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 287 </style>
 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(&quot;bar&quot;);
 303 std::string* foo = new std::string(&quot;foo&quot;);
 304 BOOST_ASSERT( indirect_fun&lt; std::less&lt;std::string&gt; &gt;()( bar, foo ) == true );
 305 BOOST_ASSERT( make_indirect_fun( std::less&lt;std::string&gt;() )( foo, bar ) == false );
 306
 307 void*       vptr1  = ptr1;
 308 void*       vptr2  = ptr2;
 309 void_ptr_indirect_fun&lt; std::less&lt;std::string&gt;, std::string&gt; 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&lt;T&gt;</a>
 326 because of the type traits <tt class="docutils literal"><span class="pre">pointee&lt;T&gt;::type</span></tt> from the header <tt class="docutils literal"><span class="pre">&lt;boost/pointee.hpp&gt;</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&lt; class Fun &gt;
 335     struct indirect_fun
 336     {
 337         indirect_fun() : fun(Fun())
 338         { }
 339
 340         indirect_fun( Fun f ) : fun(f)
 341         { }
 342
 343         template&lt; class T &gt;
 344         typename result_of&lt; Fun( typename pointee&lt;T&gt;::type ) &gt;::type
 345         operator()( const T&amp; r ) const
 346         {
 347             return fun( *r );
 348         }
 349
 350         template&lt; class T, class U &gt;
 351         typename result_of&lt; Fun( typename pointee&lt;T&gt;::type,
 352                                  typename pointee&lt;U&gt;::type ) &gt;::type
 353         operator()( const T&amp; r, const U&amp; r2 ) const
 354         {
 355             return fun( *r, *r2 );
 356         }
 357
 358     private:
 359         Fun fun;
 360     };
 361
 362     template&lt; class Fun &gt;
 363     inline indirect_fun&lt;Fun&gt; make_indirect_fun( Fun f )
 364     {
 365         return indirect_fun&lt;Fun&gt;( f );
 366     }
 367
 368
 369
 370     template&lt; class Fun, class Arg1, class Arg2 = Arg1 &gt;
 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&lt; Fun( Arg1 ) &gt;::type
 380         operator()( const void* r ) const
 381         {
 382             return fun( * static_cast&lt;const Arg1*&gt;( r ) );
 383         }
 384
 385         typename result_of&lt; Fun( Arg1, Arg2 ) &gt;::type
 386         operator()( const void* l, const void* r ) const
 387         {
 388             return fun( * static_cast&lt;const Arg1*&gt;( l ), * static_cast&lt;const Arg2*&gt;( r ) );
 389         }
 390
 391     private:
 392         Fun fun;
 393     };
 394
 395     template&lt; class Fun, class Arg &gt;
 396     inline void_ptr_indirect_fun&lt;Fun,Arg&gt;
 397     make_void_ptr_indirect_fun( Fun f )
 398     {
 399         return void_ptr_indirect_fun&lt;Fun,Arg&gt;( 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>