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<h1>Binders</h1>
<td><a href="../libraries.htm"><font face="Arial" color=
"#FFFFFF"><big>Libraries</big></font></a></td>
<p>The header <nobr><a
href="../../boost/functional.hpp">functional.hpp</a></nobr> provides
enhanced versions of both the binder function object adapters from the
C++ Standard Library <nobr>(&sect;20.3.6):</nobr></p>
<td><a href="../../people/people.htm"><font face="Arial" color=
"#FFFFFF"><big>People</big></font></a></td>
<ul>
<li><tt>binder1st</tt></li>
<li><tt>binder2nd</tt></li>
</ul>
<td><a href="../../more/faq.htm"><font face="Arial" color=
"#FFFFFF"><big>FAQ</big></font></a></td>
<p>As well as the corresponding helper functions</p>
<td><a href="../../more/index.htm"><font face="Arial" color=
"#FFFFFF"><big>More</big></font></a></td>
</tr>
</table>
<ul>
<li><tt>bind1st</tt></li>
<li><tt>bind2nd</tt></li>
</ul>
<h1>Binders</h1>
<p>The key benefit of these adapters over those in the Standard
Library is they avoid the problem of <a href="#refref">references to
references.</a>
<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
provides enhanced versions of both the binder function object adapters from
the C++ Standard Library (&sect;20.3.6):</p>
<h3>Usage</h3>
<ul>
<li><tt>binder1st</tt></li>
<p>Usage is identical to the standard binders. For example,</p>
<li><tt>binder2nd</tt></li>
</ul>
<blockquote><pre>
<p>As well as the corresponding helper functions</p>
<ul>
<li><tt>bind1st</tt></li>
<li><tt>bind2nd</tt></li>
</ul>
<p>The key benefit of these adapters over those in the Standard Library is
they avoid the problem of <a href="#refref">references to
references.</a></p>
<h3>Usage</h3>
<p>Usage is identical to the standard binders. For example,</p>
<blockquote>
<pre>
class Foo {
public:
void bar(std::ostream &);
void bar(std::ostream &amp;);
// ...
};
// ...
std::vector&lt;Foo&gt; c;
// ...
std::for_each(c.begin(), c.end(),
boost::bind2nd(boost::mem_fun_ref(&Foo::bar), std::cout));
</pre></blockquote>
boost::bind2nd(boost::mem_fun_ref(&amp;Foo::bar), std::cout));
</pre>
</blockquote>
<h3 id="refref">References to References</h3>
<h3 id="refref">References to References</h3>
<p>Consider the usage example above</p>
<p>Consider the usage example above</p>
<blockquote><pre>
<blockquote>
<pre>
class Foo {
public:
void bar(<strong>std::ostream &</strong>);
void bar(<strong>std::ostream &amp;</strong>);
// ...
};
// ...
std::for_each(c.begin(), c.end(),
boost::bind2nd(boost::mem_fun_ref(&Foo::bar), std::cout));
</pre></blockquote>
boost::bind2nd(boost::mem_fun_ref(&amp;Foo::bar), std::cout));
</pre>
</blockquote>
<p>If this had been written using <tt><nobr>std::bind2nd</nobr></tt>
and <tt><nobr>std::mem_fun_ref</nobr></tt>, it would be unlikely to
compile.</p>
<p>If this had been written using <tt>std::bind2nd</tt> and
<tt>std::mem_fun_ref</tt>, it would be unlikely to compile.</p>
<p>The problem arises because <tt><nobr>bar</nobr></tt> takes a
reference argument. The Standard defines
<tt><nobr>std::mem_fun_ref</nobr></tt> such that it creates a function
object whose <tt><nobr>second_argument_type</nobr></tt> will be
<tt><nobr>std::ostream&</nobr></tt>.</p>
<p>The problem arises because <tt>bar</tt> takes a reference argument. The
Standard defines <tt>std::mem_fun_ref</tt> such that it creates a function
object whose <tt>second_argument_type</tt> will be
<tt>std::ostream&amp;</tt>.</p>
<p>The call to <tt><nobr>bind2nd</nobr></tt> creates a
<tt><nobr>binder2nd</nobr></tt> which the Standard defines as follows:
<p>The call to <tt>bind2nd</tt> creates a <tt>binder2nd</tt> which the
Standard defines as follows:</p>
<blockquote><pre>
<blockquote>
<pre>
template &lt;class Operation&gt;
class binder2nd
: public unary_function&lt;typename Operation::first_argument_type,
typename Operation::result_type&gt; {
...
public:
binder2nd(const Operation& x,
<strong>const typename Operation::second_argument_type& y</strong>);
binder2nd(const Operation&amp; x,
<strong>const typename Operation::second_argument_type&amp; y</strong>);
...
</pre></blockquote>
</pre>
</blockquote>
<p>Since our operation's <tt><nobr>second_argument_type</nobr></tt> is
<tt><nobr>std::ostream&</nobr></tt>, the type of <tt>y</tt> in the
constructor would be <tt><nobr>std::ostream&&</nobr></tt>. Since you
cannot have a reference to a reference, at this point we should get a
compilation error because references to references are illegal in C++
(but see <a
href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">
C++ Standard core language active issues list</a>).</p>
<p>Since our operation's <tt>second_argument_type</tt> is
<tt>std::ostream&amp;</tt>, the type of <tt>y</tt> in the constructor would
be <tt>std::ostream&amp;&amp;</tt>. Since you cannot have a reference to a
reference, at this point we should get a compilation error because
references to references are illegal in C++ (but see <a href=
"http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
Standard core language active issues list</a>).</p>
<p>The binders in this library avoid this problem by using the Boost
<nobr><tt><a
href="../utility/call_traits.htm">call_traits</a></tt></nobr> templates.</p>
<p>The binders in this library avoid this problem by using the Boost
<tt><a href="../utility/call_traits.htm">call_traits</a></tt>
templates.</p>
<p>Our constructor is declared
<p>Our constructor is declared</p>
<blockquote><pre>
binder2nd(const Operation& x,
<blockquote>
<pre>
binder2nd(const Operation&amp; x,
<strong>typename call_traits&lt;
typename binary_traits&lt;Operation&gt;::second_argument_type
&gt;::param_type y</strong>)
</pre></blockquote>
</pre>
</blockquote>
<p>As a result, <tt>y</tt> has a type of <tt><nobr>std::ostream&</nobr></tt>,
and our example compiles.</p>
<p>As a result, <tt>y</tt> has a type of <tt>std::ostream&amp;</tt>, and
our example compiles.</p>
<hr>
<hr>
<p>Copyright &copy; 2000 Cadenza New Zealand Ltd. Permission to copy, use, modify, sell and distribute this document is granted provided this copyright notice appears in all copies. This document is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose.</p>
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<p>Revised 28 June 2000</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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// ------------------------------------------------------------------------------
// Copyright (c) 2000 Cadenza New Zealand Ltd
// Distributed under the Boost Software License, Version 1.0. (See accompany-
// ing file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// ------------------------------------------------------------------------------
// Tests for the Boost functional.hpp header file
//
// Note that functional.hpp relies on partial specialisation to be
// effective. If your compiler lacks this feature, very few of the
// tests would compile, and so have been excluded from the test.
// ------------------------------------------------------------------------------
// Copyright (c) 2000
// Cadenza New Zealand Ltd
//
// Permission to use, copy, modify, distribute and sell this software
// and its documentation for any purpose is hereby granted without
// fee, provided that the above copyright notice appears in all copies
// and that both the copyright notice and this permission notice
// appear in supporting documentation. Cadenza New Zealand Ltd makes
// no representations about the suitability of this software for any
// purpose. It is provided "as is" without express or implied
// warranty.
// ------------------------------------------------------------------------------
// $Id$
// ------------------------------------------------------------------------------
// $Log$
// Revision 1.2.24.1 2006/12/02 14:17:26 andreas_huber69
// Merged L & C issue fixes from trunk to branch.
//
// Revision 1.3 2006/12/02 13:57:32 andreas_huber69
// Fixed license & copyright issues.
//
// From Mark Rodgers Fri Dec 1 12:59:14 2006
// X-Apparently-To: ahd6974-boostorg -at- yahoo.com via 68.142.206.160; Fri, 01 Dec 2006 12:59:41 -0800
// X-Originating-IP: [195.112.4.54]
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// Received: from penfold.cadenza.co.nz ([192.168.55.56]) by snagglepuss.cadenza.co.nz with esmtp (Exim 4.63) (envelope-from <mark.rodgers -at- cadenza.co.nz>) id J9M4Y9-0009TO-9K for ahd6974-boostorg -at- yahoo.com; Fri, 01 Dec 2006 20:58:57 +0000
// Message-ID: <457097A2.1090305@cadenza.co.nz>
// Date: Fri, 01 Dec 2006 20:59:14 +0000
// From: "Mark Rodgers" <mark.rodgers -at- cadenza.co.nz>
// User-Agent: Thunderbird 1.5.0.8 (Macintosh/20061025)
// MIME-Version: 1.0
// To: ahd6974-boostorg -at- yahoo.com [Edit - Delete]
// Subject: Re: [boost] Reminder: Need your permission to correct license & copyright issues
// References: <379990.36007.qm@web33507.mail.mud.yahoo.com>
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// Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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// Gidday Andreas
//
// Sure that's fine. I'm happy for you to do 1, 2 and 3.
//
// Regards
// Mark
//
// Andreas Huber wrote:
// > Hello Mark
// >
// > Quite a while ago it was decided that every file that goes into the
// > 1.34 release of the Boost distribution (www.boost.org) needs uniform
// > license and copyright information. For more information please see:
// >
// > <http://www.boost.org/more/license_info.html>
// >
// > You are receiving this email because several files you contributed
// > lack such information or have an old license:
// >
// > boost/functional/functional.hpp
// > boost/libs/functional/binders.html
// > boost/libs/functional/function_test.cpp
// > boost/libs/functional/function_traits.html
// > boost/libs/functional/index.html
// > boost/libs/functional/mem_fun.html
// > boost/libs/functional/negators.html
// > boost/libs/functional/ptr_fun.html
// > boost/people/mark_rodgers.htm
// >
// > I therefore kindly ask you to grant the permission to do the
// > following:
// >
// > 1. For the files above that already have a license text (all except
// > mark_rodgers.htm), replace the license text with:
// >
// > "Distributed under the Boost Software License, Version 1.0. (See
// > accompanying file LICENSE_1_0.txt or copy at
// > http://www.boost.org/LICENSE_1_0.txt)"
// >
// > 2. For the file that does not yet have a license and copyright
// > (mark_rodgers.htm) add the same license text as under 1. and add the
// > following copyright:
// >
// > "(c) Copyright Mark Rodgers 2000"
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// >
// > It would be great if you could grant me permission to do 1 & 2 and
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// > Thank you!
// >
// > Regards,
// >
// > Andreas Huber
// >
//
// Revision 1.2 2001/09/22 11:52:24 johnmaddock
// Intel C++ fixes: no void return types supported.
//

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<h1>Function Object Traits</h1>
<td><a href="../libraries.htm"><font face="Arial" color=
"#FFFFFF"><big>Libraries</big></font></a></td>
<p>The header <nobr><a
href="../../boost/functional.hpp">functional.hpp</a></nobr> provides two
traits class templates for functions and function objects:</p>
<td><a href="../../people/people.htm"><font face="Arial" color=
"#FFFFFF"><big>People</big></font></a></td>
<table border="1">
<tr>
<th>Type</th>
<th>Contents</th>
<th>Description</th>
</tr>
<tr>
<td valign="top" rowspan="4"><tt><nobr>template &lt;typename T&gt;</nobr><br><nobr>struct unary_traits<nobr></tt>
</td>
<td valign="top"><tt><nobr>function_type</nobr></tt>
</td>
<td valign="top">The type of the function or function object itself (i.e., <tt>T</tt>).
</td>
</tr>
<tr>
<td valign="top"><tt><nobr>param_type</nobr></tt>
</td>
<td valign="top">The type that should be used to pass the function or function object as a parameter.
</td>
</tr>
<tr>
<td valign="top"><tt><nobr>result_type</nobr></tt>
</td>
<td valign="top">The type returned by the function or function object.
</td>
</tr>
<tr>
<td valign="top"><tt><nobr>argument_type</nobr></tt>
</td>
<td valign="top">The type of the argument to the function or function object.
</td>
</tr>
<tr>
<td valign="top" rowspan="5"><tt><nobr>template &lt;typename T&gt;</nobr><br><nobr>struct binary_traits<nobr></tt>
</td>
<td valign="top"><tt><nobr>function_type</nobr></tt>
</td>
<td valign="top">The type of the function or function object itself (i.e., <tt>T</tt>).
</td>
</tr>
<tr>
<td valign="top"><tt><nobr>param_type</nobr></tt>
</td>
<td valign="top">The type that should be used to pass the function or function object as a parameter.
</td>
</tr>
<tr>
<td valign="top"><tt><nobr>result_type</nobr></tt>
</td>
<td valign="top">The type returned by the function or function object.
</td>
</tr>
<tr>
<td valign="top"><tt><nobr>first_argument_type</nobr></tt>
</td>
<td valign="top">The type of the first argument to the function or function object.
</td>
</tr>
<tr>
<td valign="top"><tt><nobr>second_argument_type</nobr></tt>
</td>
<td valign="top">The type of the second argument to the function or function object.
</td>
</tr>
</table>
<td><a href="../../more/faq.htm"><font face="Arial" color=
"#FFFFFF"><big>FAQ</big></font></a></td>
<h3>Usage</h3>
<td><a href="../../more/index.htm"><font face="Arial" color=
"#FFFFFF"><big>More</big></font></a></td>
</tr>
</table>
<p><tt><nobr>unary_traits</nobr></tt> should be instantiated with
either a function taking a single parameter, or an adaptable unary
function object (i.e., a class derived from
<tt><nobr>std::unary_function</nobr></tt> or one which provides the
same typedefs). (See &sect;20.3.1 in the C++ Standard.)
<h1>Function Object Traits</h1>
<p><tt><nobr>binary_traits</nobr></tt> should be instantiated with
either a function taking two parameters, or an adaptable binary
function object (i.e., a class derived from
<tt><nobr>std::binary_function</nobr></tt> or one which provides the
same typedefs). (See &sect;20.3.1 in the C++ Standard.)
<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
provides two traits class templates for functions and function objects:</p>
<p>The most common usage of these templates is in function object
adapters, thus allowing them to adapt plain functions as well as
function objects. You can do this by wherever you would normally
write, for example,
<table border="1" summary="">
<tr>
<th>Type</th>
<blockquote><pre>
<th>Contents</th>
<th>Description</th>
</tr>
<tr>
<td valign="top" rowspan="4">
<tt>template&nbsp;&lt;typename&nbsp;T&gt;<br>
struct&nbsp;unary_traits</tt></td>
<td valign="top"><tt>function_type</tt></td>
<td valign="top">The type of the function or function object itself
(i.e., <tt>T</tt>).</td>
</tr>
<tr>
<td valign="top"><tt>param_type</tt></td>
<td valign="top">The type that should be used to pass the function or
function object as a parameter.</td>
</tr>
<tr>
<td valign="top"><tt>result_type</tt></td>
<td valign="top">The type returned by the function or function
object.</td>
</tr>
<tr>
<td valign="top"><tt>argument_type</tt></td>
<td valign="top">The type of the argument to the function or function
object.</td>
</tr>
<tr>
<td valign="top" rowspan="5">
<tt>template&nbsp;&lt;typename&nbsp;T&gt;<br>
struct&nbsp;binary_traits</tt></td>
<td valign="top"><tt>function_type</tt></td>
<td valign="top">The type of the function or function object itself
(i.e., <tt>T</tt>).</td>
</tr>
<tr>
<td valign="top"><tt>param_type</tt></td>
<td valign="top">The type that should be used to pass the function or
function object as a parameter.</td>
</tr>
<tr>
<td valign="top"><tt>result_type</tt></td>
<td valign="top">The type returned by the function or function
object.</td>
</tr>
<tr>
<td valign="top"><tt>first_argument_type</tt></td>
<td valign="top">The type of the first argument to the function or
function object.</td>
</tr>
<tr>
<td valign="top"><tt>second_argument_type</tt></td>
<td valign="top">The type of the second argument to the function or
function object.</td>
</tr>
</table>
<h3>Usage</h3>
<p><tt>unary_traits</tt> should be instantiated with either a function
taking a single parameter, or an adaptable unary function object (i.e., a
class derived from <tt>std::unary_function</tt> or one which provides the
same typedefs). (See &sect;20.3.1 in the C++ Standard.)</p>
<p><tt>binary_traits</tt> should be instantiated with either a function
taking two parameters, or an adaptable binary function object (i.e., a
class derived from <tt>std::binary_function</tt> or one which provides the
same typedefs). (See &sect;20.3.1 in the C++ Standard.)</p>
<p>The most common usage of these templates is in function object adapters,
thus allowing them to adapt plain functions as well as function objects.
You can do this by wherever you would normally write, for example,</p>
<blockquote>
<pre>
typename Operation::argument_type
</pre></blockquote>
</pre>
</blockquote>
<p>simply writing
<p>simply writing</p>
<blockquote><pre>
<blockquote>
<pre>
typename boost::unary_traits&lt;Operation&gt;::argument_type
</pre></blockquote>
</pre>
</blockquote>
<p>instead.
<p>instead.</p>
<h3>Additional Types Defined</h3>
<h3>Additional Types Defined</h3>
<p>In addition to the standard result and argument typedefs, these
traits templates define two additional types.
<p>In addition to the standard result and argument typedefs, these traits
templates define two additional types.</p>
<h4><tt>function_type</tt></h4>
<h4><tt>function_type</tt></h4>
<p>This is the type of the function or function object, and can be
used in declarations such as</p>
<p>This is the type of the function or function object, and can be used in
declarations such as</p>
<blockquote><pre>
<blockquote>
<pre>
template &lt;class Predicate&gt;
class unary_negate : // ...
{
@ -139,19 +168,21 @@ class unary_negate : // ...
private:
<strong>typename unary_traits&lt;Predicate&gt;::function_type</strong> pred;
};
</pre></blockquote>
</pre>
</blockquote>
<p>If this typedef were not provided, it would not be possible to
declare <tt>pred</tt> in a way that would allow
<tt><nobr>unary_negate</nobr></tt> to be instantiated with a function
type (see the C++ Standard &sect;14.3.1 &para;3).
<p>If this typedef were not provided, it would not be possible to declare
<tt>pred</tt> in a way that would allow <tt>unary_negate</tt> to be
instantiated with a function type (see the C++ Standard &sect;14.3.1
&para;3).</p>
<h4><tt>param_type</tt></h4>
<h4><tt>param_type</tt></h4>
<p>This is a type suitable for passing the function or function object
as a parameter to another function. For example,
<p>This is a type suitable for passing the function or function object as a
parameter to another function. For example,</p>
<blockquote><pre>
<blockquote>
<pre>
template &lt;class Predicate&gt;
class unary_negate : // ...
{
@ -162,35 +193,41 @@ class unary_negate : // ...
{}
// ...
};
</pre></blockquote>
</pre>
</blockquote>
<p>Function objects are passed by reference to const; function
pointers are passed by value.</p>
<p>Function objects are passed by reference to const; function pointers are
passed by value.</p>
<h3>Limitations</h3>
<h3>Limitations</h3>
<p>This library uses these traits within all function object adapters,
theoretically rendering <tt>ptr_fun</tt> obsolete. However, third party
adapters probably won't take advantage of this mechanism, and so
<tt>ptr_fun</tt> may still be required. Accordingly, this library also
provides <a href="ptr_fun.html">improved versions of the standard function
pointer adapters</a>.</p>
<p>This library uses these traits within all function object adapters,
theoretically rendering <tt><nobr>ptr_fun</nobr></tt> obsolete.
However, third party adapters probably won't take advantage of this
mechanism, and so <tt><nobr>ptr_fun</nobr></tt> may still be required.
Accordingly, this library also provides <a
href="ptr_fun.html">improved versions of the standard function pointer
adapters</a>.</p>
<p>These traits templates will also not work with compilers that fail to
support partial specialisation of templates. With these compilers, the
traits templates can only be instantiated with adaptable function objects,
thus requiring <tt>ptr_fun</tt> to be used, even with the function object
adapters in this library.</p>
<hr>
<p>These traits templates will also not work with compilers that fail
to support partial specialisation of templates. With these compilers,
the traits templates can only be instantiated with adaptable function
objects, thus requiring <tt><nobr>ptr_fun</nobr></tt> to be used, even
with the function object adapters in this library.
<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
"http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional"
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<p>Copyright &copy; 2000 Cadenza New Zealand Ltd. Permission to copy,
use, modify, sell and distribute this document is granted provided
this copyright notice appears in all copies. This document is provided
"as is" without express or implied warranty, and with no claim as to
its suitability for any purpose.</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>Revised 28 June 2000</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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View File

@ -1,19 +1,11 @@
// ------------------------------------------------------------------------------
// Copyright (c) 2000 Cadenza New Zealand Ltd
// Distributed under the Boost Software License, Version 1.0. (See accompany-
// ing file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// ------------------------------------------------------------------------------
// Boost functional.hpp header file
// See http://www.boost.org/libs/functional for documentation.
// ------------------------------------------------------------------------------
// Copyright (c) 2000
// Cadenza New Zealand Ltd
//
// Permission to use, copy, modify, distribute and sell this software
// and its documentation for any purpose is hereby granted without
// fee, provided that the above copyright notice appears in all copies
// and that both the copyright notice and this permission notice
// appear in supporting documentation. Cadenza New Zealand Ltd makes
// no representations about the suitability of this software for any
// purpose. It is provided "as is" without express or implied
// warranty.
// ------------------------------------------------------------------------------
// $Id$
// ------------------------------------------------------------------------------

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<h1>Improved Function Object Adapters</h1>
<p>The header <nobr><a href="../../boost/functional.hpp">functional.hpp</a></nobr>
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 <nobr><tt><a href="../utility/call_traits.htm">call_traits</a></tt></nobr>
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
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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 <nobr><tt><a href="ptr_fun.html">ptr_fun</a></tt></nobr>
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">
<tr>
<th align="left"><a href="function_traits.html">Function object traits</a>
<td valign="top"><tt><nobr>unary_traits</nobr><br>
<nobr>binary_traits</nobr></tt></td>
<td valign="top">Used to determine the types of function objects' and
functions' arguments. Eliminate the necessity for <nobr><tt>ptr_fun</tt></nobr>.</td>
</tr>
<tr>
<th align="left"><a href="negators.html">Negators</a></th>
<td valign="top"><tt><nobr>unary_negate</nobr><br>
<nobr>binary_negate</nobr><br>
<nobr>not1</nobr><br>
<nobr>not2</nobr></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><nobr>binder1st</nobr><br>
<nobr>binder2nd</nobr><br>
<nobr>bind1st</nobr><br>
<nobr>bind2nd</nobr></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><nobr>pointer_to_unary_function</nobr><br>
<nobr>pointer_to_binary_function</nobr><br>
<nobr>ptr_fun</nobr></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
<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><nobr>mem_fun_t</nobr><br>
<nobr>mem_fun1_t</nobr><br>
<nobr>const_mem_fun_t</nobr><br>
<nobr>const_mem_fun1_t</nobr><br>
<nobr>mem_fun_ref_t</nobr><br>
<nobr>mem_fun1_ref_t</nobr><br>
<nobr>const_mem_fun_ref_t</nobr><br>
<nobr>const_mem_fun1_ref_t</nobr><br>
<nobr>mem_fun</nobr><br>
<nobr>mem_fun_ref</nobr></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 <nobr><tt>boost::</tt></nobr>
instead of <nobr><tt>std::</tt></nobr>, and that you will get fewer headaches.</p>
<p>For example, suppose you had a <tt>Person</tt> class that contained a <nobr><tt>set_name</tt></nobr>
function:
<blockquote>
<pre>
<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:
@ -99,86 +142,122 @@ class Person
// ...
};
</pre>
</blockquote>
<p>You could rename a bunch of people in a collection, <tt>c</tt>, by writing</p>
<blockquote>
<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), &quot;Fred&quot;));
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><nobr>set_name</nobr></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="function_test.cpp">test program</a> have been
compiled with the following compilers:</p>
<table border="1" cellpadding="5">
<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 <nobr><tt>call_traits</tt></nobr> mechanism is unable to prevent
references to references, and so the adapters in this library will be
usable in fewer situations.</li>
<li>The <nobr><tt>function_traits</tt></nobr> mechanism is unable to
determine the argument and result types of functions, therefore <nobr><tt>ptr_fun</tt></nobr>
continues to be required to adapt functions.
</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++
</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="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="../../people/mark_rodgers.htm">Mark Rodgers</a></p>
<h3>Acknowledgements</h3>
<p>Thanks to <a href="../../people/john_maddock.htm">John Maddock</a> for
suggesting the mechanism that allowed the function objects traits to work
correctly. <a href="../../people/jens_maurer.htm">Jens Maurer</a> provided
invaluable feedback during the <a href="../../more/formal_review_process.htm">formal
review process</a>.
<hr>
<p>Copyright <20> 2000 Cadenza New Zealand Ltd. Permission to copy, use, modify,
sell and distribute this document is granted provided this copyright notice
appears in all copies. This document is provided &quot;as is&quot; without
express or implied warranty, and with no claim as to its suitability for any
purpose.</p>
<p>Revised 28 June 2000</p>
</ol>
<h3>Author</h3>
<p><a href="../../people/mark_rodgers.htm">Mark Rodgers</a></p>
<h3>Acknowledgements</h3>
<p>Thanks to <a href="../../people/john_maddock.htm">John Maddock</a> for
suggesting the mechanism that allowed the function objects traits to work
correctly. <a href="../../people/jens_maurer.htm">Jens Maurer</a> provided
invaluable feedback during the <a href=
"../../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=
"http://www.w3.org/Icons/valid-html401" 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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View File

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<h1>Member Function Adapters</h1>
<td><a href="../libraries.htm"><font face="Arial" color=
"#FFFFFF"><big>Libraries</big></font></a></td>
<p>The header <nobr><a
href="../../boost/functional.hpp">functional.hpp</a></nobr> includes
improved versions of the full range of member function adapters from
the the C++ Standard Library <nobr>(&sect 20.3.8):</nobr></p>
<td><a href="../../people/people.htm"><font face="Arial" color=
"#FFFFFF"><big>People</big></font></a></td>
<ul>
<li><tt>mem_fun_t</tt></li>
<li><tt>mem_fun1_t</tt></li>
<li><tt>const_mem_fun_t</tt></li>
<li><tt>const_mem_fun1_t</tt></li>
<li><tt>mem_fun_ref_t</tt></li>
<li><tt>mem_fun1_ref_t</tt></li>
<li><tt>const_mem_fun_ref_t</tt></li>
<li><tt>const_mem_fun1_ref_t</tt></li>
</ul>
<td><a href="../../more/faq.htm"><font face="Arial" color=
"#FFFFFF"><big>FAQ</big></font></a></td>
<p>as well as the corresponding overloaded helper functions<p>
<ul>
<li><tt>mem_fun</tt></li>
<li><tt>mem_fun_ref</tt></li>
</ul>
<td><a href="../../more/index.htm"><font face="Arial" color=
"#FFFFFF"><big>More</big></font></a></td>
</tr>
</table>
<p>The following changes have been made to the adapters as specified
in the Standard:</p>
<h1>Member Function Adapters</h1>
<ul>
<li>The <tt><nobr>first_argument_type</nobr></tt> typedef has been
corrected for the <nobr><tt>const_</tt></nobr> family of member
function adapters (see <a href="#firstarg">below</a>).</li>
<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
includes improved versions of the full range of member function adapters
from the the C++ Standard Library (&sect;20.3.8):</p>
<li>The argument passed to <tt><nobr>mem_fun1_t</nobr></tt> and its
variants is passed using the
<tt><nobr>call_traits::param_type</nobr></tt> for the member
function's argument type.
</ul>
<ul>
<li><tt>mem_fun_t</tt></li>
<h3 id="firstarg">first_argument_type</h3>
<li><tt>mem_fun1_t</tt></li>
<p>The standard specifies <tt><nobr>const_mem_fun1_t</nobr></tt>, for example, like this:
<li><tt>const_mem_fun_t</tt></li>
<blockquote><pre>
<li><tt>const_mem_fun1_t</tt></li>
<li><tt>mem_fun_ref_t</tt></li>
<li><tt>mem_fun1_ref_t</tt></li>
<li><tt>const_mem_fun_ref_t</tt></li>
<li><tt>const_mem_fun1_ref_t</tt></li>
</ul>
<p>as well as the corresponding overloaded helper functions</p>
<ul>
<li><tt>mem_fun</tt></li>
<li><tt>mem_fun_ref</tt></li>
</ul>
<p>The following changes have been made to the adapters as specified in the
Standard:</p>
<ul>
<li>The <tt>first_argument_type</tt> typedef has been corrected for the
<tt>const_</tt> family of member function adapters (see <a href=
"#firstarg">below</a>).</li>
<li>The argument passed to <tt>mem_fun1_t</tt> and its variants is passed
using the <tt>call_traits::param_type</tt> for the member function's
argument type.</li>
</ul>
<h3 id="firstarg">first_argument_type</h3>
<p>The standard specifies <tt>const_mem_fun1_t</tt>, for example, like
this:</p>
<blockquote>
<pre>
template &lt;class S, class T, class A&gt; class const_mem_fun1_t
: public binary_function&lt;<strong>T*</strong>, A, S&gt; {
public:
explicit const_mem_fun1_t(S (T::*p)(A) const);
S operator()(<strong>const T*</strong> p, A x) const;
};
</pre></blockquote>
</pre>
</blockquote>
<p>Note that the first argument to
<tt><nobr>binary_function</nobr></tt> is <tt><nobr>T*</nobr></tt>
despite the fact that the first argument to <tt><nobr>operator()</nobr></tt> is
actually of type <tt><nobr><em>const</em> T*</nobr></tt>.
<p>Note that the first argument to <tt>binary_function</tt> is <tt>T*</tt>
despite the fact that the first argument to <tt>operator()</tt> is actually
of type <tt><em>const</em>&nbsp;T*</tt>.</p>
<p>Does this matter? Well, consider what happens when we write
<p>Does this matter? Well, consider what happens when we write</p>
<blockquote><pre>
<blockquote>
<pre>
struct Foo { void bar(int) const; };
const Foo *cp = new Foo;
std::bind1st(std::mem_fun(&Foo::bar), cp);
</pre></blockquote>
std::bind1st(std::mem_fun(&amp;Foo::bar), cp);
</pre>
</blockquote>
<p>We have created a <tt><nobr>const_mem_fun1_t</nobr></tt> object
which will effectively contain the following
<p>We have created a <tt>const_mem_fun1_t</tt> object which will
effectively contain the following</p>
<blockquote><pre>
<blockquote>
<pre>
typedef Foo* first_argument_type;
</pre></blockquote>
</pre>
</blockquote>
<p>The <tt><nobr>bind1st</nobr></tt> will then create a
<tt><nobr>binder1st</nobr></tt> object that will use this
<tt><nobr>typedef</nobr></tt> as the type of a member which will be
initialised with <tt><nobr>cp</nobr></tt>. In other words, we will
need to initialise a <tt><nobr>Foo*</nobr></tt> member with a
<tt><nobr>const Foo*</nobr></tt> pointer! Clearly this is not
possible, so to implement this your Standard Library vendor will have
had to cast away the constness of <tt><nobr>cp</nobr></tt>, probably
within the body of <tt><nobr>bind1st</nobr></tt>.
<p>The <tt>bind1st</tt> will then create a <tt>binder1st</tt> object that
will use this <tt>typedef</tt> as the type of a member which will be
initialised with <tt>cp</tt>. In other words, we will need to initialise a
<tt>Foo*</tt> member with a <tt>const&nbsp;Foo*</tt> pointer! Clearly this
is not possible, so to implement this your Standard Library vendor will
have had to cast away the constness of <tt>cp</tt>, probably within the
body of <tt>bind1st</tt>.</p>
<p>This hack will not suffice with the improved <a
href="binders.html">binders</a> in this library, so we have had to
provide corrected versions of the member function adapters as well.
<p>This hack will not suffice with the improved <a href=
"binders.html">binders</a> in this library, so we have had to provide
corrected versions of the member function adapters as well.</p>
<h3 id="args">Argument Types</h3>
<h3 id="args">Argument Types</h3>
<p>The standard defines <tt>mem_fun1_t</tt>, for example, like this
(&sect;20.3.8&nbsp;&para;2):</p>
<p>The standard defines <nobr><tt>mem_fun1_t</tt></nobr>, for example, like this
<nobr>(&sect;20.3.8 &para;2):</nobr>
<blockquote><pre>
<blockquote>
<pre>
template &lt;class S, class T, class A&gt; class mem_fun1_t
: public binary_function&lt;T*, A, S&gt; {
public:
explicit mem_fun1_t(S (T::*p)(<strong>A</strong>));
S operator()(T* p, <strong>A</strong> x) const;
};
</pre></blockquote>
</pre>
</blockquote>
<p>Note that the second argument to <nobr><tt>operator()</tt></nobr> is
exactly the same type as the argument to the member function. If this
is a value type, the argument will be passed by value and copied twice.
<p>Note that the second argument to <tt>operator()</tt> is exactly the same
type as the argument to the member function. If this is a value type, the
argument will be passed by value and copied twice.</p>
<p>However, if we were to try and eliminate this inefficiency by
instead declaring the argument as <nobr><tt>const A&</tt></nobr>, then
if A were a reference type, we would have a reference to a reference,
which is currently illegal (but see <a
href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
core language issue number 106)</a>
<p>However, if we were to try and eliminate this inefficiency by instead
declaring the argument as <tt>const&nbsp;A&amp;</tt>, then if A were a
reference type, we would have a reference to a reference, which is
currently illegal (but see <a href=
"http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++ core
language issue number 106)</a></p>
<p>So the way in which we want to declare the second argument for
<nobr><tt>operator()</tt></nobr> depends on whether or not the member
function's argument is a reference. If it is a reference, we want to
declare it simply as <nobr><tt>A</tt></nobr>; if it is a value we want
to declare it as <nobr><tt>const A&</tt></nobr>.
<p>So the way in which we want to declare the second argument for
<tt>operator()</tt> depends on whether or not the member function's
argument is a reference. If it is a reference, we want to declare it simply
as <tt>A</tt>; if it is a value we want to declare it as
<tt>const&nbsp;A&amp;</tt>.</p>
<p>The Boost <nobr><a
href="../utility/call_traits.htm">call_traits</a></nobr> class
template contains a <tt><nobr>param_type</nobr></tt> typedef, which
uses partial specialisation to make precisely this decision. By
declaring the <nobr><tt>operator()</tt></nobr> as
<p>The Boost <a href="../utility/call_traits.htm">call_traits</a> class
template contains a <tt>param_type</tt> typedef, which uses partial
specialisation to make precisely this decision. By declaring the
<tt>operator()</tt> as</p>
<blockquote><pre>
<blockquote>
<pre>
S operator()(T* p, typename call_traits&lt;A&gt;::param_type x) const
</pre></blockquote>
</pre>
</blockquote>
<p>we achieve the desired result - we improve efficiency without
generating references to references.</p>
<p>we achieve the desired result - we improve efficiency without generating
references to references.</p>
<h3>Limitations</h3>
<h3>Limitations</h3>
<p>The call traits template used to realise some improvements relies
on partial specialisation, so these improvements are only available on
compilers that support that feature. With other compilers, the
argument passed to the member function (in the
<nobr><tt>mem_fun1_t</tt></nobr> family) will always be passed by
reference, thus generating the possibility of references to references.
<p>The call traits template used to realise some improvements relies on
partial specialisation, so these improvements are only available on
compilers that support that feature. With other compilers, the argument
passed to the member function (in the <tt>mem_fun1_t</tt> family) will
always be passed by reference, thus generating the possibility of
references to references.</p>
<hr>
<hr>
<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
"http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional"
height="31" width="88"></a></p>
<p>Copyright &copy; 2000 Cadenza New Zealand Ltd. Permission to copy,
use, modify, sell and distribute this document is granted provided
this copyright notice appears in all copies. This document is provided
"as is" without express or implied warranty, and with no claim as to
its suitability for any purpose.</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>Revised 28 June 2000</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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<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>
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<td><a href="../../index.htm"><font face="Arial" color=
"#FFFFFF"><big>Home</big></font></a></td>
<h1>Negators</h1>
<td><a href="../libraries.htm"><font face="Arial" color=
"#FFFFFF"><big>Libraries</big></font></a></td>
<p>The header <nobr><a
href="../../boost/functional.hpp">functional.hpp</a></nobr> provides
enhanced versions of both the negator adapters from the C++ Standard
Library (&sect;20.3.5):</p>
<td><a href="../../people/people.htm"><font face="Arial" color=
"#FFFFFF"><big>People</big></font></a></td>
<ul>
<li><tt>unary_negate</tt></li>
<li><tt>binary_negate</tt></li>
</ul>
<td><a href="../../more/faq.htm"><font face="Arial" color=
"#FFFFFF"><big>FAQ</big></font></a></td>
<p>As well as the corresponding helper functions</p>
<td><a href="../../more/index.htm"><font face="Arial" color=
"#FFFFFF"><big>More</big></font></a></td>
</tr>
</table>
<ul>
<li><tt>not1</tt></li>
<li><tt>not2</tt></li>
</ul>
<h1>Negators</h1>
<p>However, the negators in this library improve on the standard
versions in two ways:
<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
provides enhanced versions of both the negator adapters from the C++
Standard Library (&sect;20.3.5):</p>
<ul>
<li>They use <a href="function_traits.html">function object traits</a>
to avoid the need for <tt><nobr>ptr_fun</nobr></tt> when negating a
function rather than an adaptable function object.
</li>
<li>They use Boost <nobr><a
href="../utility/call_traits.htm">call traits</a></nobr> to determine
the best way to declare their arguments and pass them through
to the adapted function (see <a href="#arguments">below</a>).
</li>
</ul>
<ul>
<li><tt>unary_negate</tt></li>
<h3>Usage</h3>
<li><tt>binary_negate</tt></li>
</ul>
<p>Usage is identical to the standard negators. For example,</p>
<p>As well as the corresponding helper functions</p>
<blockquote><pre>
bool bad(const Foo &foo) { ... }
<ul>
<li><tt>not1</tt></li>
<li><tt>not2</tt></li>
</ul>
<p>However, the negators in this library improve on the standard versions
in two ways:</p>
<ul>
<li>They use <a href="function_traits.html">function object traits</a> to
avoid the need for <tt>ptr_fun</tt> when negating a function rather than
an adaptable function object.</li>
<li>They use Boost <a href=
"../utility/call_traits.htm">call&nbsp;traits</a> to determine the best
way to declare their arguments and pass them through to the adapted
function (see <a href="#arguments">below</a>).</li>
</ul>
<h3>Usage</h3>
<p>Usage is identical to the standard negators. For example,</p>
<blockquote>
<pre>
bool bad(const Foo &amp;foo) { ... }
...
std::vector&lt;Foo&gt; c;
...
std::find_if(c.begin(), c.end(), boost::not1(bad));
</pre></blockquote>
</pre>
</blockquote>
<h3 id="arguments">Argument Types</h3>
<h3 id="arguments">Argument Types</h3>
<p>The C++ Standard <nobr>(&sect;20.3.5)</nobr> defines unary negate
like this (binary negate is similar):</p>
<p>The C++ Standard (&sect;20.3.5) defines unary negate like this (binary
negate is similar):</p>
<blockquote><pre>
<blockquote>
<pre>
template &lt;class Predicate&gt;
class unary_negate
: public unary_function&lt;typename Predicate::argument_type,bool&gt; {
public:
explicit unary_negate(const Predicate& pred);
bool operator()(<strong>const typename Predicate::argument_type&</strong> x) const;
};</pre></blockquote>
explicit unary_negate(const Predicate&amp; pred);
bool operator()(<strong>const typename Predicate::argument_type&amp;</strong> x) const;
};
</pre>
</blockquote>
<p>Note that if the Predicate's <nobr><tt>argument_type</tt></nobr> is
a reference, the type of <nobr><tt>operator()</tt>'s</nobr> argument
would be a reference to a reference. Currently this is illegal in C++
(but see the <a
href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">
C++ standard core language active issues list</a>).</p>
<p>Note that if the Predicate's <tt>argument_type</tt> is a reference, the
type of <tt>operator()</tt>'s argument would be a reference to a reference.
Currently this is illegal in C++ (but see the <a href=
"http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
standard core language active issues list</a>).</p>
<p>However, if we instead defined <nobr><tt>operator()</tt></nobr>
to accept Predicate's argument_type unmodified, this would be
needlessly inefficient if it were a value type; the argument would be
copied twice - once when calling <nobr><tt>unary_negate</tt>'s</nobr>
<nobr><tt>operator()</tt></nobr>, and again when <nobr><tt>operator()</tt></nobr>
called the adapted function.</p>
<p>However, if we instead defined <tt>operator()</tt> to accept Predicate's
argument_type unmodified, this would be needlessly inefficient if it were a
value type; the argument would be copied twice - once when calling
<tt>unary_negate</tt>'s <tt>operator()</tt>, and again when
<tt>operator()</tt> called the adapted function.</p>
<p>So how we want to declare the argument for
<nobr><tt>operator()</tt></nobr> depends on whether or not the
Predicate's <nobr><tt>argument_type</tt></nobr> is a reference. If it
is a reference, we want to declare it simply as
<nobr><tt>argument_type</tt></nobr>; if it is a value we want to
declare it as <nobr><tt>const argument_type&</tt></nobr>.
<p>So how we want to declare the argument for <tt>operator()</tt> depends
on whether or not the Predicate's <tt>argument_type</tt> is a reference. If
it is a reference, we want to declare it simply as <tt>argument_type</tt>;
if it is a value we want to declare it as
<tt>const&nbsp;argument_type&amp;</tt>.</p>
<p>The Boost <nobr><a
href="../utility/call_traits.htm">call_traits</a></nobr> class
template contains a <tt><nobr>param_type</nobr></tt> typedef, which
uses partial specialisation to make precisely this decision. If we were
to declare <nobr><tt>operator()</tt></nobr> as</p>
<p>The Boost <a href="../utility/call_traits.htm">call_traits</a> class
template contains a <tt>param_type</tt> typedef, which uses partial
specialisation to make precisely this decision. If we were to declare
<tt>operator()</tt> as</p>
<blockquote><pre>
<blockquote>
<pre>
bool operator()(typename call_traits&lt;typename Predicate::argument_type&gt;::param_type x) const
</pre></blockquote>
</pre>
</blockquote>
<p>the desired result would be achieved - we would eliminate
references to references without loss of efficiency. In fact, the
actual declaration is slightly more complicated because of the use of
function object traits, but the effect remains the same.</p>
<p>the desired result would be achieved - we would eliminate references to
references without loss of efficiency. In fact, the actual declaration is
slightly more complicated because of the use of function object traits, but
the effect remains the same.</p>
<h3>Limitations</h3>
<h3>Limitations</h3>
<p>Both the function object traits and call traits used to realise
these improvements rely on partial specialisation, these improvements
are only available on compilers that support that feature. With other
compilers, the negators in this library behave very much like those
in the Standard - <nobr><tt>ptr_fun</tt></nobr> will be required to
adapt functions, and references to references will not be avoided.
<p>Both the function object traits and call traits used to realise these
improvements rely on partial specialisation, these improvements are only
available on compilers that support that feature. With other compilers, the
negators in this library behave very much like those in the Standard -
<tt>ptr_fun</tt> will be required to adapt functions, and references to
references will not be avoided.</p>
<hr>
<hr>
<p>Copyright &copy; 2000 Cadenza New Zealand Ltd. Permission to copy, use, modify, sell and distribute this document is granted provided this copyright notice appears in all copies. This document is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose.</p>
<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
"http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional"
height="31" width="88"></a></p>
<p>Revised 28 June 2000</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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<h1>Function Pointer Adapters</h1>
<td><a href="../libraries.htm"><font face="Arial" color=
"#FFFFFF"><big>Libraries</big></font></a></td>
<p>The header <nobr><a
href="../../boost/functional.hpp">functional.hpp</a></nobr> provides
enhanced versions of both the function pointer adapters from the C++
Standard Library <nobr>(&sect 20.3.7):</nobr></p>
<td><a href="../../people/people.htm"><font face="Arial" color=
"#FFFFFF"><big>People</big></font></a></td>
<ul>
<li><tt>pointer_to_unary_function</tt></li>
<li><tt>pointer_to_binary_function</tt></li>
</ul>
<td><a href="../../more/faq.htm"><font face="Arial" color=
"#FFFFFF"><big>FAQ</big></font></a></td>
<p>As well as the corresponding helper function template:</p>
<td><a href="../../more/index.htm"><font face="Arial" color=
"#FFFFFF"><big>More</big></font></a></td>
</tr>
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<ul>
<li><tt>ptr_fun</tt></li>
</ul>
<h1>Function Pointer Adapters</h1>
<p>However, you should not need to use the adapters in conjunction
with the adapters in this library due to our use of <a
href="function_traits.html">function object traits</a>. You will
however need to use them if your implementation fails to work properly
with our traits classes (due to lack if partial specialisation), or if
you wish to use a function object adapter from a third party.
<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
provides enhanced versions of both the function pointer adapters from the
C++ Standard Library (&sect;20.3.7):</p>
<h3>Usage</h3>
<ul>
<li><tt>pointer_to_unary_function</tt></li>
<p>If you need to use these adapters, usage is identical to the
standard function pointer adapters. For example,</p>
<li><tt>pointer_to_binary_function</tt></li>
</ul>
<blockquote><pre>
<p>As well as the corresponding helper function template:</p>
<ul>
<li><tt>ptr_fun</tt></li>
</ul>
<p>However, you should not need to use the adapters in conjunction with the
adapters in this library due to our use of <a href=
"function_traits.html">function object traits</a>. You will however need to
use them if your implementation fails to work properly with our traits
classes (due to lack if partial specialisation), or if you wish to use a
function object adapter from a third party.</p>
<h3>Usage</h3>
<p>If you need to use these adapters, usage is identical to the standard
function pointer adapters. For example,</p>
<blockquote>
<pre>
bool bad(std::string foo) { ... }
...
std::vector&lt;std::string&gt; c;
...
std::vector&lt;std::string&gt;::iterator it
= std::find_if(c.begin(), c.end(), std::not1(boost::ptr_fun(bad)));
</pre></blockquote>
</pre>
</blockquote>
<p>Note however that this library contains enhanced <a
href="negators.html">negators</a> that support function object traits,
so the line above could equally be written
<p>Note however that this library contains enhanced <a href=
"negators.html">negators</a> that support function object traits, so the
line above could equally be written</p>
<blockquote><pre>
<blockquote>
<pre>
std::vector&lt;std::string&gt;::iterator it
= std::find_if(c.begin(), c.end(), boost::not1(bad));
</pre></blockquote>
</pre>
</blockquote>
<h3>Argument Types</h3>
<h3>Argument Types</h3>
<p>The standard defines
<nobr><tt>pointer_to_unary_function</tt></nobr> like this
<nobr>(&sect;20.3.8 &para;2):</nobr>
<p>The standard defines <tt>pointer_to_unary_function</tt> like this
(&sect;20.3.8&nbsp;&para;2):</p>
<blockquote><pre>
<blockquote>
<pre>
template &lt;class Arg, class Result&gt;
class pointer_to_unary_function : public unary_function&lt;Arg, Result&gt; {
public:
explicit pointer_to_unary_function(Result (* f)(<strong>Arg</strong>));
Result operator()(<strong>Arg</strong> x) const;
};
</pre></blockquote>
</pre>
</blockquote>
<p>Note that the argument to <nobr><tt>operator()</tt></nobr> is
exactly the same type as the argument to the wrapped function. If this
is a value type, the argument will be passed by value and copied twice.
<nobr><tt>pointer_to_binary_function</tt></nobr> has a similar problem.
<p>Note that the argument to <tt>operator()</tt> is exactly the same type
as the argument to the wrapped function. If this is a value type, the
argument will be passed by value and copied twice.
<tt>pointer_to_binary_function</tt> has a similar problem.</p>
<p>However, if we were to try and eliminate this inefficiency by
instead declaring the argument as <nobr><tt>const Arg&</tt></nobr>, then
if Arg were a reference type, we would have a reference to a reference,
which is currently illegal (but see <a
href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
core language issue number 106)</a>
<p>However, if we were to try and eliminate this inefficiency by instead
declaring the argument as <tt>const&nbsp;Arg&amp;</tt>, then if Arg were a
reference type, we would have a reference to a reference, which is
currently illegal (but see <a href=
"http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++ core
language issue number 106)</a></p>
<p>So the way in which we want to declare the argument for
<nobr><tt>operator()</tt></nobr> depends on whether or not the
wrapped function's argument is a reference. If it
is a reference, we want to declare it simply as
<nobr><tt>Arg</tt></nobr>; if it is a value we want to
declare it as <nobr><tt>const Arg&</tt></nobr>.
<p>So the way in which we want to declare the argument for
<tt>operator()</tt> depends on whether or not the wrapped function's
argument is a reference. If it is a reference, we want to declare it simply
as <tt>Arg</tt>; if it is a value we want to declare it as
<tt>const&nbsp;Arg&amp;</tt>.</p>
<p>The Boost <nobr><a
href="../utility/call_traits.htm">call_traits</a></nobr> class
template contains a <tt><nobr>param_type</nobr></tt> typedef, which
uses partial specialisation to make precisely this decision. By
declaring the <nobr><tt>operator()</tt></nobr> as
<p>The Boost <a href="../utility/call_traits.htm">call_traits</a> class
template contains a <tt>param_type</tt> typedef, which uses partial
specialisation to make precisely this decision. By declaring the
<tt>operator()</tt> as</p>
<blockquote><pre>
<blockquote>
<pre>
Result operator()(typename call_traits&lt;Arg&gt;::param_type x) const
</pre></blockquote>
</pre>
</blockquote>
<p>we achieve the desired result - we improve efficiency without
generating references to references.</p>
<p>we achieve the desired result - we improve efficiency without generating
references to references.</p>
<h3>Limitations</h3>
<h3>Limitations</h3>
<p>The call traits template used to realise this improvement relies
on partial specialisation, so this improvement is only available on
compilers that support that feature. With other compilers, the
argument passed to the function will always be passed by
reference, thus generating the possibility of references to references.
<p>The call traits template used to realise this improvement relies on
partial specialisation, so this improvement is only available on compilers
that support that feature. With other compilers, the argument passed to the
function will always be passed by reference, thus generating the
possibility of references to references.</p>
<hr>
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<p>Copyright &copy; 2000 Cadenza New Zealand Ltd. Permission to copy,
use, modify, sell and distribute this document is granted provided
this copyright notice appears in all copies. This document is provided
"as is" without express or implied warranty, and with no claim as to
its suitability for any purpose.</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>Revised 28 June 2000</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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