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1 | ++++++++++++++++++++++++++++++++++ |
2 | |Boost| Pointer Container Library | |
3 | ++++++++++++++++++++++++++++++++++ | |
4 | ||
5 | .. |Boost| image:: boost.png | |
6 | ||
7 | Indirected functions | |
8 | -------------------- | |
9 | ||
10 | It is quite common that we have two pointers and what to compare the | |
11 | pointed to objects. Also, we have usually already defined how | |
12 | to compare the objects. So to avoid some tedious boiler-plate code | |
13 | this library defines predicates that apply an indirection before comparing. | |
14 | ||
15 | When the container uses ``void*`` internally, we can use the | |
16 | class ``void_ptr_indirect_fun``; otherwise we use the class | |
17 | ``indirect_fun``. | |
18 | ||
19 | **Example:** :: | |
20 | ||
21 | std::string* bar = new std::string("bar"); | |
22 | std::string* foo = new std::string("foo"); | |
23 | BOOST_ASSERT( indirect_fun< std::less<std::string> >()( bar, foo ) == true ); | |
24 | BOOST_ASSERT( make_indirect_fun( std::less<std::string>() )( foo, bar ) == false ); | |
25 | ||
26 | void* vptr1 = ptr1; | |
27 | void* vptr2 = ptr2; | |
28 | void_ptr_indirect_fun< std::less<std::string>, std::string> cast_fun; | |
29 | BOOST_CHECK( cast_fun( vptr1, vptr2 ) == true ); | |
30 | ||
31 | **See also:** | |
32 | ||
33 | - `result_of <http://www.boost.org/libs/utility/utility.htm#result_of>`_ | |
34 | - `pointee <http://www.boost.org/libs/iterator/doc/pointee.html>`_ | |
35 | - `ptr_set <ptr_set.html>`_ | |
36 | - `ptr_multiset <ptr_multiset.html>`_ | |
37 | ||
38 | **Navigate** | |
39 | ||
40 | - `home <ptr_container.html>`_ | |
41 | - `reference <reference.html>`_ | |
42 | ||
43 | **Remarks:** | |
44 | ||
45 | The class ``indirect_fun`` will work with smart pointers such as `boost::shared_ptr<T> <http://www.boost.org/libs/smart_ptr/shared_ptr.htm>`_ | |
46 | because of the type traits ``pointee<T>::type`` from the header ``<boost/pointee.hpp>``. | |
47 | ||
48 | **Synopsis:** | |
49 | ||
50 | Since the definition of the predicates is somewhat trivial, only the | |
51 | first operation is expanded inline. | |
52 | ||
53 | :: | |
54 | ||
55 | namespace boost | |
56 | { | |
57 | ||
58 | template< class Fun > | |
59 | struct indirect_fun | |
60 | { | |
61 | indirect_fun() : fun(Fun()) | |
62 | { } | |
63 | ||
64 | indirect_fun( Fun f ) : fun(f) | |
65 | { } | |
66 | ||
67 | template< class T > | |
68 | typename result_of< Fun( typename pointee<T>::type ) >::type | |
69 | operator()( const T& r ) const | |
70 | { | |
71 | return fun( *r ); | |
72 | } | |
73 | ||
74 | template< class T, class U > | |
75 | typename result_of< Fun( typename pointee<T>::type, | |
76 | typename pointee<U>::type ) >::type | |
77 | operator()( const T& r, const U& r2 ) const | |
78 | { | |
79 | return fun( *r, *r2 ); | |
80 | } | |
81 | ||
82 | private: | |
83 | Fun fun; | |
84 | }; | |
85 | ||
86 | template< class Fun > | |
87 | inline indirect_fun<Fun> make_indirect_fun( Fun f ) | |
88 | { | |
89 | return indirect_fun<Fun>( f ); | |
90 | } | |
91 | ||
92 | ||
93 | ||
94 | template< class Fun, class Arg1, class Arg2 = Arg1 > | |
95 | struct void_ptr_indirect_fun | |
96 | { | |
97 | void_ptr_indirect_fun() : fun(Fun()) | |
98 | { } | |
99 | ||
100 | void_ptr_indirect_fun( Fun f ) : fun(f) | |
101 | { } | |
102 | ||
103 | typename result_of< Fun( Arg1 ) >::type | |
104 | operator()( const void* r ) const | |
105 | { | |
106 | return fun( * static_cast<const Arg1*>( r ) ); | |
107 | } | |
108 | ||
109 | typename result_of< Fun( Arg1, Arg2 ) >::type | |
110 | operator()( const void* l, const void* r ) const | |
111 | { | |
112 | return fun( * static_cast<const Arg1*>( l ), * static_cast<const Arg2*>( r ) ); | |
113 | } | |
114 | ||
115 | private: | |
116 | Fun fun; | |
117 | }; | |
118 | ||
119 | template< class Fun, class Arg > | |
120 | inline void_ptr_indirect_fun<Fun,Arg> | |
121 | make_void_ptr_indirect_fun( Fun f ) | |
122 | { | |
123 | return void_ptr_indirect_fun<Fun,Arg>( f ); | |
124 | } | |
125 | ||
126 | } // namespace 'boost' | |
127 | ||
128 | .. raw:: html | |
129 | ||
130 | <hr> | |
131 | ||
132 | :Copyright: Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see LICENSE_1_0.txt__). | |
133 | ||
134 | __ http://www.boost.org/LICENSE_1_0.txt | |
135 | ||
136 |