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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] Return-Path: <mark.rodgers -at- cadenza.co.nz> Authentication-Results: mta550.mail.mud.yahoo.com from=cadenza.co.nz; domainkeys=neutral (no sig) Received: from 195.112.4.54 (EHLO smtp.nildram.co.uk) (195.112.4.54) by mta550.mail.mud.yahoo.com with SMTP; Fri, 01 Dec 2006 12:59:40 -0800 Received: from snagglepuss.cadenza.co.nz (81-6-246-87.dyn.gotadsl.co.uk [81.6.246.87]) by smtp.nildram.co.uk (Postfix) with ESMTP id D32EA2B6D8C for <ahd6974-boostorg -at- yahoo.com>; Fri, 1 Dec 2006 20:59:35 +0000 (GMT) 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> In-Reply-To: <379990.36007.qm@web33507.mail.mud.yahoo.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Length: 812 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" > > 3. (Optional) I would also want to convert all HTML files to conform > the HTML 4.01 Standard by running them through HTML Tidy, see > <http://tidy.sf.net> > > It would be great if you could grant me permission to do 1 & 2 and > optionally also 3. > > Thank you! > > Regards, > > Andreas Huber > [SVN r36245]
202 lines
6.7 KiB
HTML
202 lines
6.7 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<meta http-equiv="Content-Language" content="en-us">
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<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
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<title>Boost Function Object Adapter Library</title>
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</head>
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<body bgcolor="#FFFFFF" text="#000000">
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<table border="1" bgcolor="#007F7F" cellpadding="2" summary="">
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<tr>
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<td bgcolor="#FFFFFF"><img src="../../boost.png" alt=
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"boost.png (6897 bytes)" width="277" height="86"></td>
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<td><a href="../../index.htm"><font face="Arial" color=
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"#FFFFFF"><big>Home</big></font></a></td>
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<td><a href="../libraries.htm"><font face="Arial" color=
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"#FFFFFF"><big>Libraries</big></font></a></td>
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<td><a href="../../people/people.htm"><font face="Arial" color=
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"#FFFFFF"><big>People</big></font></a></td>
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<td><a href="../../more/faq.htm"><font face="Arial" color=
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"#FFFFFF"><big>FAQ</big></font></a></td>
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<td><a href="../../more/index.htm"><font face="Arial" color=
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"#FFFFFF"><big>More</big></font></a></td>
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</tr>
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</table>
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<h1>Member Function Adapters</h1>
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<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
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includes improved versions of the full range of member function adapters
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from the the C++ Standard Library (§20.3.8):</p>
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<ul>
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<li><tt>mem_fun_t</tt></li>
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<li><tt>mem_fun1_t</tt></li>
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<li><tt>const_mem_fun_t</tt></li>
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<li><tt>const_mem_fun1_t</tt></li>
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<li><tt>mem_fun_ref_t</tt></li>
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<li><tt>mem_fun1_ref_t</tt></li>
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<li><tt>const_mem_fun_ref_t</tt></li>
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<li><tt>const_mem_fun1_ref_t</tt></li>
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</ul>
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<p>as well as the corresponding overloaded helper functions</p>
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<ul>
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<li><tt>mem_fun</tt></li>
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<li><tt>mem_fun_ref</tt></li>
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</ul>
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<p>The following changes have been made to the adapters as specified in the
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Standard:</p>
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<ul>
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<li>The <tt>first_argument_type</tt> typedef has been corrected for the
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<tt>const_</tt> family of member function adapters (see <a href=
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"#firstarg">below</a>).</li>
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<li>The argument passed to <tt>mem_fun1_t</tt> and its variants is passed
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using the <tt>call_traits::param_type</tt> for the member function's
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argument type.</li>
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</ul>
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<h3 id="firstarg">first_argument_type</h3>
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<p>The standard specifies <tt>const_mem_fun1_t</tt>, for example, like
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this:</p>
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<blockquote>
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<pre>
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template <class S, class T, class A> class const_mem_fun1_t
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: public binary_function<<strong>T*</strong>, A, S> {
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public:
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explicit const_mem_fun1_t(S (T::*p)(A) const);
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S operator()(<strong>const T*</strong> p, A x) const;
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};
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</pre>
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</blockquote>
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<p>Note that the first argument to <tt>binary_function</tt> is <tt>T*</tt>
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despite the fact that the first argument to <tt>operator()</tt> is actually
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of type <tt><em>const</em> T*</tt>.</p>
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<p>Does this matter? Well, consider what happens when we write</p>
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<blockquote>
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<pre>
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struct Foo { void bar(int) const; };
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const Foo *cp = new Foo;
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std::bind1st(std::mem_fun(&Foo::bar), cp);
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</pre>
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</blockquote>
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<p>We have created a <tt>const_mem_fun1_t</tt> object which will
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effectively contain the following</p>
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<blockquote>
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<pre>
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typedef Foo* first_argument_type;
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</pre>
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</blockquote>
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<p>The <tt>bind1st</tt> will then create a <tt>binder1st</tt> object that
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will use this <tt>typedef</tt> as the type of a member which will be
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initialised with <tt>cp</tt>. In other words, we will need to initialise a
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<tt>Foo*</tt> member with a <tt>const Foo*</tt> pointer! Clearly this
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is not possible, so to implement this your Standard Library vendor will
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have had to cast away the constness of <tt>cp</tt>, probably within the
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body of <tt>bind1st</tt>.</p>
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<p>This hack will not suffice with the improved <a href=
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"binders.html">binders</a> in this library, so we have had to provide
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corrected versions of the member function adapters as well.</p>
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<h3 id="args">Argument Types</h3>
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<p>The standard defines <tt>mem_fun1_t</tt>, for example, like this
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(§20.3.8 ¶2):</p>
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<blockquote>
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<pre>
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template <class S, class T, class A> class mem_fun1_t
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: public binary_function<T*, A, S> {
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public:
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explicit mem_fun1_t(S (T::*p)(<strong>A</strong>));
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S operator()(T* p, <strong>A</strong> x) const;
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};
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</pre>
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</blockquote>
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<p>Note that the second argument to <tt>operator()</tt> is exactly the same
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type as the argument to the member function. If this is a value type, the
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argument will be passed by value and copied twice.</p>
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<p>However, if we were to try and eliminate this inefficiency by instead
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declaring the argument as <tt>const A&</tt>, then if A were a
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reference type, we would have a reference to a reference, which is
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currently illegal (but see <a href=
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"http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_active.html#106">C++ core
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language issue number 106)</a></p>
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<p>So the way in which we want to declare the second argument for
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<tt>operator()</tt> depends on whether or not the member function's
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argument is a reference. If it is a reference, we want to declare it simply
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as <tt>A</tt>; if it is a value we want to declare it as
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<tt>const A&</tt>.</p>
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<p>The Boost <a href="../utility/call_traits.htm">call_traits</a> class
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template contains a <tt>param_type</tt> typedef, which uses partial
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specialisation to make precisely this decision. By declaring the
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<tt>operator()</tt> as</p>
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<blockquote>
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<pre>
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S operator()(T* p, typename call_traits<A>::param_type x) const
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</pre>
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</blockquote>
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<p>we achieve the desired result - we improve efficiency without generating
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references to references.</p>
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<h3>Limitations</h3>
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<p>The call traits template used to realise some improvements relies on
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partial specialisation, so these improvements are only available on
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compilers that support that feature. With other compilers, the argument
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passed to the member function (in the <tt>mem_fun1_t</tt> family) will
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always be passed by reference, thus generating the possibility of
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references to references.</p>
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<hr>
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<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
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"http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional"
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height="31" width="88"></a></p>
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<p>Revised
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<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->02 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38510" --></p>
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<p><i>Copyright © 2000 Cadenza New Zealand Ltd.</i></p>
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<p><i>Distributed under the Boost Software License, Version 1.0. (See
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accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
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copy at <a href=
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"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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</body>
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</html>
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