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<title>Header </title>
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<boostcompressed_pair.hpp>
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</head>
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<body bgcolor="#ffffff" text="#000000" link="#0000ff" vlink="#800080">
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<h2><img src="../../boost.png" width="276" height="86">Header <<a href="../../boost/detail/compressed_pair.hpp">boost/compressed_pair.hpp</a>></h2>
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<p>All of the contents of <boost/compressed_pair.hpp> are defined inside
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namespace boost.</p>
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<p>The class compressed pair is very similar to std::pair, but if either of the
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template arguments are empty classes, then the "empty base-class optimisation"
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is applied to compress the size of the pair.</p>
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<pre>template <class T1, class T2>
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class compressed_pair
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{
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public:
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typedef T1 first_type;
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typedef T2 second_type;
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typedef typename call_traits<first_type>::param_type first_param_type;
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typedef typename call_traits<second_type>::param_type second_param_type;
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typedef typename call_traits<first_type>::reference first_reference;
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typedef typename call_traits<second_type>::reference second_reference;
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typedef typename call_traits<first_type>::const_reference first_const_reference;
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typedef typename call_traits<second_type>::const_reference second_const_reference;
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compressed_pair() : base() {}
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compressed_pair(first_param_type x, second_param_type y);
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explicit compressed_pair(first_param_type x);
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explicit compressed_pair(second_param_type y);
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2001-05-08 11:17:44 +00:00
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compressed_pair& operator=(const compressed_pair&);
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first_reference first();
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first_const_reference first() const;
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second_reference second();
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second_const_reference second() const;
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void swap(compressed_pair& y);
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};</pre>
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<p>The two members of the pair can be accessed using the member functions first()
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and second(). Note that not all member functions can be instantiated for all
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template parameter types. In particular compressed_pair can be instantiated for
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reference and array types, however in these cases the range of constructors
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that can be used are limited. If types T1 and T2 are the same type, then there
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is only one version of the single-argument constructor, and this constructor
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initialises both values in the pair to the passed value.</p>
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<P>Note that if either member is a POD type, then that member is not
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zero-initialized by the compressed_pair default constructor: it's up to you to
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supply an initial value for these types if you want them to have a default
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value.</P>
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<p>Note that compressed_pair can not be instantiated if either of the template
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arguments is a union type, unless there is compiler support for
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boost::is_union, or if boost::is_union is specialised for the union type.</p>
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<p>Finally, a word of caution for Visual C++ 6 users: if either argument is an
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empty type, then assigning to that member will produce memory corruption,
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unless the empty type has a "do nothing" assignment operator defined. This is
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due to a bug in the way VC6 generates implicit assignment operators.</p>
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<h3>Acknowledgements</h3>
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<p>Based on contributions by Steve Cleary, Beman Dawes, Howard Hinnant and John
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Maddock.</p>
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<p>Maintained by <a href="mailto:john@johnmaddock.co.uk">John Maddock</a>, the
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latest version of this file can be found at <a href="http://www.boost.org">www.boost.org</a>,
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and the boost discussion list at <a href="http://www.yahoogroups.com/list/boost">www.yahoogroups.com/list/boost</a>.</p>
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<hr>
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<p>Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B %Y" startspan -->07 November 2007<!--webbot bot="Timestamp" endspan i-checksum="40338" --></p>
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<p><EFBFBD> Copyright Beman Dawes, 2000.</p>
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<p>Distributed under the Boost Software License, Version 1.0. See
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<a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a></p>
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2005-05-28 11:51:04 +00:00
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</body>
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2007-11-07 16:08:09 +00:00
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</html>
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