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| 10 | <title>Boost Function Object Adapter Library</title> |
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| 12 | |
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| 13 | <body bgcolor="#FFFFFF" text="#000000"> |
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| 14 | <table border="1" bgcolor="#007F7F" cellpadding="2" summary=""> |
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| 15 | <tr> |
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| 16 | <td bgcolor="#FFFFFF"><img src="../../boost.png" alt= |
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| 18 | |
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| 19 | <td><a href="../../index.htm"><font face="Arial" color= |
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| 20 | "#FFFFFF"><big>Home</big></font></a></td> |
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| 21 | |
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| 22 | <td><a href="../libraries.htm"><font face="Arial" color= |
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| 23 | "#FFFFFF"><big>Libraries</big></font></a></td> |
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| 24 | |
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| 25 | <td><a href="../../people/people.htm"><font face="Arial" color= |
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| 26 | "#FFFFFF"><big>People</big></font></a></td> |
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| 27 | |
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| 28 | <td><a href="../../more/faq.htm"><font face="Arial" color= |
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| 29 | "#FFFFFF"><big>FAQ</big></font></a></td> |
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| 30 | |
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| 31 | <td><a href="../../more/index.htm"><font face="Arial" color= |
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| 32 | "#FFFFFF"><big>More</big></font></a></td> |
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| 33 | </tr> |
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| 34 | </table> |
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| 35 | |
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| 36 | <h1>Improved Function Object Adapters</h1> |
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| 37 | |
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| 38 | <p>The header <a href="../../boost/functional.hpp">functional.hpp</a> |
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| 39 | provides enhancements to the function object adapters specified in the C++ |
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| 40 | Standard Library (sections 20.3.5, through to 20.3.8). The enhancements are |
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| 41 | principally possible due to two changes:</p> |
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| 42 | |
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| 43 | <ol> |
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| 44 | <li>We use the Boost <tt><a href= |
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| 45 | "../utility/call_traits.htm">call_traits</a></tt> templates to avoid the |
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| 46 | problem of <a href="binders.html#refref">references to references</a>, |
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| 47 | and to improve the efficiency of <a href="mem_fun.html#args">parameter |
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| 48 | passing</a>.</li> |
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| 49 | |
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| 50 | <li>We use two <a href="function_traits.html">function object traits</a> |
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| 51 | class templates to avoid the need for <tt><a href= |
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| 52 | "ptr_fun.html">ptr_fun</a></tt> with the adapters in this library.</li> |
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| 53 | </ol> |
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| 54 | |
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| 55 | <h3>Contents</h3> |
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| 56 | |
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| 57 | <p>The header contains the following function and class templates:</p> |
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| 58 | |
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| 59 | <table border="1" cellpadding="5" summary=""> |
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| 60 | <tr> |
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| 61 | <th align="left"><a href="function_traits.html">Function object |
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| 62 | traits</a></th> |
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| 63 | |
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| 64 | <td valign="top"><tt>unary_traits<br> |
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| 65 | binary_traits</tt></td> |
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| 66 | |
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| 67 | <td valign="top">Used to determine the types of function objects' and |
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| 68 | functions' arguments. Eliminate the necessity for |
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| 69 | <tt>ptr_fun</tt>.</td> |
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| 70 | </tr> |
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| 71 | |
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| 72 | <tr> |
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| 73 | <th align="left"><a href="negators.html">Negators</a></th> |
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| 74 | |
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| 75 | <td valign="top"><tt>unary_negate<br> |
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| 76 | binary_negate<br> |
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| 77 | not1<br> |
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| 78 | not2</tt></td> |
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| 79 | |
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| 80 | <td valign="top">Based on section 20.3.5 of the standard.</td> |
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| 81 | </tr> |
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| 82 | |
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| 83 | <tr> |
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| 84 | <th align="left"><a href="binders.html">Binders</a></th> |
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| 85 | |
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| 86 | <td valign="top"><tt>binder1st<br> |
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| 87 | binder2nd<br> |
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| 88 | bind1st<br> |
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| 89 | bind2nd</tt></td> |
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| 90 | |
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| 91 | <td valign="top">Based on section 20.3.6 of the standard.</td> |
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| 92 | </tr> |
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| 93 | |
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| 94 | <tr> |
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| 95 | <th align="left"><a href="ptr_fun.html">Adapters for pointers to |
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| 96 | functions</a></th> |
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| 97 | |
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| 98 | <td valign="top"><tt>pointer_to_unary_function<br> |
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| 99 | pointer_to_binary_function<br> |
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| 100 | ptr_fun</tt></td> |
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| 101 | |
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| 102 | <td valign="top">Based on section 20.3.7 of the standard. Not required |
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| 103 | for use with this library since the binders and negators can adapt |
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| 104 | functions, but may be needed with third party adapters.</td> |
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| 105 | </tr> |
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| 106 | |
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| 107 | <tr> |
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| 108 | <th align="left"><a href="mem_fun.html">Adapters for pointers to member |
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| 109 | functions</a></th> |
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| 110 | |
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| 111 | <td valign="top"><tt>mem_fun_t<br> |
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| 112 | mem_fun1_t<br> |
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| 113 | const_mem_fun_t<br> |
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| 114 | const_mem_fun1_t<br> |
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| 115 | mem_fun_ref_t<br> |
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| 116 | mem_fun1_ref_t<br> |
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| 117 | const_mem_fun_ref_t<br> |
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| 118 | const_mem_fun1_ref_t<br> |
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| 119 | mem_fun<br> |
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| 120 | mem_fun_ref</tt></td> |
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| 121 | |
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| 122 | <td valign="top">Based on section 20.3.8 of the standard.</td> |
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| 123 | </tr> |
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| 124 | </table> |
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| 125 | |
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| 126 | <h3>Usage</h3> |
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| 127 | |
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| 128 | <p>Using these adapters should be pretty much the same as using the |
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| 129 | standard function object adapters; the only differences are that you need |
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| 130 | to write <tt>boost::</tt> instead of <tt>std::</tt>, and that you will get |
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| 131 | fewer headaches.</p> |
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| 132 | |
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| 133 | <p>For example, suppose you had a <tt>Person</tt> class that contained a |
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| 134 | <tt>set_name</tt> function:</p> |
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| 135 | |
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| 136 | <blockquote> |
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| 137 | <pre> |
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| 138 | class Person |
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| 139 | { |
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| 140 | public: |
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| 141 | void set_name(const std::string &name); |
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| 142 | // ... |
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| 143 | }; |
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| 144 | </pre> |
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| 145 | </blockquote> |
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| 146 | |
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| 147 | <p>You could rename a bunch of people in a collection, <tt>c</tt>, by |
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| 148 | writing</p> |
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| 149 | |
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| 150 | <blockquote> |
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| 151 | <pre> |
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| 152 | std::for_each(c.begin(), c.end(), |
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| 153 | boost::bind2nd(boost::mem_fun_ref(&Person::set_name), "Fred")); |
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| 154 | </pre> |
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| 155 | </blockquote> |
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| 156 | |
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| 157 | <p>If the standard adapters had been used instead then this code would |
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| 158 | normally fail to compile, because <tt>set_name</tt> takes a reference |
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| 159 | argument. Refer to the comments in the <a href="binders.html#refref">binder |
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| 160 | documentation</a> to explain why this is so.</p> |
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| 161 | |
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| 162 | <h3>Compiler Compatibility</h3> |
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| 163 | |
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| 164 | <p>The header and <a href="function_test.cpp">test program</a> have been |
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| 165 | compiled with the following compilers:</p> |
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| 166 | |
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| 167 | <table border="1" cellpadding="5" summary=""> |
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| 168 | <tr> |
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| 169 | <th>Compiler</th> |
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| 170 | |
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| 171 | <th>Comments</th> |
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| 172 | </tr> |
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| 173 | |
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| 174 | <tr> |
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| 175 | <td valign="top">Borland C++Builder 4 Update 2</td> |
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| 176 | |
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| 177 | <td valign="top">No known issues.</td> |
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| 178 | </tr> |
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| 179 | |
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| 180 | <tr> |
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| 181 | <td valign="top">Borland C++ 5.5</td> |
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| 182 | |
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| 183 | <td valign="top">No known issues.</td> |
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| 184 | </tr> |
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| 185 | |
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| 186 | <tr> |
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| 187 | <td valign="top">g++ 2.95.2</td> |
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| 188 | |
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| 189 | <td valign="top">No known issues.</td> |
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| 190 | </tr> |
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| 191 | |
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| 192 | <tr> |
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| 193 | <td valign="top">Microsoft Visual C++ Service Pack 3</td> |
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| 194 | |
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| 195 | <td valign="top"> |
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| 196 | Compiler lacks partial specialisation, so this library offers little |
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| 197 | more than is provided by the standard adapters: |
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| 198 | |
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| 199 | <ul> |
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| 200 | <li>The <tt>call_traits</tt> mechanism is unable to prevent |
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| 201 | references to references, and so the adapters in this library will |
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| 202 | be usable in fewer situations.</li> |
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| 203 | |
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| 204 | <li>The <tt>function_traits</tt> mechanism is unable to determine |
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| 205 | the argument and result types of functions, therefore |
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| 206 | <tt>ptr_fun</tt> continues to be required to adapt functions.</li> |
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| 207 | </ul> |
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| 208 | </td> |
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| 209 | </tr> |
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| 210 | </table> |
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| 211 | |
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| 212 | <h3>Future Directions</h3> |
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| 213 | |
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| 214 | <p>This library's primary focus is to solve the problem of references to |
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| 215 | references while maintaining as much compatibility as possible with the |
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| 216 | standard library. This allows you to use the techniques you read about in |
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| 217 | books and magazines with many of today's compilers.</p> |
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| 218 | |
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| 219 | <p>In the longer term, even better solutions are likely:</p> |
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| 220 | |
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| 221 | <ol> |
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| 222 | <li>Several Boost members are working on expression template libraries. |
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| 223 | These will allow a more natural syntax for combining and adapting |
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| 224 | functions. As this is a new technology, it may be some time before it has |
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| 225 | matured and is widely supported by major compilers but shows great |
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| 226 | promise. In the meantime, the functional.hpp library fills the gap.</li> |
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| 227 | |
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| 228 | <li>The Standard Committee has recognised the problem of references to |
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| 229 | references occurring during template instantiation and has moved to fix |
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| 230 | the standard (see the <a href= |
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| 231 | "http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++ |
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| 232 | standard core language active issues list</a>).</li> |
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| 233 | </ol> |
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| 234 | |
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| 235 | <h3>Author</h3> |
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| 236 | |
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| 237 | <p><a href="../../people/mark_rodgers.htm">Mark Rodgers</a></p> |
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| 238 | |
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| 239 | <h3>Acknowledgements</h3> |
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| 240 | |
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| 241 | <p>Thanks to <a href="../../people/john_maddock.htm">John Maddock</a> for |
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| 242 | suggesting the mechanism that allowed the function objects traits to work |
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| 243 | correctly. <a href="../../people/jens_maurer.htm">Jens Maurer</a> provided |
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| 244 | invaluable feedback during the <a href= |
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| 245 | "../../more/formal_review_process.htm">formal review process</a>.</p> |
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| 246 | <hr> |
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| 247 | |
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| 248 | <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src= |
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| 249 | "http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional" |
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| 250 | height="31" width="88"></a></p> |
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| 251 | |
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| 252 | <p>Revised |
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| 253 | <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->02 |
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| 254 | December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38510" --></p> |
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| 255 | |
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| 256 | <p><i>Copyright © 2000 Cadenza New Zealand Ltd.</i></p> |
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| 257 | |
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| 258 | <p><i>Distributed under the Boost Software License, Version 1.0. (See |
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| 259 | accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or |
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| 260 | copy at <a href= |
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| 261 | "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p> |
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| 262 | </body> |
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| 263 | </html> |
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