Re: [boost] Re: Fw: An omnipotant swap?

From: Thomas Witt (witt_at_[hidden])
Date: 2003-09-09 09:44:06

Daniel,

Daniel Frey wrote:

> OTOH you need to 
> provide a swap function, so you have to take into account that the class 
> needs to support it anyway by some code.

?

> 
> Some classes might not do that with a member function swap, but with a 
> friend function that has two arguments. Also, most classes that have a 
> member-function also provide a free function with two parameters 
> resolving to the member functions. That given, this might also be a 
> reasonable implementation which might work on more compilers today:

Daniel John is talking about std::swap. Your solution does not adress 
one of the fundamental problems I see. Having a member, what might be 
the natural thing to do, would require a free function as well. This is 
tedious and should be avoided.

> 
> namespace boost
> {
>    template< typename T >
>    inline void swap( T& lhs, T& rhs )
>    {
>       using std::swap;
>       swap( lhs, rhs );
>    }
> }

This is a user solution to libraries(users)-cannot-overload-std::swap. 
AFAICS this is not a solution to the std lib problem.

> 
> ADL should find the better match if T provides a swap(T&,T&), otherwise 
> the default from std:: will be used. The question is IMHO which 
> requirements to T (in a namespace N) we request:
> 
>   void N::T::swap( T& );
> 
> or
> 
>   void N::swap( T&, T& );

This is _a_ question but not _the_ question.

Regards

Thomas

-- 
Dipl.-Ing. Thomas Witt
Institut fuer Verkehrswesen, Eisenbahnbau und -betrieb, Universitaet 
Hannover
voice: [phone] - 4273, fax: [phone]
http://www.ive.uni-hannover.de