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288 | </head> | |
289 | <body> | |
290 | <div class="document" id="boost-pointer-container-library"> | |
291 | <h1 class="title"><img alt="Boost" src="boost.png" /> Pointer Container Library</h1> | |
292 | <h2 class="subtitle" id="indirected-functions">Indirected functions</h2> | |
293 | <p>It is quite common that we have two pointers and what to compare the | |
294 | pointed to objects. Also, we have usually already defined how | |
295 | to compare the objects. So to avoid some tedious boiler-plate code | |
296 | this library defines predicates that apply an indirection before comparing.</p> | |
297 | <p>When the container uses <tt class="docutils literal"><span class="pre">void*</span></tt> internally, we can use the | |
298 | class <tt class="docutils literal"><span class="pre">void_ptr_indirect_fun</span></tt>; otherwise we use the class | |
299 | <tt class="docutils literal"><span class="pre">indirect_fun</span></tt>.</p> | |
300 | <p><strong>Example:</strong></p> | |
301 | <pre class="literal-block"> | |
302 | std::string* bar = new std::string("bar"); | |
303 | std::string* foo = new std::string("foo"); | |
304 | BOOST_ASSERT( indirect_fun< std::less<std::string> >()( bar, foo ) == true ); | |
305 | BOOST_ASSERT( make_indirect_fun( std::less<std::string>() )( foo, bar ) == false ); | |
306 | ||
307 | void* vptr1 = ptr1; | |
308 | void* vptr2 = ptr2; | |
309 | void_ptr_indirect_fun< std::less<std::string>, std::string> cast_fun; | |
310 | BOOST_CHECK( cast_fun( vptr1, vptr2 ) == true ); | |
311 | </pre> | |
312 | <p><strong>See also:</strong></p> | |
313 | <ul class="simple"> | |
314 | <li><a class="reference" href="http://www.boost.org/libs/utility/utility.htm#result_of">result_of</a></li> | |
315 | <li><a class="reference" href="http://www.boost.org/libs/iterator/doc/pointee.html">pointee</a></li> | |
316 | <li><a class="reference" href="ptr_set.html">ptr_set</a></li> | |
317 | <li><a class="reference" href="ptr_multiset.html">ptr_multiset</a></li> | |
318 | </ul> | |
319 | <p><strong>Navigate</strong></p> | |
320 | <ul class="simple"> | |
321 | <li><a class="reference" href="ptr_container.html">home</a></li> | |
322 | <li><a class="reference" href="reference.html">reference</a></li> | |
323 | </ul> | |
324 | <p><strong>Remarks:</strong></p> | |
325 | <p>The class <tt class="docutils literal"><span class="pre">indirect_fun</span></tt> will work with smart pointers such as <a class="reference" href="http://www.boost.org/libs/smart_ptr/shared_ptr.htm">boost::shared_ptr<T></a> | |
326 | because of the type traits <tt class="docutils literal"><span class="pre">pointee<T>::type</span></tt> from the header <tt class="docutils literal"><span class="pre"><boost/pointee.hpp></span></tt>.</p> | |
327 | <p><strong>Synopsis:</strong></p> | |
328 | <p>Since the definition of the predicates is somewhat trivial, only the | |
329 | first operation is expanded inline.</p> | |
330 | <pre class="literal-block"> | |
331 | namespace boost | |
332 | { | |
333 | ||
334 | template< class Fun > | |
335 | struct indirect_fun | |
336 | { | |
337 | indirect_fun() : fun(Fun()) | |
338 | { } | |
339 | ||
340 | indirect_fun( Fun f ) : fun(f) | |
341 | { } | |
342 | ||
343 | template< class T > | |
344 | typename result_of< Fun( typename pointee<T>::type ) >::type | |
345 | operator()( const T& r ) const | |
346 | { | |
347 | return fun( *r ); | |
348 | } | |
349 | ||
350 | template< class T, class U > | |
351 | typename result_of< Fun( typename pointee<T>::type, | |
352 | typename pointee<U>::type ) >::type | |
353 | operator()( const T& r, const U& r2 ) const | |
354 | { | |
355 | return fun( *r, *r2 ); | |
356 | } | |
357 | ||
358 | private: | |
359 | Fun fun; | |
360 | }; | |
361 | ||
362 | template< class Fun > | |
363 | inline indirect_fun<Fun> make_indirect_fun( Fun f ) | |
364 | { | |
365 | return indirect_fun<Fun>( f ); | |
366 | } | |
367 | ||
368 | ||
369 | ||
370 | template< class Fun, class Arg1, class Arg2 = Arg1 > | |
371 | struct void_ptr_indirect_fun | |
372 | { | |
373 | void_ptr_indirect_fun() : fun(Fun()) | |
374 | { } | |
375 | ||
376 | void_ptr_indirect_fun( Fun f ) : fun(f) | |
377 | { } | |
378 | ||
379 | typename result_of< Fun( Arg1 ) >::type | |
380 | operator()( const void* r ) const | |
381 | { | |
382 | return fun( * static_cast<const Arg1*>( r ) ); | |
383 | } | |
384 | ||
385 | typename result_of< Fun( Arg1, Arg2 ) >::type | |
386 | operator()( const void* l, const void* r ) const | |
387 | { | |
388 | return fun( * static_cast<const Arg1*>( l ), * static_cast<const Arg2*>( r ) ); | |
389 | } | |
390 | ||
391 | private: | |
392 | Fun fun; | |
393 | }; | |
394 | ||
395 | template< class Fun, class Arg > | |
396 | inline void_ptr_indirect_fun<Fun,Arg> | |
397 | make_void_ptr_indirect_fun( Fun f ) | |
398 | { | |
399 | return void_ptr_indirect_fun<Fun,Arg>( f ); | |
400 | } | |
401 | ||
402 | } // namespace 'boost' | |
403 | </pre> | |
404 | <hr><table class="docutils field-list" frame="void" rules="none"> | |
405 | <col class="field-name" /> | |
406 | <col class="field-body" /> | |
407 | <tbody valign="top"> | |
408 | <tr class="field"><th class="field-name">Copyright:</th><td class="field-body">Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see <a class="reference" href="http://www.boost.org/LICENSE_1_0.txt">LICENSE_1_0.txt</a>).</td> | |
409 | </tr> | |
410 | </tbody> | |
411 | </table> | |
412 | </div> | |
413 | </body> | |
414 | </html> |