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| </head> |
| <body> |
| <div class="document" id="boost-pointer-container-library"> |
| <h1 class="title"><img alt="Boost" src="boost.png" /> Pointer Container Library</h1> |
| <h2 class="subtitle" id="indirected-functions">Indirected functions</h2> |
| <p>It is quite common that we have two pointers and what to compare the |
| pointed to objects. Also, we have usually already defined how |
| to compare the objects. So to avoid some tedious boiler-plate code |
| this library defines predicates that apply an indirection before comparing.</p> |
| <p>When the container uses <tt class="docutils literal"><span class="pre">void*</span></tt> internally, we can use the |
| class <tt class="docutils literal"><span class="pre">void_ptr_indirect_fun</span></tt>; otherwise we use the class |
| <tt class="docutils literal"><span class="pre">indirect_fun</span></tt>.</p> |
| <p><strong>Example:</strong></p> |
| <pre class="literal-block"> |
| std::string* bar = new std::string("bar"); |
| std::string* foo = new std::string("foo"); |
| BOOST_ASSERT( indirect_fun< std::less<std::string> >()( bar, foo ) == true ); |
| BOOST_ASSERT( make_indirect_fun( std::less<std::string>() )( foo, bar ) == false ); |
| |
| void* vptr1 = ptr1; |
| void* vptr2 = ptr2; |
| void_ptr_indirect_fun< std::less<std::string>, std::string> cast_fun; |
| BOOST_CHECK( cast_fun( vptr1, vptr2 ) == true ); |
| </pre> |
| <p><strong>See also:</strong></p> |
| <ul class="simple"> |
| <li><a class="reference" href="http://www.boost.org/libs/utility/utility.htm#result_of">result_of</a></li> |
| <li><a class="reference" href="http://www.boost.org/libs/iterator/doc/pointee.html">pointee</a></li> |
| <li><a class="reference" href="ptr_set.html">ptr_set</a></li> |
| <li><a class="reference" href="ptr_multiset.html">ptr_multiset</a></li> |
| </ul> |
| <p><strong>Navigate</strong></p> |
| <ul class="simple"> |
| <li><a class="reference" href="ptr_container.html">home</a></li> |
| <li><a class="reference" href="reference.html">reference</a></li> |
| </ul> |
| <p><strong>Remarks:</strong></p> |
| <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> |
| 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> |
| <p><strong>Synopsis:</strong></p> |
| <p>Since the definition of the predicates is somewhat trivial, only the |
| first operation is expanded inline.</p> |
| <pre class="literal-block"> |
| namespace boost |
| { |
| |
| template< class Fun > |
| struct indirect_fun |
| { |
| indirect_fun() : fun(Fun()) |
| { } |
| |
| indirect_fun( Fun f ) : fun(f) |
| { } |
| |
| template< class T > |
| typename result_of< Fun( typename pointee<T>::type ) >::type |
| operator()( const T& r ) const |
| { |
| return fun( *r ); |
| } |
| |
| template< class T, class U > |
| typename result_of< Fun( typename pointee<T>::type, |
| typename pointee<U>::type ) >::type |
| operator()( const T& r, const U& r2 ) const |
| { |
| return fun( *r, *r2 ); |
| } |
| |
| private: |
| Fun fun; |
| }; |
| |
| template< class Fun > |
| inline indirect_fun<Fun> make_indirect_fun( Fun f ) |
| { |
| return indirect_fun<Fun>( f ); |
| } |
| |
| |
| |
| template< class Fun, class Arg1, class Arg2 = Arg1 > |
| struct void_ptr_indirect_fun |
| { |
| void_ptr_indirect_fun() : fun(Fun()) |
| { } |
| |
| void_ptr_indirect_fun( Fun f ) : fun(f) |
| { } |
| |
| typename result_of< Fun( Arg1 ) >::type |
| operator()( const void* r ) const |
| { |
| return fun( * static_cast<const Arg1*>( r ) ); |
| } |
| |
| typename result_of< Fun( Arg1, Arg2 ) >::type |
| operator()( const void* l, const void* r ) const |
| { |
| return fun( * static_cast<const Arg1*>( l ), * static_cast<const Arg2*>( r ) ); |
| } |
| |
| private: |
| Fun fun; |
| }; |
| |
| template< class Fun, class Arg > |
| inline void_ptr_indirect_fun<Fun,Arg> |
| make_void_ptr_indirect_fun( Fun f ) |
| { |
| return void_ptr_indirect_fun<Fun,Arg>( f ); |
| } |
| |
| } // namespace 'boost' |
| </pre> |
| <hr><table class="docutils field-list" frame="void" rules="none"> |
| <col class="field-name" /> |
| <col class="field-body" /> |
| <tbody valign="top"> |
| <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> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </body> |
| </html> |
