forked from boostorg/fusion
Eric Niebler
798b2f4017
https://svn.boost.org/svn/boost/trunk ........ r41077 | troyer | 2007-11-13 23:00:02 -0800 (Tue, 13 Nov 2007) | 1 line Added support for std::complex to serialization ........ r41078 | joaquin | 2007-11-13 23:09:29 -0800 (Tue, 13 Nov 2007) | 1 line added missing include ........ r41079 | djowel | 2007-11-14 02:13:51 -0800 (Wed, 14 Nov 2007) | 1 line adjust to compensate for lack of <small> tag. ........ r41080 | djowel | 2007-11-14 02:17:09 -0800 (Wed, 14 Nov 2007) | 1 line refresh docs ........ r41081 | djowel | 2007-11-14 02:23:23 -0800 (Wed, 14 Nov 2007) | 1 line refresh docs ........ r41082 | djowel | 2007-11-14 02:24:21 -0800 (Wed, 14 Nov 2007) | 1 line refresh docs ........ r41083 | anthonyw | 2007-11-14 03:08:09 -0800 (Wed, 14 Nov 2007) | 1 line ignore and join all threads in group on exception ........ r41084 | anthonyw | 2007-11-14 03:56:53 -0800 (Wed, 14 Nov 2007) | 1 line interrupt and join all threads in a group if an exception is thrown during a test ........ r41086 | johnmaddock | 2007-11-14 04:14:19 -0800 (Wed, 14 Nov 2007) | 1 line Merged changes from the Sandbox to Trunk. ........ r41087 | anthonyw | 2007-11-14 04:17:41 -0800 (Wed, 14 Nov 2007) | 1 line interrupt and join all threads in a group if an exception is thrown during a test ........ r41088 | johnmaddock | 2007-11-14 04:41:32 -0800 (Wed, 14 Nov 2007) | 1 line Added WinCE workaround. ........ r41089 | johnmaddock | 2007-11-14 05:03:15 -0800 (Wed, 14 Nov 2007) | 1 line Catch exceptions thrown from thread creation. ........ r41090 | anthonyw | 2007-11-14 06:49:58 -0800 (Wed, 14 Nov 2007) | 1 line fixes for pthread implementation ........ r41091 | bemandawes | 2007-11-14 07:50:43 -0800 (Wed, 14 Nov 2007) | 1 line Replace old docs with excerpts from http://article.gmane.org/gmane.comp.lib.boost.testing/5020 ........ r41093 | eric_niebler | 2007-11-14 08:36:15 -0800 (Wed, 14 Nov 2007) | 1 line fix support for segmented iteration ........ r41094 | dave | 2007-11-14 09:37:55 -0800 (Wed, 14 Nov 2007) | 3 lines Update command-prompt instructions per http://news.gmane.org/find-root.php?message_id=%3cfhcrem%24c4%241%40ger.gmane.org%3e ........ r41095 | bemandawes | 2007-11-14 12:05:30 -0800 (Wed, 14 Nov 2007) | 1 line Bring docs more in line with reality:-) ........ r41097 | hljin | 2007-11-14 18:07:53 -0800 (Wed, 14 Nov 2007) | 1 line GIL: removed the example directory from the documentation as it is a duplication and re-directed the Doxygen documentation to a local copy (to be submitted next) ........ r41098 | hljin | 2007-11-14 18:30:13 -0800 (Wed, 14 Nov 2007) | 1 line GIL: added a local copy of the Doxygen documentation ........ r41099 | hljin | 2007-11-14 18:32:04 -0800 (Wed, 14 Nov 2007) | 1 line GIL: added a local copy of the Doxygen documentation (second batch) ........ r41100 | chris_kohlhoff | 2007-11-14 22:19:04 -0800 (Wed, 14 Nov 2007) | 6 lines Try to fix an order-of-initialisation problem with error_category references. The symptom, which only occurs in some applications, is a crash due to a dereference of a null pointer. The exact conditions under which the problem occurs are not fully understood, so this fix is probably more paranoid than necessary. ........ r41102 | jhunold | 2007-11-14 23:04:24 -0800 (Wed, 14 Nov 2007) | 1 line Suppress msvc "deprecated" warnings. ........ r41103 | johnmaddock | 2007-11-15 01:52:26 -0800 (Thu, 15 Nov 2007) | 1 line Fix some compiler warnings when building with the Intel and aCC compilers. ........ r41104 | garcia | 2007-11-15 04:50:48 -0800 (Thu, 15 Nov 2007) | 2 lines John Torjo is reviewing the X-files. ........ r41105 | hkaiser | 2007-11-15 05:27:24 -0800 (Thu, 15 Nov 2007) | 1 line Suppressed more warnings during build of Wave. ........ r41106 | bemandawes | 2007-11-15 06:36:40 -0800 (Thu, 15 Nov 2007) | 1 line GetUserDefaultUILanguage isn't present for Cygwin, so disable use ........ r41107 | bemandawes | 2007-11-15 07:20:27 -0800 (Thu, 15 Nov 2007) | 1 line Get rid of .cvsignore files ........ r41108 | eric_niebler | 2007-11-15 08:06:22 -0800 (Thu, 15 Nov 2007) | 1 line fix typo ........ r41110 | grafik | 2007-11-15 08:58:21 -0800 (Thu, 15 Nov 2007) | 1 line Fix building of multiple regression tools at once. ........ r41111 | gmelquio | 2007-11-15 09:52:31 -0800 (Thu, 15 Nov 2007) | 1 line Fixed documentation typo. ........ r41113 | grafik | 2007-11-15 10:56:43 -0800 (Thu, 15 Nov 2007) | 1 line Switch intel-win32 to use static multi thread runtime since the single thread static runtime is no longer available. (fixes #1287) ........ r41114 | andreas_huber69 | 2007-11-15 11:22:12 -0800 (Thu, 15 Nov 2007) | 1 line Added new FAQ item suggested by Chris Paulse. ........ r41116 | guwi17 | 2007-11-15 12:52:37 -0800 (Thu, 15 Nov 2007) | 4 lines This patch now lets the Sun compiler work for most of uBLAS. 'test4' is now failing. Too avoid other compilers complaining about missing return values in some functions where exceptions are thrown, code was added so an arbitatry were chosen. ........ r41117 | danmarsden | 2007-11-15 13:15:47 -0800 (Thu, 15 Nov 2007) | 1 line removing failing test on EDG compilers ........ r41118 | grafik | 2007-11-15 14:05:15 -0800 (Thu, 15 Nov 2007) | 1 line Remove redundant reference to system library. It causes double linking when used indirectly through filesystem. Which can lead to double linking incompatible variants when a specific filesystem variant is requested. ........ r41119 | grafik | 2007-11-15 14:05:22 -0800 (Thu, 15 Nov 2007) | 1 line Oops, forgot we need to use the root boost project settings when building. ........ [SVN r41141]
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<link rel="start" href="../index.html" title="Chapter 1. Fusion 2.0">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="fusion.introduction"></a><a href="introduction.html" title="Introduction">Introduction</a></h2></div></div></div>
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<p>
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An advantage other languages such as Python and Lisp/ Scheme, ML and Haskell,
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etc., over C++ is the ability to have heterogeneous containers that can hold
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arbitrary element types. All the containers in the standard library can only
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hold a specific type. A <tt class="computeroutput"><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></tt>
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can only hold <tt class="computeroutput"><span class="keyword">int</span></tt>s. A <tt class="computeroutput"><span class="identifier">list</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span></tt> can
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only hold elements of type <tt class="computeroutput"><span class="identifier">X</span></tt>,
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and so on.
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</p>
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<p>
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True, you can use inheritance to make the containers hold different types,
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related through subclassing. However, you have to hold the objects through
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a pointer or smart reference of some sort. Doing this, you'll have to rely
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on virtual functions to provide polymorphic behavior since the actual type
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is erased as soon as you store a pointer to a derived class to a pointer to
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its base. The held objects must be related: you cannot hold objects of unrelated
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types such as <tt class="computeroutput"><span class="keyword">char</span></tt>, <tt class="computeroutput"><span class="keyword">int</span></tt>, <tt class="computeroutput"><span class="keyword">class</span>
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<span class="identifier">X</span></tt>, <tt class="computeroutput"><span class="keyword">float</span></tt>,
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etc. Oh sure you can use something like <a href="http://boost.org/doc/html/any.html" target="_top">Boost.Any</a>
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to hold arbitrary types, but then you pay more in terms of runtime costs and
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due to the fact that you practically erased all type information, you'll have
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to perform dangerous casts to get back the original type.
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</p>
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<p>
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The <a href="http://www.boost.org/libs/tuple/doc/tuple_users_guide.html" target="_top">Boost.Tuple</a>
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library written by <a href="http://www.boost.org/people/jaakko_jarvi.htm" target="_top">Jaakko
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Jarvi</a> provides heterogeneous containers in C++. The <tt class="computeroutput"><span class="identifier">tuple</span></tt>
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is a basic data structure that can hold heterogeneous types. It's a good first
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step, but it's not complete. What's missing are the algorithms. It's nice that
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we can store and retrieve data to and from tuples, pass them around as arguments
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and return types. As it is, the <a href="http://www.boost.org/libs/tuple/doc/tuple_users_guide.html" target="_top">Boost.Tuple</a>
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facility is already very useful. Yet, as soon as you use it more often, usage
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patterns emerge. Eventually, you collect these patterns into algorithm libraries.
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</p>
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<p>
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Hmmm, kinda reminds us of STL right? Right! Can you imagine how it would be
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like if you used STL without the algorithms? Everyone will have to reinvent
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their own <span class="emphasis"><em>algorithm</em></span> wheels.
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</p>
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<p>
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Fusion is a library and a framework similar to both <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>
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and the boost <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>.
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The structure is modeled after <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>,
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which is modeled after <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>.
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It is named "fusion" because the library is reminiscent of the "fusion"
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of compile time meta-programming with runtime programming. The library inherently
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has some interesting flavors and characteristics of both <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>
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and <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>.
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It lives in the twilight zone between compile time meta-programming and run
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time programming. <a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>
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containers work on values. MPL containers work on types. Fusion containers
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work on both types and values.
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</p>
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<p>
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Unlike <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>, Fusion
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algorithms are lazy and non sequence-type preserving. What does that mean?
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It means that when you operate on a sequence through a Fusion algorithm that
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returns a sequence, the sequence returned may not be of the same class as the
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original. This is by design. Runtime efficiency is given a high priority. Like
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<a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>, and unlike
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<a href="http://en.wikipedia.org/wiki/Standard_Template_Library" target="_top">STL</a>,
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fusion algorithms are functional in nature such that algorithms are non mutating
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(no side effects). However, due to the high cost of returning full sequences
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such as vectors and lists, <span class="emphasis"><em>Views</em></span> are returned from Fusion
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algorithms instead. For example, the <a href="algorithm/transformation/functions/transform.html" title="transform"><tt class="computeroutput"><span class="identifier">transform</span></tt></a> algorithm does not actually
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return a transformed version of the original sequence. <a href="algorithm/transformation/functions/transform.html" title="transform"><tt class="computeroutput"><span class="identifier">transform</span></tt></a> returns a <a href="view/transform_view.html" title="transform_view"><tt class="computeroutput"><span class="identifier">transform_view</span></tt></a>. This view holds a
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reference to the original sequence plus the transform function. Iteration over
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the <a href="view/transform_view.html" title="transform_view"><tt class="computeroutput"><span class="identifier">transform_view</span></tt></a>
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will apply the transform function over the sequence elements on demand. This
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<span class="emphasis"><em>lazy</em></span> evaluation scheme allows us to chain as many algorithms
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as we want without incurring a high runtime penalty.
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</p>
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<p>
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The <span class="emphasis"><em>lazy</em></span> evaluation scheme where algorithms return views
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allows operations such as <a href="algorithm/transformation/functions/push_back.html" title="push_back"><tt class="computeroutput"><span class="identifier">push_back</span></tt></a> to be totally generic. In
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Fusion, <a href="algorithm/transformation/functions/push_back.html" title="push_back"><tt class="computeroutput"><span class="identifier">push_back</span></tt></a> is actually a generic algorithm
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that works on all sequences. Given an input sequence <tt class="computeroutput"><span class="identifier">s</span></tt>
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and a value <tt class="computeroutput"><span class="identifier">x</span></tt>, Fusion's <a href="algorithm/transformation/functions/push_back.html" title="push_back"><tt class="computeroutput"><span class="identifier">push_back</span></tt></a> algorithm simply returns
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a <a href="view/joint_view.html" title="joint_view"><tt class="computeroutput"><span class="identifier">joint_view</span></tt></a>:
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a view that holds a reference to the original sequence <tt class="computeroutput"><span class="identifier">s</span></tt>
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and the value <tt class="computeroutput"><span class="identifier">x</span></tt>. Functions
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that were once sequence specific and need to be implemented N times over N
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different sequences are now implemented only once.
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</p>
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<p>
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Fusion provides full round compatibility with <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>.
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Fusion sequences are fully conforming <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>
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sequences and <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>
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sequences are fully compatible with Fusion. You can work with Fusion sequences
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on <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a> if you
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wish to work solely on types. In <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>,
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Fusion sequences follow <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>'s
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sequence-type preserving semantics (i.e. algorithms preserve the original sequence
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type. e.g. transforming a vector returns a vector). You can also convert from
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an <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a> sequence
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to a Fusion sequence. For example, there are times when it is convenient to
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work solely on <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>
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using pure <a href="http://www.boost.org/libs/mpl/index.html" target="_top">MPL</a>
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sequences, then, convert them to Fusion sequences as a final step before actual
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instantiation of real runtime objects with data. You have the best of both
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worlds.
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
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Schwinger<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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</p>
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