1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2 3<html> 4<head> 5 <meta http-equiv="Content-Language" content="en-us"> 6 <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> 7 <meta name="GENERATOR" content="Microsoft FrontPage 6.0"> 8 <meta name="ProgId" content="FrontPage.Editor.Document"> 9 10 <title>Boost Function Object Adapter Library</title> 11</head> 12 13<body bgcolor="#FFFFFF" text="#000000"> 14 <table border="1" bgcolor="#007F7F" cellpadding="2" summary=""> 15 <tr> 16 <td bgcolor="#FFFFFF"><img src="../../boost.png" alt= 17 "boost.png (6897 bytes)" width="277" height="86"></td> 18 19 <td><a href="../../index.htm"><font face="Arial" color= 20 "#FFFFFF"><big>Home</big></font></a></td> 21 22 <td><a href="../libraries.htm"><font face="Arial" color= 23 "#FFFFFF"><big>Libraries</big></font></a></td> 24 25 <td><a href="http://www.boost.org/people/people.htm"><font face="Arial" color= 26 "#FFFFFF"><big>People</big></font></a></td> 27 28 <td><a href="http://www.boost.org/more/faq.htm"><font face="Arial" color= 29 "#FFFFFF"><big>FAQ</big></font></a></td> 30 31 <td><a href="../../more/index.htm"><font face="Arial" color= 32 "#FFFFFF"><big>More</big></font></a></td> 33 </tr> 34 </table> 35 36 <h1>Improved Function Object Adapters</h1> 37 38 <p>The header <a href="../../boost/functional.hpp">functional.hpp</a> 39 provides enhancements to the function object adapters specified in the C++ 40 Standard Library (sections 20.3.5, through to 20.3.8). The enhancements are 41 principally possible due to two changes:</p> 42 43 <ol> 44 <li>We use the Boost <tt><a href= 45 "../utility/call_traits.htm">call_traits</a></tt> templates to avoid the 46 problem of <a href="binders.html#refref">references to references</a>, 47 and to improve the efficiency of <a href="mem_fun.html#args">parameter 48 passing</a>.</li> 49 50 <li>We use two <a href="function_traits.html">function object traits</a> 51 class templates to avoid the need for <tt><a href= 52 "ptr_fun.html">ptr_fun</a></tt> with the adapters in this library.</li> 53 </ol> 54 55 <h3>Contents</h3> 56 57 <p>The header contains the following function and class templates:</p> 58 59 <table border="1" cellpadding="5" summary=""> 60 <tr> 61 <th align="left"><a href="function_traits.html">Function object 62 traits</a></th> 63 64 <td valign="top"><tt>unary_traits<br> 65 binary_traits</tt></td> 66 67 <td valign="top">Used to determine the types of function objects' and 68 functions' arguments. Eliminate the necessity for 69 <tt>ptr_fun</tt>.</td> 70 </tr> 71 72 <tr> 73 <th align="left"><a href="negators.html">Negators</a></th> 74 75 <td valign="top"><tt>unary_negate<br> 76 binary_negate<br> 77 not1<br> 78 not2</tt></td> 79 80 <td valign="top">Based on section 20.3.5 of the standard.</td> 81 </tr> 82 83 <tr> 84 <th align="left"><a href="binders.html">Binders</a></th> 85 86 <td valign="top"><tt>binder1st<br> 87 binder2nd<br> 88 bind1st<br> 89 bind2nd</tt></td> 90 91 <td valign="top">Based on section 20.3.6 of the standard.</td> 92 </tr> 93 94 <tr> 95 <th align="left"><a href="ptr_fun.html">Adapters for pointers to 96 functions</a></th> 97 98 <td valign="top"><tt>pointer_to_unary_function<br> 99 pointer_to_binary_function<br> 100 ptr_fun</tt></td> 101 102 <td valign="top">Based on section 20.3.7 of the standard. Not required 103 for use with this library since the binders and negators can adapt 104 functions, but may be needed with third party adapters.</td> 105 </tr> 106 107 <tr> 108 <th align="left"><a href="mem_fun.html">Adapters for pointers to member 109 functions</a></th> 110 111 <td valign="top"><tt>mem_fun_t<br> 112 mem_fun1_t<br> 113 const_mem_fun_t<br> 114 const_mem_fun1_t<br> 115 mem_fun_ref_t<br> 116 mem_fun1_ref_t<br> 117 const_mem_fun_ref_t<br> 118 const_mem_fun1_ref_t<br> 119 mem_fun<br> 120 mem_fun_ref</tt></td> 121 122 <td valign="top">Based on section 20.3.8 of the standard.</td> 123 </tr> 124 </table> 125 126 <h3>Usage</h3> 127 128 <p>Using these adapters should be pretty much the same as using the 129 standard function object adapters; the only differences are that you need 130 to write <tt>boost::</tt> instead of <tt>std::</tt>, and that you will get 131 fewer headaches.</p> 132 133 <p>For example, suppose you had a <tt>Person</tt> class that contained a 134 <tt>set_name</tt> function:</p> 135 136 <blockquote> 137 <pre> 138class Person 139{ 140 public: 141 void set_name(const std::string &name); 142 // ... 143}; 144</pre> 145 </blockquote> 146 147 <p>You could rename a bunch of people in a collection, <tt>c</tt>, by 148 writing</p> 149 150 <blockquote> 151 <pre> 152std::for_each(c.begin(), c.end(), 153 boost::bind2nd(boost::mem_fun_ref(&Person::set_name), "Fred")); 154</pre> 155 </blockquote> 156 157 <p>If the standard adapters had been used instead then this code would 158 normally fail to compile, because <tt>set_name</tt> takes a reference 159 argument. Refer to the comments in the <a href="binders.html#refref">binder 160 documentation</a> to explain why this is so.</p> 161 162 <h3>Compiler Compatibility</h3> 163 164 <p>The header and <a href="test/function_test.cpp">test program</a> have been 165 compiled with the following compilers:</p> 166 167 <table border="1" cellpadding="5" summary=""> 168 <tr> 169 <th>Compiler</th> 170 171 <th>Comments</th> 172 </tr> 173 174 <tr> 175 <td valign="top">Borland C++Builder 4 Update 2</td> 176 177 <td valign="top">No known issues.</td> 178 </tr> 179 180 <tr> 181 <td valign="top">Borland C++ 5.5</td> 182 183 <td valign="top">No known issues.</td> 184 </tr> 185 186 <tr> 187 <td valign="top">g++ 2.95.2</td> 188 189 <td valign="top">No known issues.</td> 190 </tr> 191 192 <tr> 193 <td valign="top">Microsoft Visual C++ Service Pack 3</td> 194 195 <td valign="top"> 196 Compiler lacks partial specialisation, so this library offers little 197 more than is provided by the standard adapters: 198 199 <ul> 200 <li>The <tt>call_traits</tt> mechanism is unable to prevent 201 references to references, and so the adapters in this library will 202 be usable in fewer situations.</li> 203 204 <li>The <tt>function_traits</tt> mechanism is unable to determine 205 the argument and result types of functions, therefore 206 <tt>ptr_fun</tt> continues to be required to adapt functions.</li> 207 </ul> 208 </td> 209 </tr> 210 </table> 211 212 <h3>Future Directions</h3> 213 214 <p>This library's primary focus is to solve the problem of references to 215 references while maintaining as much compatibility as possible with the 216 standard library. This allows you to use the techniques you read about in 217 books and magazines with many of today's compilers.</p> 218 219 <p>In the longer term, even better solutions are likely:</p> 220 221 <ol> 222 <li>Several Boost members are working on expression template libraries. 223 These will allow a more natural syntax for combining and adapting 224 functions. As this is a new technology, it may be some time before it has 225 matured and is widely supported by major compilers but shows great 226 promise. In the meantime, the functional.hpp library fills the gap.</li> 227 228 <li>The Standard Committee has recognised the problem of references to 229 references occurring during template instantiation and has moved to fix 230 the standard (see the <a href= 231 "http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#106">C++ 232 standard core language active issues list</a>).</li> 233 </ol> 234 235 <h3>Author</h3> 236 237 <p><a href="http://www.boost.org/people/mark_rodgers.htm">Mark Rodgers</a></p> 238 239 <h3>Acknowledgements</h3> 240 241 <p>Thanks to <a href="http://www.boost.org/people/john_maddock.htm">John Maddock</a> for 242 suggesting the mechanism that allowed the function objects traits to work 243 correctly. <a href="http://www.boost.org/people/jens_maurer.htm">Jens Maurer</a> provided 244 invaluable feedback during the <a href= 245 "http://www.boost.org/more/formal_review_process.htm">formal review process</a>.</p> 246 <hr> 247 248 <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src= 249 "../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional" 250 height="31" width="88"></a></p> 251 252 <p>Revised 253 <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->02 254 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38510" --></p> 255 256 <p><i>Copyright © 2000 Cadenza New Zealand Ltd.</i></p> 257 258 <p><i>Distributed under the Boost Software License, Version 1.0. (See 259 accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or 260 copy at <a href= 261 "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p> 262</body> 263</html> 264
