...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Copyright © 2000 Steve Cleary, Beman Dawes, Howard Hinnant & John Maddock
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)
Table of Contents
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.
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.
Based on contributions by Steve Cleary, Beman Dawes, Howard Hinnant and John Maddock.
Maintained by John Maddock.
Last revised: December 22, 2016 at 12:36:16 GMT |