
729 | <span class="identifier">sum</span> <span class="special">+=</span> <span class="identifier">factor</span> <span class="special">*</span> <span class="identifier">num</span><span class="special">;</span> | |
730 | <span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span> | |
731 | ||
732 | <span class="identifier">add</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> <span class="comment">// Call the local function.</span> | |
733 | <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">2</span><span class="special">,</span> <span class="number">3</span><span class="special">};</span> | |
734 | <span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">nums</span><span class="special">,</span> <span class="identifier">nums</span> <span class="special">+</span> <span class="number">2</span><span class="special">,</span> <span class="identifier">add</span><span class="special">);</span> <span class="comment">// Pass it to an algorithm.</span> | |
735 | ||
736 | <span class="identifier">BOOST_TEST</span><span class="special">(</span><span class="identifier">sum</span> <span class="special">==</span> <span class="number">60</span><span class="special">);</span> <span class="comment">// Assert final summation value.</span> | |
737 | <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">report_errors</span><span class="special">();</span> | |
738 | <span class="special">}</span> | |
739 | </pre> | |
740 | <p> | |
741 | </p> | |
742 | </td> | |
743 | </tr></tbody> | |
744 | </table></div> | |
745 | <p> | |
746 | The comparison in this section does not include the <a href="http://www.boost.org/libs/lambda" target="_top">Boost.Lambda</a> | |
747 | library because that library is obsolete and it was replaced by <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a>. | |
748 | The <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> library | |
749 | version 3.0 is used for this comparison. | |
750 | </p> | |
751 | <h4> | |
752 | <a name="boost_localfunction.alternatives.h1"></a> | |
753 | <span class="phrase"><a name="boost_localfunction.alternatives.performances"></a></span><a class="link" href="alternatives.html#boost_localfunction.alternatives.performances">Performances</a> | |
754 | </h4> | |
755 | <p> | |
756 | The following tables compare run-times, compile-times, and binary sizes for | |
757 | the different alternatives to local functions presented in this section. | |
758 | </p> | |
759 | <p> | |
760 | Overall, this library has compile-times and generates binary sizes similar | |
761 | to the ones of the other approaches. This library run-times on <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> | |
762 | compilers were measured to be larger than other approaches when compiler optimization | |
763 | is enabled (using <code class="computeroutput"><span class="identifier">bjam</span> <span class="identifier">release</span> | |
764 | <span class="special">...</span></code>). However, on compilers that allow | |
765 | to pass local types as template parameters (e.g., MSVC 8.0 or GCC 4.5.3 with | |
766 | <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> features | |
767 | enabled <code class="literal">-std=c++0x</code>, see also <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm" target="_top">[N2657]</a> | |
768 | and <a href="http://www.boost.org/libs/chrono" target="_top">Boost.Config</a>'s <code class="computeroutput"><span class="identifier">BOOST_NO_CXX11_LOCAL_CLASS_TEMPLATE_PARAMETERS</span></code>) | |
769 | this library automatically generates optimized code that runs as fast as the | |
770 | fastest of the other approaches (see the "Boost.LocalFunction" approach | |
771 | below). When this library local function is specified <code class="computeroutput"><span class="keyword">inline</span></code> | |
772 | (see the "Boost.LocalFunction Inline" approach below and the <a class="link" href="advanced_topics.html" title="Advanced Topics">Advanced Topics</a> section) | |
773 | its run-times are always comparable to both the "Local Functor" and | |
774 | "Global Functor" approaches. However, in these cases the local function | |
775 | cannot be portably passed as template parameter (see <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm" target="_top">[N2657]</a> | |
776 | and <a href="http://www.boost.org/libs/chrono" target="_top">Boost.Config</a>'s <code class="computeroutput"><span class="identifier">BOOST_NO_CXX11_LOCAL_CLASS_TEMPLATE_PARAMETERS</span></code>) | |
777 | so <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span></code> is replaced by a for-loop (on MSVC | |
778 | the for-loop, and not the local function in fact the same applies to local | |
779 | functors, was measured to have worst performances than using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span></code>). | |
780 | Finally, this library run-times are always among the fastest when no compiler | |
781 | optimization is enabled (using <code class="computeroutput"><span class="identifier">bjam</span> | |
782 | <span class="identifier">debug</span> <span class="special">...</span></code>). | |
783 | </p> | |
784 | <div class="note"><table border="0" summary="Note"> | |
785 | <tr> | |
786 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> | |
787 | <th align="left">Note</th> | |
788 | </tr> | |
789 | <tr><td align="left" valign="top"><p> | |
790 | The run-time performances of this library local functions are explained because | |
791 | on <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> | |
792 | compliant compilers (e.g., GCC 4.5.3 without <code class="literal">-std=c++0x</code>) | |
793 | this library needs to use a function pointer in order to portably pass the | |
794 | local function class as a template parameter (see <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2657.htm" target="_top">[N2657]</a> | |
795 | and the <a class="link" href="implementation.html" title="Annex: Implementation">Implementation</a> | |
796 | section). For all tested compilers, this function pointer prevents the compiler | |
797 | optimization algorithms from inlining the local function calls. Instead, | |
798 | the functors used by other approaches (e.g., <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a>) | |
799 | have been observed to allow all tested compilers to inline all the function | |
800 | calls for optimization. This run-time performance cost is not present on | |
801 | compilers that allow to pass local types as template parameters (e.g., MSVC | |
802 | 8.0 or GCC 4.5.3 with <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
803 | features enabled <code class="literal">-std=c++0x</code>, see <a href="http://www.boost.org/libs/chrono" target="_top">Boost.Config</a>'s | |
804 | <code class="computeroutput"><span class="identifier">BOOST_NO_CXX11_LOCAL_CLASS_TEMPLATE_PARAMETERS</span></code>) | |
805 | because this library does not have to use the extra function pointer to implement | |
806 | the local function call (it directly passes the local class type as template | |
807 | parameter). | |
808 | </p></td></tr> | |
809 | </table></div> | |
810 | <p> | |
811 | This run-time performance cost on <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> | |
812 | compilers might or might not be an issue depending on the performance requirements | |
813 | of specific applications. For example, an application might already be using | |
814 | a number of indirect function calls (function pointers, virtual functions, | |
815 | etc) for which the overhead added by using the one extra function pointer required | |
816 | by the local function call might not be noticeable within the overall program | |
817 | run-time. | |
818 | </p> | |
819 | <p> | |
820 | Finally, note that only a very simple local function body with just a single | |
821 | instruction was used for the anaylsis presented here (see the source files | |
822 | below). The authors have not studied how this library and the other approaches | |
823 | will perform with respect to each other when a more complex set of instructions | |
824 | is programmed for the local function body (e.g., <span class="emphasis"><em>if</em></span> a | |
825 | more complex set of instructions in the local function body were to inhibit | |
826 | some compiler from inlining function objects also other approaches like <a href="http://en.wikipedia.org/wiki/C%2B%2B0x#Lambda_functions_and_expressions" target="_top">C++11 | |
827 | lambda functions</a> and <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> | |
828 | <span class="emphasis"><em>could</em></span> start to show higher run-times even when optimization | |
829 | is enabled). | |
830 | </p> | |
831 | <p> | |
832 | The following commands were executed from the library example directory to | |
833 | measure compile-time, binary size, and run-time respectively: | |
834 | </p> | |
835 | <pre class="programlisting">> touch <FILE_NAME>.cpp # force recompilation | |
836 | > python chrono.py bjam {release|debug} <FILE_NAME> # compile-time | |
837 | > size <FILE_NAME> # binary size | |
838 | > ./<FILE_NAME> # run-time | |
839 | </pre> | |
840 | <p> | |
841 | The local function was called <code class="literal">1e8</code> times to add together | |
842 | all the elements of a vector and the run-time was measured using <a href="http://www.boost.org/libs/chrono" target="_top">Boost.Chrono</a> | |
843 | averaging over <code class="literal">10</code> executions of the vector summation (see | |
844 | the source files below). | |
845 | </p> | |
846 | <div class="informaltable"><table class="table"> | |
847 | <colgroup> | |
848 | <col> | |
849 | <col> | |
850 | <col> | |
851 | </colgroup> | |
852 | <thead><tr> | |
853 | <th> | |
854 | <p> | |
855 | Legend | |
856 | </p> | |
857 | </th> | |
858 | <th> | |
859 | <p> | |
860 | Approach | |
861 | </p> | |
862 | </th> | |
863 | <th> | |
864 | <p> | |
865 | Source File | |
866 | </p> | |
867 | </th> | |
868 | </tr></thead> | |
869 | <tbody> | |
870 | <tr> | |
871 | <td> | |
872 | <p> | |
873 | <span class="inlinemediaobject"><img src="../../../example/profile_legend_local_function.png" alt="profile_legend_local_function"></span> | |
874 | </p> | |
875 | </td> | |
876 | <td> | |
877 | <p> | |
878 | <a href="http://www.boost.org/libs/local_function" target="_top">Boost.LocalFunction</a> | |
879 | </p> | |
880 | </td> | |
881 | <td> | |
882 | <p> | |
883 | <a href="../../../example/profile_local_function.cpp" target="_top"><code class="literal">profile_local_function.cpp</code></a> | |
884 | </p> | |
885 | </td> | |
886 | </tr> | |
887 | <tr> | |
888 | <td> | |
889 | <p> | |
890 | <span class="inlinemediaobject"><img src="../../../example/profile_legend_local_function_inline.png" alt="profile_legend_local_function_inline"></span> | |
891 | </p> | |
892 | </td> | |
893 | <td> | |
894 | <p> | |
895 | <a href="http://www.boost.org/libs/local_function" target="_top">Boost.LocalFunction</a> | |
896 | inline | |
897 | </p> | |
898 | </td> | |
899 | <td> | |
900 | <p> | |
901 | <a href="../../../example/profile_local_function_inline.cpp" target="_top"><code class="literal">profile_local_function_inline.cpp</code></a> | |
902 | </p> | |
903 | </td> | |
904 | </tr> | |
905 | <tr> | |
906 | <td> | |
907 | <p> | |
908 | <span class="inlinemediaobject"><img src="../../../example/profile_legend_cxx11_lambda.png" alt="profile_legend_cxx11_lambda"></span> | |
909 | </p> | |
910 | </td> | |
911 | <td> | |
912 | <p> | |
913 | <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
914 | Lambda Function <a href="#ftn.boost_localfunction.alternatives.f0" class="footnote" name="boost_localfunction.alternatives.f0"><sup class="footnote">[a]</sup></a> | |
915 | </p> | |
916 | </td> | |
917 | <td> | |
918 | <p> | |
919 | <a href="../../../example/profile_cxx11_lambda.cpp" target="_top"><code class="literal">profile_cxx11_lambda.cpp</code></a> | |
920 | </p> | |
921 | </td> | |
922 | </tr> | |
923 | <tr> | |
924 | <td> | |
925 | <p> | |
926 | <span class="inlinemediaobject"><img src="../../../example/profile_legend_local_functor.png" alt="profile_legend_local_functor"></span> | |
927 | </p> | |
928 | </td> | |
929 | <td> | |
930 | <p> | |
931 | Local Functor | |
932 | </p> | |
933 | </td> | |
934 | <td> | |
935 | <p> | |
936 | <a href="../../../example/profile_local_functor.cpp" target="_top"><code class="literal">profile_local_functor.cpp</code></a> | |
937 | </p> | |
938 | </td> | |
939 | </tr> | |
940 | <tr> | |
941 | <td> | |
942 | <p> | |
943 | <span class="inlinemediaobject"><img src="../../../example/profile_legend_global_functor.png" alt="profile_legend_global_functor"></span> | |
944 | </p> | |
945 | </td> | |
946 | <td> | |
947 | <p> | |
948 | Global Functor | |
949 | </p> | |
950 | </td> | |
951 | <td> | |
952 | <p> | |
953 | <a href="../../../example/profile_global_functor.cpp" target="_top"><code class="literal">profile_global_functor.cpp</code></a> | |
954 | </p> | |
955 | </td> | |
956 | </tr> | |
957 | <tr> | |
958 | <td> | |
959 | <p> | |
960 | <span class="inlinemediaobject"><img src="../../../example/profile_legend_phoenix.png" alt="profile_legend_phoenix"></span> | |
961 | </p> | |
962 | </td> | |
963 | <td> | |
964 | <p> | |
965 | <a href="http://www.boost.org/libs/phoenix" target="_top">Boost.Phoenix</a> | |
966 | </p> | |
967 | </td> | |
968 | <td> | |
969 | <p> | |
970 | <a href="../../../example/profile_phoenix.cpp" target="_top"><code class="literal">profile_phoenix.cpp</code></a> | |
971 | </p> | |
972 | </td> | |
973 | </tr> | |
974 | </tbody> | |
975 | <tbody class="footnotes"><tr><td colspan="3"><div id="ftn.boost_localfunction.alternatives.f0" class="footnote"><p><a href="#boost_localfunction.alternatives.f0" class="para"><sup class="para">[a] </sup></a> | |
976 | Measurements available only for <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
977 | compilers. | |
978 | </p></div></td></tr></tbody> | |
979 | </table></div> | |
980 | <div class="informaltable"><table class="table"> | |
981 | <colgroup><col></colgroup> | |
982 | <thead><tr><th> | |
983 | <p> | |
984 | GCC 4.5.3 With C++11 Lambda Functions and "Local Classes as | |
985 | Template Parameters" (<code class="literal">bjam cxxflags=-std=c++0x ...</code>) | |
986 | </p> | |
987 | </th></tr></thead> | |
988 | <tbody> | |
989 | <tr><td> | |
990 | <p> | |
991 | <span class="bold"><strong>Compiled with <code class="literal">bjam release ...</code> | |
992 | for maximum optimization (<code class="literal">-O3 -finline-functions</code>)</strong></span> | |
993 | <span class="inlinemediaobject"><img src="../../../example/profile_gcc_cxx11_release.png" width="1170" alt="profile_gcc_cxx11_release"></span> | |
994 | </p> | |
995 | </td></tr> | |
996 | <tr><td> | |
997 | <p> | |
998 | <span class="bold"><strong>Compiled with <code class="literal">bjam debug ...</code> | |
999 | for no optimization (<code class="literal">-O0 -fno-inline</code>)</strong></span> | |
1000 | <span class="inlinemediaobject"><img src="../../../example/profile_gcc_cxx11_debug.png" width="1170" alt="profile_gcc_cxx11_debug"></span> | |
1001 | </p> | |
1002 | </td></tr> | |
1003 | </tbody> | |
1004 | </table></div> | |
1005 | <div class="informaltable"><table class="table"> | |
1006 | <colgroup><col></colgroup> | |
1007 | <thead><tr><th> | |
1008 | <p> | |
1009 | MSVC 8.0 With "Local Classes as Template Parameters" (Without | |
1010 | C++11 Lambda Functions) | |
1011 | </p> | |
1012 | </th></tr></thead> | |
1013 | <tbody> | |
1014 | <tr><td> | |
1015 | <p> | |
1016 | <span class="bold"><strong>Compiled with <code class="literal">bjam release ...</code> | |
1017 | for maximum optimization (<code class="literal">/O2 /Ob2</code>)</strong></span> | |
1018 | <span class="inlinemediaobject"><img src="../../../example/profile_msvc_release.png" width="1170" alt="profile_msvc_release"></span> | |
1019 | </p> | |
1020 | </td></tr> | |
1021 | <tr><td> | |
1022 | <p> | |
1023 | <span class="bold"><strong>Compiled with <code class="literal">bjam debug ...</code> | |
1024 | for no optimization (<code class="literal">/Od /Ob0</code>)</strong></span> <span class="inlinemediaobject"><img src="../../../example/profile_msvc_debug.png" width="1170" alt="profile_msvc_debug"></span> | |
1025 | </p> | |
1026 | </td></tr> | |
1027 | </tbody> | |
1028 | </table></div> | |
1029 | <div class="informaltable"><table class="table"> | |
1030 | <colgroup><col></colgroup> | |
1031 | <thead><tr><th> | |
1032 | <p> | |
1033 | GCC 4.3.4 With <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a> | |
1034 | Only (Without <a href="http://www.open-std.org/JTC1/SC22/WG21/" target="_top">C++11</a> | |
1035 | Lambda Functions and Without "Local Classes as Template Parameters") | |
1036 | </p> | |
1037 | </th></tr></thead> | |
1038 | <tbody> | |
1039 | <tr><td> | |
1040 | <p> | |
1041 | <span class="bold"><strong>Compiled with <code class="literal">bjam release ...</code> | |
1042 | for maximum optimization (<code class="literal">-O3 -finline-functions</code>)</strong></span> | |
1043 | <span class="inlinemediaobject"><img src="../../../example/profile_gcc_release.png" width="1170" alt="profile_gcc_release"></span> | |
1044 | </p> | |
1045 | </td></tr> | |
1046 | <tr><td> | |
1047 | <p> | |
1048 | <span class="bold"><strong>Compiled with <code class="literal">bjam debug ...</code> | |
1049 | for no optimization (<code class="literal">-O0 -fno-inline</code>)</strong></span> | |
1050 | <span class="inlinemediaobject"><img src="../../../example/profile_gcc_debug.png" width="1170" alt="profile_gcc_debug"></span> | |
1051 | </p> | |
1052 | </td></tr> | |
1053 | </tbody> | |
1054 | </table></div> | |
1055 | </div> | |
1056 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
1057 | <td align="left"></td> | |
1058 | <td align="right"><div class="copyright-footer">Copyright © 2009-2012 Lorenzo | |
1059 | Caminiti<p> | |
1060 | Distributed under the Boost Software License, Version 1.0 (see accompanying | |
1061 | 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>) | |
1062 | </p> | |
1063 | </div></td> | |
1064 | </tr></table> | |
1065 | <hr> | |
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