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- [/
- Copyright 2000 Beman Dawes & John Maddock.
- Distributed under the Boost Software License, Version 1.0.
- See accompanying file LICENSE_1_0.txt
- or copy at http://boost.org/LICENSE_1_0.txt
- ]
- [article Compressed_Pair
- [quickbook 1.5]
- [authors [Cleary, Steve]]
- [authors [Dawes, Beman]]
- [authors [Hinnant, Howard]]
- [authors [Maddock, John]]
- [copyright 2000 Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock]
- [license
- 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])
- ]
- ]
- [section Overview]
- All of the contents of `<boost/compressed_pair.hpp>` are defined inside
- `namespace boost`.
- The class `compressed_pair` is very similar to `std::pair`, but if either of
- the template arguments are empty classes, then the ['empty base-class
- optimisation] is applied to compress the size of the pair.
- [endsect]
- [section Synopsis]
- template <class T1, class T2>
- class compressed_pair
- {
- public:
- typedef T1 first_type;
- typedef T2 second_type;
- typedef typename call_traits<first_type>::param_type first_param_type;
- typedef typename call_traits<second_type>::param_type second_param_type;
- typedef typename call_traits<first_type>::reference first_reference;
- typedef typename call_traits<second_type>::reference second_reference;
- typedef typename call_traits<first_type>::const_reference first_const_reference;
- typedef typename call_traits<second_type>::const_reference second_const_reference;
- compressed_pair() : base() {}
- compressed_pair(first_param_type x, second_param_type y);
- explicit compressed_pair(first_param_type x);
- explicit compressed_pair(second_param_type y);
- compressed_pair& operator=(const compressed_pair&);
- first_reference first();
- first_const_reference first() const;
- second_reference second();
- second_const_reference second() const;
- void swap(compressed_pair& y);
- };
- The two members of the pair can be accessed using the member functions
- `first()` and `second()`. Note that not all member functions can be
- instantiated for all template parameter types. In particular
- `compressed_pair` can be instantiated for reference and array types,
- however in these cases the range of constructors that can be used are
- limited. If types `T1` and `T2` are the same type, then there is only
- one version of the single-argument constructor, and this constructor
- initialises both values in the pair to the passed value.
- Note that if either member is a POD type, then that member is not
- zero-initialized by the `compressed_pair` default constructor: it's up
- to you to supply an initial value for these types if you want them to have
- a default value.
- Note that `compressed_pair` can not be instantiated if either of the
- template arguments is a union type, unless there is compiler support for
- `boost::is_union`, or if `boost::is_union` is specialised for the union
- type.
- Finally, a word of caution for Visual C++ 6 users: if either argument is an
- empty type, then assigning to that member will produce memory corruption,
- unless the empty type has a "do nothing" assignment operator defined. This
- is due to a bug in the way VC6 generates implicit assignment operators.
- [endsect]
- [section Acknowledgments]
- Based on contributions by Steve Cleary, Beman Dawes, Howard Hinnant and
- John Maddock.
- Maintained by [@mailto:john@johnmaddock.co.uk John Maddock].
- [endsect]
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