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93 lines
3.6 KiB
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93 lines
3.6 KiB
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<title>Header <boost/compressed_pair.hpp></title>
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<h2><img src="../../c++boost.gif" width="276" height="86">Header
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<<a href="../../boost/detail/call_traits.hpp">boost/compressed_pair.hpp</a>></h2>
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<p>All of the contents of <boost/compressed_pair.hpp> are
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defined inside namespace boost.</p>
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<p>The class compressed pair is very similar to std::pair, but if
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either of the template arguments are empty classes, then the
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"empty member optimisation" is applied to compress the
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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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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
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functions first() and second(). Note that not all member
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functions can be instantiated for all template parameter types.
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In particular compressed_pair can be instantiated for reference
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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
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type, then there is only one version of the single-argument
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constructor, and this constructor initialises both values in the
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pair to the passed value.</p>
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<p>Note that compressed_pair can not be instantiated if either of
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the template arguments is an enumerator type, unless there is
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compiler support for boost::is_enum, or if boost::is_enum is
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specialised for the enumerator type.</p>
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<p>Finally, compressed_pair requires compiler support for partial
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specialisation of class templates - without that support
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compressed_pair behaves just like std::pair.</p>
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<hr>
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<p>Revised 08 March 2000</p>
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<p><EFBFBD> Copyright boost.org 2000. Permission to copy, use, modify,
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sell and distribute this document is granted provided this
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copyright notice appears in all copies. This document is provided
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"as is" without express or implied warranty, and with
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no claim as to its suitability for any purpose.</p>
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<p>Based on contributions by Steve Cleary, Beman Dawes, Howard
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Hinnant and John Maddock.</p>
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<p>Maintained by <a href="mailto:John_Maddock@compuserve.com">John
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Maddock</a>, the latest version of this file can be found at <a
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href="http://www.boost.org">www.boost.org</a>, and the boost
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discussion list at <a href="http://www.egroups.com/list/boost">www.egroups.com/list/boost</a>.</p>
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<p> </p>
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</body>
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