Re: Asymmetry of user-difined swap and distance

["Maxim Dementiev" <max at e-soft dot ru>]

On Fri, 7 Aug 2009 19:19:03 +0100
 Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> 2009/8/7 Maxim Dementiev:
> > It means that swap for user types could be defined either in std namespace
> > or in the user type namespace (argument-dependent name lookup).
>
> Yes, this is intentional. swap() is a point of customisation point,
> see http://www.ddj.com/cpp/184401876 and the definition in
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1691.html

Ok. Thanks!

> > On the other hand, distance (advance, etc.) for user types must be defined
> > in std namespace.
>
> There is no need to customise std::distance(), or certainly a lot less
> need, because the Standard Library can provide optimal implementations
> for all possible iterator categories.  The generic swap() function in

Dear Jonathan, what about structures like B-Trees where the speed is equal to random iterators on one node but is lesser when you 
iterates though different nodes?
So, for me the question isn't "Do I really need it?"
But "Shall I extend the std namespace?"

Yours faithfully,
Max