[Boost-bugs] [Boost C++ Libraries] #2243: value_initialized should have its own swap functions

Subject: [Boost-bugs] [Boost C++ Libraries] #2243: value_initialized should have its own swap functions
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2008-08-21 19:32:56

#2243: value_initialized should have its own swap functions
------------------------------+---------------------------------------------
 Reporter:  niels_dekker      |       Owner:  no-maintainer
     Type:  Feature Requests  |      Status:  new          
Milestone:  Boost 1.37.0      |   Component:  utility      
  Version:  Boost 1.36.0      |    Severity:  Problem      
 Keywords:                    |  
------------------------------+---------------------------------------------
 For a given type {{{T}}}, the current (1.36.0) version of
 {{{boost::value_initialized<T>}}} is ''only'' Swappable if it is both
 !CopyConstructible and !CopyAssignable.  IMO, {{{value_initialized<T>}}}
 should be Swappable whenever {{{T}}} is Swappable. Moreover, when swapping
 {{{value_initialized<T>}}} objects, the custom swap function of {{{T}}}
 should be used, whenever available.

 I'd like to propose resolving this issue by adding a swap member function
 to {{{value_initialized<T>}}}, and a non-member swap that calls the
 member. (As recommended by Scott Meyers, Effective C++ Third Edition, Item
 25: ''Consider support for a non-throwing swap.'')

 I would like to have {{{value_initialized<T>::swap}}} calling
 {{{boost::swap}}} to swap its data, using the
 [http://svn.boost.org/svn/boost/trunk/boost/utility/swap.hpp  boost::swap
 utility] by Joseph Gauterin ''et al'', that was recently added to the
 trunk. The boost::swap utility internally uses ''argument-dependent
 lookup'' (ADL) to find the custom swap function of {{{T}}}, if available.
 Thereby it works around various compiler version specific bugs regarding
 ADL, as tested at [http://www.boost.org/development/tests/trunk/developer

 /utility-swap_.html utility-swap_.html]. Moreover, it supports swapping
 arrays (as requested by ticket #2056), so {{{value_initialized<T>::swap}}}
 would also support having {{{T}}} as a built-in array type.

 Please take a look at the attached patch.

-- 
Ticket URL: <http://svn.boost.org/trac/boost/ticket/2243>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.