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   <h1>Improved Function Object Adapters</h1>

   <p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
   provides enhancements to the function object adapters specified in the C++
   Standard Library (sections 20.3.5, through to 20.3.8). The enhancements are
   principally possible due to two changes:</p>

   <ol>
     <li>We use the Boost <tt><a href=
     "../utility/call_traits.htm">call_traits</a></tt> templates to avoid the
     problem of <a href="binders.html#refref">references to references</a>,
     and to improve the efficiency of <a href="mem_fun.html#args">parameter
     passing</a>.</li>

     <li>We use two <a href="function_traits.html">function object traits</a>
     class templates to avoid the need for <tt><a href=
     "ptr_fun.html">ptr_fun</a></tt> with the adapters in this library.</li>
   </ol>

   <h3>Contents</h3>

   <p>The header contains the following function and class templates:</p>

   <table border="1" cellpadding="5" summary="">
     <tr>
       <th align="left"><a href="function_traits.html">Function object
       traits</a></th>

       <td valign="top"><tt>unary_traits<br>
       binary_traits</tt></td>

       <td valign="top">Used to determine the types of function objects' and
       functions' arguments. Eliminate the necessity for
       <tt>ptr_fun</tt>.</td>
     </tr>

     <tr>
       <th align="left"><a href="negators.html">Negators</a></th>

       <td valign="top"><tt>unary_negate<br>
       binary_negate<br>
       not1<br>
       not2</tt></td>

       <td valign="top">Based on section 20.3.5 of the standard.</td>
     </tr>

     <tr>
       <th align="left"><a href="binders.html">Binders</a></th>

       <td valign="top"><tt>binder1st<br>
       binder2nd<br>
       bind1st<br>
       bind2nd</tt></td>

       <td valign="top">Based on section 20.3.6 of the standard.</td>
     </tr>

     <tr>
       <th align="left"><a href="ptr_fun.html">Adapters for pointers to
       functions</a></th>

       <td valign="top"><tt>pointer_to_unary_function<br>
       pointer_to_binary_function<br>
       ptr_fun</tt></td>

       <td valign="top">Based on section 20.3.7 of the standard. Not required
       for use with this library since the binders and negators can adapt
       functions, but may be needed with third party adapters.</td>
     </tr>

     <tr>
       <th align="left"><a href="mem_fun.html">Adapters for pointers to member
       functions</a></th>

       <td valign="top"><tt>mem_fun_t<br>
       mem_fun1_t<br>
       const_mem_fun_t<br>
       const_mem_fun1_t<br>
       mem_fun_ref_t<br>
       mem_fun1_ref_t<br>
       const_mem_fun_ref_t<br>
       const_mem_fun1_ref_t<br>
       mem_fun<br>
       mem_fun_ref</tt></td>

       <td valign="top">Based on section 20.3.8 of the standard.</td>
     </tr>
   </table>

   <h3>Usage</h3>

   <p>Using these adapters should be pretty much the same as using the
   standard function object adapters; the only differences are that you need
   to write <tt>boost::</tt> instead of <tt>std::</tt>, and that you will get
   fewer headaches.</p>

   <p>For example, suppose you had a <tt>Person</tt> class that contained a
   <tt>set_name</tt> function:</p>

   <blockquote>
     <pre>
 class Person
 {
   public:
     void set_name(const std::string &amp;name);
   // ...
 };
 </pre>
   </blockquote>

   <p>You could rename a bunch of people in a collection, <tt>c</tt>, by
   writing</p>

   <blockquote>
     <pre>
 std::for_each(c.begin(), c.end(),
               boost::bind2nd(boost::mem_fun_ref(&amp;Person::set_name), "Fred"));
 </pre>
   </blockquote>

   <p>If the standard adapters had been used instead then this code would
   normally fail to compile, because <tt>set_name</tt> takes a reference
   argument. Refer to the comments in the <a href="binders.html#refref">binder
   documentation</a> to explain why this is so.</p>

   <h3>Compiler Compatibility</h3>

   <p>The header and <a href="test/function_test.cpp">test program</a> have been
   compiled with the following compilers:</p>

   <table border="1" cellpadding="5" summary="">
     <tr>
       <th>Compiler</th>

       <th>Comments</th>
     </tr>

     <tr>
       <td valign="top">Borland C++Builder 4 Update 2</td>

       <td valign="top">No known issues.</td>
     </tr>

     <tr>
       <td valign="top">Borland C++ 5.5</td>

       <td valign="top">No known issues.</td>
     </tr>

     <tr>
       <td valign="top">g++ 2.95.2</td>

       <td valign="top">No known issues.</td>
     </tr>

     <tr>
       <td valign="top">Microsoft Visual C++ Service Pack 3</td>

       <td valign="top">
         Compiler lacks partial specialisation, so this library offers little
         more than is provided by the standard adapters:

         <ul>
           <li>The <tt>call_traits</tt> mechanism is unable to prevent
           references to references, and so the adapters in this library will
           be usable in fewer situations.</li>

           <li>The <tt>function_traits</tt> mechanism is unable to determine
           the argument and result types of functions, therefore
           <tt>ptr_fun</tt> continues to be required to adapt functions.</li>
         </ul>
       </td>
     </tr>
   </table>

   <h3>Future Directions</h3>

   <p>This library's primary focus is to solve the problem of references to
   references while maintaining as much compatibility as possible with the
   standard library. This allows you to use the techniques you read about in
   books and magazines with many of today's compilers.</p>

   <p>In the longer term, even better solutions are likely:</p>

   <ol>
     <li>Several Boost members are working on expression template libraries.
     These will allow a more natural syntax for combining and adapting
     functions. As this is a new technology, it may be some time before it has
     matured and is widely supported by major compilers but shows great
     promise. In the meantime, the functional.hpp library fills the gap.</li>

     <li>The Standard Committee has recognised the problem of references to
     references occurring during template instantiation and has moved to fix
     the standard (see the <a href=
     "http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
     standard core language active issues list</a>).</li>
   </ol>

   <h3>Author</h3>

   <p><a href="http://www.boost.org/people/mark_rodgers.htm">Mark Rodgers</a></p>

   <h3>Acknowledgements</h3>

   <p>Thanks to <a href="http://www.boost.org/people/john_maddock.htm">John Maddock</a> for
   suggesting the mechanism that allowed the function objects traits to work
   correctly. <a href="http://www.boost.org/people/jens_maurer.htm">Jens Maurer</a> provided
   invaluable feedback during the <a href=
   "http://www.boost.org/more/formal_review_process.htm">formal review process</a>.</p>
   <hr>

   <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
   "../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional"
   height="31" width="88"></a></p>

   <p>Revised
   <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->02
   December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38510" --></p>

   <p><i>Copyright &copy; 2000 Cadenza New Zealand Ltd.</i></p>

   <p><i>Distributed under the Boost Software License, Version 1.0. (See
   accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
   copy at <a href=
   "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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	<title>Boost Function Object Adapter Library</title>
	</head>

	<body bgcolor="#FFFFFF" text="#000000">
	<table border="1" bgcolor="#007F7F" cellpadding="2" summary="">
	<tr>
	<td bgcolor="#FFFFFF"><img src="../../boost.png" alt=
	"boost.png (6897 bytes)" width="277" height="86"></td>

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	<td><a href="../../more/index.htm"><font face="Arial" color=
	"#FFFFFF"><big>More</big></font></a></td>
	</tr>
	</table>

	<h1>Improved Function Object Adapters</h1>

	<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
	provides enhancements to the function object adapters specified in the C++
	Standard Library (sections 20.3.5, through to 20.3.8). The enhancements are
	principally possible due to two changes:</p>

	<ol>
	<li>We use the Boost <tt><a href=
	"../utility/call_traits.htm">call_traits</a></tt> templates to avoid the
	problem of <a href="binders.html#refref">references to references</a>,
	and to improve the efficiency of <a href="mem_fun.html#args">parameter
	passing</a>.</li>

	<li>We use two <a href="function_traits.html">function object traits</a>
	class templates to avoid the need for <tt><a href=
	"ptr_fun.html">ptr_fun</a></tt> with the adapters in this library.</li>
	</ol>

	<h3>Contents</h3>

	<p>The header contains the following function and class templates:</p>

	<table border="1" cellpadding="5" summary="">
	<tr>
	<th align="left"><a href="function_traits.html">Function object
	traits</a></th>

	<td valign="top"><tt>unary_traits<br>
	binary_traits</tt></td>

	<td valign="top">Used to determine the types of function objects' and
	functions' arguments. Eliminate the necessity for
	<tt>ptr_fun</tt>.</td>
	</tr>

	<tr>
	<th align="left"><a href="negators.html">Negators</a></th>

	<td valign="top"><tt>unary_negate<br>
	binary_negate<br>
	not1<br>
	not2</tt></td>

	<td valign="top">Based on section 20.3.5 of the standard.</td>
	</tr>

	<tr>
	<th align="left"><a href="binders.html">Binders</a></th>

	<td valign="top"><tt>binder1st<br>
	binder2nd<br>
	bind1st<br>
	bind2nd</tt></td>

	<td valign="top">Based on section 20.3.6 of the standard.</td>
	</tr>

	<tr>
	<th align="left"><a href="ptr_fun.html">Adapters for pointers to
	functions</a></th>

	<td valign="top"><tt>pointer_to_unary_function<br>
	pointer_to_binary_function<br>
	ptr_fun</tt></td>

	<td valign="top">Based on section 20.3.7 of the standard. Not required
	for use with this library since the binders and negators can adapt
	functions, but may be needed with third party adapters.</td>
	</tr>

	<tr>
	<th align="left"><a href="mem_fun.html">Adapters for pointers to member
	functions</a></th>

	<td valign="top"><tt>mem_fun_t<br>
	mem_fun1_t<br>
	const_mem_fun_t<br>
	const_mem_fun1_t<br>
	mem_fun_ref_t<br>
	mem_fun1_ref_t<br>
	const_mem_fun_ref_t<br>
	const_mem_fun1_ref_t<br>
	mem_fun<br>
	mem_fun_ref</tt></td>

	<td valign="top">Based on section 20.3.8 of the standard.</td>
	</tr>
	</table>

	<h3>Usage</h3>

	<p>Using these adapters should be pretty much the same as using the
	standard function object adapters; the only differences are that you need
	to write <tt>boost::</tt> instead of <tt>std::</tt>, and that you will get
	fewer headaches.</p>

	<p>For example, suppose you had a <tt>Person</tt> class that contained a
	<tt>set_name</tt> function:</p>

	<blockquote>
	<pre>
	class Person
	{
	public:
	void set_name(const std::string &name);
	// ...
	};
	</pre>
	</blockquote>

	<p>You could rename a bunch of people in a collection, <tt>c</tt>, by
	writing</p>

	<blockquote>
	<pre>
	std::for_each(c.begin(), c.end(),
	boost::bind2nd(boost::mem_fun_ref(&Person::set_name), "Fred"));
	</pre>
	</blockquote>

	<p>If the standard adapters had been used instead then this code would
	normally fail to compile, because <tt>set_name</tt> takes a reference
	argument. Refer to the comments in the <a href="binders.html#refref">binder
	documentation</a> to explain why this is so.</p>

	<h3>Compiler Compatibility</h3>

	<p>The header and <a href="test/function_test.cpp">test program</a> have been
	compiled with the following compilers:</p>

	<table border="1" cellpadding="5" summary="">
	<tr>
	<th>Compiler</th>

	<th>Comments</th>
	</tr>

	<tr>
	<td valign="top">Borland C++Builder 4 Update 2</td>

	<td valign="top">No known issues.</td>
	</tr>

	<tr>
	<td valign="top">Borland C++ 5.5</td>

	<td valign="top">No known issues.</td>
	</tr>

	<tr>
	<td valign="top">g++ 2.95.2</td>

	<td valign="top">No known issues.</td>
	</tr>

	<tr>
	<td valign="top">Microsoft Visual C++ Service Pack 3</td>

	<td valign="top">
	Compiler lacks partial specialisation, so this library offers little
	more than is provided by the standard adapters:

	<ul>
	<li>The <tt>call_traits</tt> mechanism is unable to prevent
	references to references, and so the adapters in this library will
	be usable in fewer situations.</li>

	<li>The <tt>function_traits</tt> mechanism is unable to determine
	the argument and result types of functions, therefore
	<tt>ptr_fun</tt> continues to be required to adapt functions.</li>
	</ul>
	</td>
	</tr>
	</table>

	<h3>Future Directions</h3>

	<p>This library's primary focus is to solve the problem of references to
	references while maintaining as much compatibility as possible with the
	standard library. This allows you to use the techniques you read about in
	books and magazines with many of today's compilers.</p>

	<p>In the longer term, even better solutions are likely:</p>

	<ol>
	<li>Several Boost members are working on expression template libraries.
	These will allow a more natural syntax for combining and adapting
	functions. As this is a new technology, it may be some time before it has
	matured and is widely supported by major compilers but shows great
	promise. In the meantime, the functional.hpp library fills the gap.</li>

	<li>The Standard Committee has recognised the problem of references to
	references occurring during template instantiation and has moved to fix
	the standard (see the <a href=
	"http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
	standard core language active issues list</a>).</li>
	</ol>

	<h3>Author</h3>

	<p><a href="http://www.boost.org/people/mark_rodgers.htm">Mark Rodgers</a></p>

	<h3>Acknowledgements</h3>

	<p>Thanks to <a href="http://www.boost.org/people/john_maddock.htm">John Maddock</a> for
	suggesting the mechanism that allowed the function objects traits to work
	correctly. <a href="http://www.boost.org/people/jens_maurer.htm">Jens Maurer</a> provided
	invaluable feedback during the <a href=
	"http://www.boost.org/more/formal_review_process.htm">formal review process</a>.</p>
	<hr>

	<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
	"../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional"
	height="31" width="88"></a></p>

	<p>Revised
	<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->02
	December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38510" --></p>

	<p><i>Copyright © 2000 Cadenza New Zealand Ltd.</i></p>

	<p><i>Distributed under the Boost Software License, Version 1.0. (See
	accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
	copy at <a href=
	"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
	</body>
	</html>