269 lines
8.7 KiB
HTML
Executable file
269 lines
8.7 KiB
HTML
Executable file
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
|
|
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Language" content="en-us">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
|
|
<meta name="GENERATOR" content="Microsoft FrontPage 6.0">
|
|
<meta name="ProgId" content="FrontPage.Editor.Document">
|
|
|
|
<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>
|
|
|
|
<td><a href="../../index.htm"><font face="Arial" color=
|
|
"#FFFFFF"><big>Home</big></font></a></td>
|
|
|
|
<td><a href="../libraries.htm"><font face="Arial" color=
|
|
"#FFFFFF"><big>Libraries</big></font></a></td>
|
|
|
|
<td><a href="http://www.boost.org/people/people.htm"><font face="Arial" color=
|
|
"#FFFFFF"><big>People</big></font></a></td>
|
|
|
|
<td><a href="http://www.boost.org/more/faq.htm"><font face="Arial" color=
|
|
"#FFFFFF"><big>FAQ</big></font></a></td>
|
|
|
|
<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>
|
|
|
|
<tr>
|
|
<th align="left"><a href="identity.html">Identity</a></th>
|
|
<td valign="top"><tt>identity</tt></td>
|
|
<td valign="top">[func.identity] in ISO/IEC 14882:2020</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://www.open-std.org/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>
|